Top Banner
Transport and Development of Microemulsion- and Surfactant Stabilized Iron Nanoparticles for In Situ Remediation By Dennis Hsu A thesis submitted in conformity with the requirements for the degree of Master of Applied Science Department of Chemical Engineering and Applied Chemistry University of Toronto © Copyright by Dennis Hsu (2017)
111

Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

May 16, 2020

Download

Documents

dariahiddleston
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

TransportandDevelopmentofMicroemulsion-andSurfactantStabilizedIronNanoparticlesfor

InSituRemediation

By

DennisHsu

Athesissubmittedinconformitywiththerequirements

forthedegreeofMasterofAppliedScience

DepartmentofChemicalEngineeringandApplied

ChemistryUniversityofToronto

©CopyrightbyDennisHsu(2017)

Page 2: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

ii

ColumnTransportStudyofSurfactant-andMicroemulsion-StabilizedIronNanoparticlesinPorous

Media

DennisHsu

MastersofAppliedScience

GraduateDepartmentofChemicalEngineeringandAppliedChemistryUniversityofToronto

2017

Abstract

Thisworkdescribesthemobilityassessmentsofmicroemulsion-stabilizedironoxide

nanoparticlesandanionicsurfactantsodiumdiethylhexylphosphate(SDEHP)-stabilized

nanoscalezerovalentiron(NZVI)particlesinlaboratoryporousmedia.Thetwoformulations

testedinthisworkachievedstableironnanoparticlesuspensionsformonthsandpreparedviaa

simple“one-pot”synthesismethoddevelopedbyWangetal.Bothformulationsweretested

underfieldscalevelocityof5m/daywithnomechanicalaidduringtheinjection.Athree-

compartmentmodel,involvingcolloiddiffusiontheory,diffusiontheoryandtailingwasapplied

todescribethebreakthroughcurvesofthestudies.Theobtainedbreakthroughcurvesofboth

formulationsimpliedexcellenttransportinporousmediawithsteadyplateauC/Coat0.8-0.9

andrecoveryofupto0.95forSDEHPstabilizedNZVI.Postanalysisontheretentionofironon

theporousmediaimpliedidealtransportwithconsistentdatatothebreakthroughcurves.

Page 3: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

iii

Acknowledgement

Iwouldliketogivemydeepestandsincerestgratitudetomysupervisor,ProfessorEdgar

Acosta,forhisguidance,mentoringandsupportoverthelasttwoyearsofmystudy.Ihave

neverreceivedmoreinspirationsandencouragementsinlife,careerandacademicallatonce

fromanyoneinmylife.Ihavebecomeabetterthinkerinacademiaandlifewithhisguidance.It

wasanhonourtobehisstudent.

IalsowanttothankProfessorSleep,Dr.MondalandDr.LimafromtheRENEWprogram.Iam

verygratefultobeinthisprogramforbetterresearchandcareerdevelopment.Iwanttothank

ProfessorSleeptoprovidemetheaccesstotheuseofglovebox.Itwasavitalpartofthisstudy.

IwanttothankDr.MondalforgivingmesuggestionsinmyresearchandDr.Limaformaking

myMaster’sexperiencemorerewarding.

Iwanttothankallmycolleaguesandfriends,FrancisChoi,AmericoBoza,SilviaZarate,Aurelio

Stammitti,MehdiNouraei,AshuBhanotandSasanMehrabianforhelpingmewithmyresearch.

IparticularlywanttothankSilviaforhelpingmetostartmyresearch,Americoforprovidinghis

knowledgeincolloidalscienceandFrancisforcollaboratinghisworkwithme.

Iwouldalsoliketothankmyparentsandmybrotherfortheirunconditionalsupport.

Finally,IwanttothankmysoulmateJessicaKokforbeingthereformewheneverIneedher

duringmystudy.

Page 4: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

iv

TABLEOFCONTENT

CHAPTER1:INTRODUCTION.................................................................................................................11.2REFERENCE:...........................................................................................................................................8

CHAPTER2:TRANSPORTOFMICROEMULSION-STABILIZEDIRONOXIDEINPOROUSMEDIA..............11ABSTRACT.................................................................................................................................................112.1INTRODUCTION....................................................................................................................................122.2METHODOLOGY...................................................................................................................................16

2.2.1SynthesisofMicroemulsionIronOxide.....................................................................................162.2.2Determiningthestabilityofmicroemulsionironoxide.............................................................172.2.3Viscositystudyofmicroemulsionironoxideformulations........................................................172.2.4Sizecharacterizationofmicroemulsionironoxideandmicroemulsionformulations..............172.2.5Columnstudy............................................................................................................................182.2.6.BreakthroughCurveModeling.................................................................................................222.3.1StabilityTest.............................................................................................................................262.3.2RheologicalProperties..............................................................................................................272.3.3SizeCharacterization................................................................................................................302.3.4μEIronOxideTransport............................................................................................................312.3.5IronDistributionAnalysis..........................................................................................................40

2.4CONCLUSIONS.....................................................................................................................................42

CHAPTER3:DEVELOPMENTANDTRANSPORTOFPHOSPHATESURFACTANT,SDEHP-STABILIZEDNZVIINPOROUSMEDIAFORINSITUREMEDIATION..................................................................................47

3.0ABSTRACT...........................................................................................................................................473.1INTRODUCTION....................................................................................................................................483.2METHODOLOGY...................................................................................................................................53

3.2.1SynthesisofSodiumDiEthylHexylPhosphate(SDEHP)Surfactant...........................................533.2.2CriticalMicelleConcentrationofSDEHPwithdissolvediron....................................................543.2.3TotalOrganicCarbon(TOC)ofirondissolvedSDEHP...............................................................543.2.4SynthesisofSDEHPNZVI...........................................................................................................543.2.5pHAnalysis...............................................................................................................................563.2.6StabilityAnalysis.......................................................................................................................563.2.7ViscosityAnalysis......................................................................................................................573.2.8ColumnExperimentProcedure.................................................................................................573.2.9NZVIColumnDistributionAnalysis...........................................................................................59

3.3RESULTSANDDISCUSSION.....................................................................................................................593.3.1DeterminingtheOptimalSynthesisFormulation......................................................................593.3.2SynthesisResultsandStabilityofFeSO4-basedSDEHPNZVIat100mMand1g/L.................643.3.3pHandViscosityAnalysisandImplication................................................................................683.3.4SizeAnalysisofSDEHPNZVI......................................................................................................693.3.5MobilityofSDEHPNZVIat100mMand1g/L..........................................................................713.3.7ImplicationsforinsituRemediation.........................................................................................75

3.4CONCLUSION.......................................................................................................................................76

CHAPTER4:CONCLUSIONANDRECOMMENDATIONS........................................................................844.2REFERENCES:.......................................................................................................................................89

APPENDIXA–FERRICCHLORIDEBASEDSODIUMDIETHYLHEXYLPHOSPHATE(SDEHP)-STABILIZEDNZVI...................................................................................................................................................90

A.1INTRODUCTION...................................................................................................................................90

Page 5: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

v

A.2METHODOLOGY...................................................................................................................................91A.2.1PreparationofSurfactantSDEHPandFeCl3-basedNZVI.........................................................91A.2.2FormulationdesignofFeCl3-basedNZVI..................................................................................91A.2.3CharacterizationAnalysis:SizeandStability............................................................................92

A.3RESULTSANDDISCUSSIONS...................................................................................................................92A.3.1FormulationDesignImplication...............................................................................................92A.3.2StabilityandSizeAnalysis.........................................................................................................93

A.4FUTUREWORKS..................................................................................................................................95A.5REFERENCES:.......................................................................................................................................97

APPENDIXB:COMPARISONBETWEENCARBOXYLMETHYL-CELLUOSESTABILIZEDIRONOXIDENANOPARTICLESWITHMICROEMULSION-STABILIZEDNANOPARTICLES.............................................98

B1.BACKGROUND:....................................................................................................................................98B2.RESULTS:............................................................................................................................................98B2.1.STABILITY.........................................................................................................................................98B2.2.MOBILITYCOMPARISON.....................................................................................................................99

Page 6: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

vi

ListofFigures

Figure1.1ReactionschematicsummaryofNZVI,adaptedfromFuetal....................................2Figure1.2A.SchematicofwormlikemicelleandB.theinteractionbetweenwormlikemicelles

byWangetal.andnanoparticles..........................................................................................6Figure2.1Columnexperimentconfiguration.............................................................................19Figure2.2Injectionscheduleofthecolumnstudies...................................................................21Figure2.3Schematicofthethree-compartmentmodelusedtorepresentthereversible

adsorptionofparticle,advection/dispersioncolumntransport,andparticleattachment.22Figure2.4TimelapsephotocomparisonsofμEironoxideandbareironoxide:(A)10g/LμE

ironoxide.(B)5g/LμEironoxide.(C)10g/Lbareironoxidenanoparticles......................27Figure2.5Viscosityprofilegraph(logscaled)ofμEironoxide(a)andME(b),comparison

betweentheoriginalformulationsanddilutionwithNaClbrinesolution(10g/100mL)at1:1ratio...................................................................................................................................29

Figure2.6TEMimagingofMicroemulsionironoxideat5g/Lwith100nmasscale(a)andmicroemulsionNZVIat1g/LbyWangetal.........................................................................31

Figure2.7Transportofironoxidesuspensionsin1-cmdiameter(highaspectratio)columnat5m/dayporevelocity(a)10g/Lironoxide(b)5g/Lironoxide.............................................33

Figure2.8Breakthroughcurvesof5g/L(asFe)μEsuspensionofironoxideinjectedat5m/day(porevelocity)throughcolumnswithaspectratioof15(left)and6(right).Thesolidlinesshowthesolutionofthe3-compartmentmodelusingtheconstantssummarized............34

Figure2.9Breakthroughcurvesobtainedfor5g/LμEironoxideinjectedat5m/day(porevelocity)througha2.5cmx15cmcolumn(aspectratioof6),usingscheduleA(10%NaClconditioning/rinsingfluid)andscheduleB(deionizedwaterconditioning/rinsingfluid.....37

Figure2.10BreakthroughcurvesobtainedfordilutedμEs(noironoxide)injectedat5m/day(porevelocity)througha2.5cmx15cmcolumn(aspectratioof6),usingscheduleA(10%NaClconditioning/rinsingfluid)andscheduleB(deionizedwaterconditioning/rinse).......38

Figure2.11Ironoxidedepositedonsandcolumnaftertheinjectionof1.5PVof5g/L(asFe)ironoxidenanoparticlesat5m/day(porevelocity)througha2.5cmx15cmcolumn(aspectratioof6),usingscheduleA(10%NaClconditioning/rinsingfluid)andscheduleB(deionizedwaterconditioning/rinsingfluid).Thesolidlinerepresentsthepredictionofdepositedironfromthe3-compartmentmodel..................................................................41

Figure3.1StructureofanionicphosphatesurfactantSDEHP....................................................51Figure3.2Illustrationofthe“one-pot”synthesisprocedureofSDEHP-stabilizedNZVI.The

procedurewasconductedintheglovebox..........................................................................56Figure3.3ColumnstudysetupforSDEHP-stabilizedNZVI.........................................................59Figure3.4Surfacetensionmeasurementsof1g/LofNZVIdissolved:Curve1showsthe

surfacetensionmeasurementoftheoriginalSDEHPconcentrationandCurve2displayedthecorrectedconcentrationofSDEHP................................................................................62

Figure3.5DissolvedSDEHPequilibriumconcentrationwithironVS.addedironsulfateconcentrationsfordifferentinitialSDEHPconcentrations..................................................63

Page 7: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

vii

Figure3.6TEMimagingof10mMSDEHP-stabilizedNZVIat1g/Lwithdifferentscaleat500nmscale...............................................................................................................................64

Figure3.7SetA,TimelapsephotosofSDEHP-stabilizedNZVIat0.5g/LofNZVIatvariousSDEHPconcentrations:a.30mMofSDEHPb.50mMofSDEHPandc.100mMofSDEHP...............................................................................................................................................65

Figure3.8SetB,Stabilitytimelapsepictureof100mMatNZVIconcentration1,1.5and2g/Loveraperiodof24hours:a.1hourandb.24hoursaftersynthesisandre-suspension....67

Figure3.9ColumnstudybreakthroughcurveofhighlystableSDEHP-stabilizedNZVI,at100mMSDEHPand1g/LofNZVIat5m/daywiththemodeldescribedinchapter2(solidline)...............................................................................................................................................73

FigureA1.FigureA1.SurfacetensionmeasurementsofSDEHPatvariousconcentrationwith

ironchloride(1g/LequivalenceofNZVI)dissolved............................................................93FigureA2.FigureA2.Ferricchloride-basedNZVIat100mMofSDEHP@0.3g/Lofiron

concentration.1houraftersynthesis..................................................................................95FigureB1.A.TimelapsedphotosofCMCandmicroemulsionstabilizedironoxideat2.5g/L.B.

EvidenceofsettlingofCMCironoxideafter80hoursuponsuspension.............................99FigureB2.Comparisonofpressuredropmonitoringresultsatthepost-flushingstagebetween

CMCandmicroemulsionironoxide...................................................................................101FigureB3.Iron-sandgrainanalysiswithmicroscopepicturesforA.Microemulsionironoxideat

2.5g/LandB.CMCironoxideat2.5g/L............................................................................102

Page 8: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

viii

LiterofTables

Table2.1Summaryofbreakthroughcurveparameters.............................................................40

Table3.1LiteraturesummaryofcolumnstudiesandstabilitybehaviourfordifferenttypesofsurfacemodifiedironoxideandZVInanoparticles..............................................................52

Table3.2SynthesisresultandcharacterizationofSDEHP-stabilizedNZVIatvariousNZVIandsurfactantconcentrations....................................................................................................67

Page 9: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

1

Chapter1:Introduction

Nano-scalezerovalentiron(NZVI)arereactivemetalnanoparticlesartificiallyreducedfrom

Fe2+orFe3+thatholdsahighredoxpotential(E0=−0.44V)duetothezero-valentarounditas

showninfigure1[1].Becauseofthehighredoxpotential,NZVIarecapableofreducingawide

rangeofchemicals,includingchlorinatedorganiccompounds,nitricaromaticcompoundsand

heavymetals[1][2][3],asdemonstratedinfigure1.1.NZVIparticlesalsoholdhighsurfaceareas

duetothenano-scalesizerangingfrom1to250nmthatincreasetherateofreduction

reactions[4][5].Becauseoftheabovefeatures,inthelasttwodecades,NZVIhasbeen

identifiedasapotentialefficientinsitugroundwaterremediationtechnologycomparingto

otherexistingtechnologies[6].ItisexpectedthatwiththedirectcontactbetweentheNZVI

particlesandthesourceofthecontaminantcanactivelyandrapidlyreducethecontaminant

zoneconcentrationandachievedfullremediation[7].Inspecific,inanindustrial-scaleinsitu

NZVIremediation,stabilizedNZVIaretobeinjectedthroughmultipleinjectionwellsvia

differentinjectiontechnologysuchaspressure-pulseorgravityinjection[8][9].Theamountof

NZVIinjectedisdeterminedbasedonthecontaminantconcentrationsfromthe

characterizationofthesitepriortoinjection.Uponinjections,theNZVIistobeleftinthesoil

fortreatingthecontaminantsoveraperiodfromweekstomonths;forbetterresults

recirculationofthegroundwaterisoftenscheduledperiodicallytopromotethemobility.

Duringthisperiod,concentrationoftheironandcontaminantsaremonitoredfrommonitoring

wellsforprogressandhydrauliccontrol.Extractionwellsareinstalledatdownstreamtocollect

transportedNZVIparticles.

Page 10: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

2

However,injectingNZVIparticlessuspensionintothesoiltoachieveeffectivegroundwater

remediationisacomplexprocedure;O’Carrolletal.summarizedintothefollowing3steps:(1)

Transportingthereactiveparticlesthroughthesoilmatrix(2)Formingcontacttothe

contaminantzoneand(3)Reactingwiththecontaminantstoachieveremediation[10].NZVI

suspensionholdanundesirablepropertyoffastaggregationandsedimentationduetothehigh

stabilitycontributedbythemagneticattractionforcesbetweentheparticle[11].Thisfeature

failsNZVItoachievethefirststepofconductingtheinsituremediation—thelarger,

aggregatedzero-valentparticleswillexperiencefiltrationinthesoilmatrixandironparticles

willattachtothesoilgrain,keepingtheNZVIparticlesfromreachingthedeepercontaminant

zone[12].Thetransportandmobilityoftheironparticlesintheporousmediaisidentifiedas

themajorobstacleofNZVIinsituremediation.Tothisdate,NZVIinjectionhasremainedasan

state-of-the-arttechnologyandresearchhasbeenactivelydoneonimprovingthetransport.

Figure1.1ReactionschematicsummaryofNZVI,adaptedfromFuetal.[1].

Page 11: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

3

LiteraturereviewsuggestedthatimprovingthestabilityoftheNZVIsuspensioncanimprovethe

mobilityofNZVIintheporousmedia[10],[11].Inspecific,astablenanoparticlesuspension

eliminatestheissueofaggregationandsedimentation:ThismeansthatastableNZVI

nanoparticleparticlecanremaininthenano-scalesize,travelbetweensandgrainswithout

filtrationandmaximumamountofNZVIcanbetransported.Currently,themostdirectand

commontechniqueofimprovingthestabilityofNZVIistoapplysurfacemodificationstothe

surfaceofNZVI.Applyingsurfacemodifiers,therepulsionforcesbetweentheironmetal

nanoparticlescanbereducedduetotheadditionofthebarrierandachievehigherstability.

Surfacemodifiersareproventohavepositiveinfluencesonimprovingthestabilityasearlyas

10yearsago[4],[13];however,theresearchonimprovingthestabilityandmobilityisstill

ongoing.Recentstudieshaveshownthatpolymeradsorptionisthemostcommonwayto

stabilizingNZVI,foodgradepolymersuchascarboxyl-methylcellulose[11],[14]–[16],PV3A[17]

andPAA[17].Ontheotherhand,biodegradablesurfaceactiveagentssuchasTween80[18],

SDBS[19]andbiodegradablesurfactants[20]havealsoshownsomeprogressinthisfield.Itis

worthmentioningthatemulsioninducedNZVIhasdrawnalotofattentionasanalternative

wayofstabilizingZVIparticleswithoutsurfaceadsorption[21],[9],[22].However,outofthe

above,theinstabilitywasstillobservedintheabovestudies,forexample,carboxyl-methyl

cellulosebasedNZVIcanremainstableforabout80hourswhileaggregationandsedimentation

areconstantlyobserved[16].Furthermore,Tween80surfactant-basedNZVIalthoughclaimed

remainingstableformonthsinstoragecondition,onceinfieldcondition,thestabilityis

disturbed[18].EmulsioninducedNZVIontheotherhandholdsakineticallystabilityof8hours

whilerequiringmechanicalforceduringinjection[9].Despitescholarshaveinputgreatefforts

Page 12: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

4

intostabilizingNZVItoimprovemobility,therehasnotbeenaNZVIsurfacemodifierthat

completelyeliminatesaggregationandsedimentation.

Laboratory1-Dcolumnstudyisusuallythefirststepinevaluatingthemobilityofasurface

modifiedNZVIbeforescalinguptoafieldremediation.ThesurfacemodifiedNZVIsuspensions,

includingtheabovedescribed,weretestedinvarioussimilarbenchscalecolumnsettingsthat

generallyimpliedthreeissues:1.Flowvelocity:mostofthelaboratorycolumnstudieswere

conductedatarelativelyhighflowratefrom8to200m/day[23][17][18],thisisunrealistic,

consideringtypicalfieldapplicationsareconductedat0.25-4m/day[8].2Performance:as

mentioned,instabilitywasstillobservedinallthesurfacemodifiedNZVIthusfar,itwas

constantlyreportedthatthehighestbreakthroughpeakcanreachover0.9athigherlaboratory

flowvelocities[24].However,poorrecoveryandbreakthroughpeakatflowvelocities

approachingtothe4m/day(Tiraferri&Sethi,2009;Xin,Tang,Zheng,Shao,&Kolditz,2016).3.

Mixing:someofthecolumnstudiesintegratedmechanicalmixingintheirsetting[23],field

remediationisoftenconstrainedtointegratesuchfeature.However,carboxyl-methylcellulose-

basedandemulsioninducedNZVIhavesuccessfulacquiredadequateresultsatfieldflow

velocities[16][21].Full-scalefieldstudieswereconductedwiththetwoNZVIsuspensions;

however,unsuccessfulNZVItransportwasreported[11][22].

Theobjectiveofthisthesisistostudythemobilityofmicroemulsion-basedNZVIandtodevelop

anoptimizedsurfactant-basedNZVI.Chapter2and3inthisstudyaretwoscientificarticlesthat

criticallyexaminetwohighlystabilizedNZVIsurfacemodifiersontheirmobilityinporousmedia

andtheirpotentialtoafull-scaleremediation.

Page 13: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

5

Inchapter2,themobilityofmicroemulsion-stabilizedNZVIwithastabilityofover6months

developedbyWangetal.isaccessedusingironoxidenanoparticlesasastableanalogytoNZVI.

Highlyconcentratedmicroemulsionironnanoparticleswithidenticalcolloidalpropertiesto

microemulsionNZVIischaracterizedbysize,rheologyandstability.Laboratory1-Dcolumn

studyareconductedatdifferentconditionswithdifferentconcentrations,atlaboratoryand

fieldvelocitiesanddifferentsalinityenvironment.Thebreakthroughresultsaredemonstrated

andmodelledusingColloidFiltrationTheory(CFT).Excellenttransportresultswereobserved;

however,thehighsalinitysensitivityandthepropertyofthesurfactantimplythat

microemulsion-stabilizedNZVIisnotsuitableforafieldtest.

Inchapter3,basedontheimplicationsfromchapter2,anenvironmentalfriendlyphosphate

surfactant,isselectedasasurfactantstabilizer.Aframeworktodeterminethemoststable

nanoparticlessuspensionisadaptedfromWangetal.todeterminethemostoptimized

surfactant-basedNZVI.Itisimportanttonotethat,thusfar,nosophisticatedframeworkhas

beenappliedtodeterminetheformulationforaNZVIstabilizer.Theoptimizedsurfactant

yieldedastabilityofover2monthsandisexaminedwithalaboratory1-Dcolumnstudyatfield

velocity.Itisreportedthatthedevelopedformulationcanrecoverover90%ofNZVIwith

breakthroughpeaksat1.Itisexpectedthatthedevelopedphosphateformulationcanleadto

potentialfieldtestandeventuallyasuccessfulfieldapplication.

Itishypothesizedthattheprolongedstabilityobservedinthemicroemulsion-stabilizediron

nanoparticlesandsurfactant-stabilizedNZVIiscontributedbytheformationofwormlike

micellesinthesystems.Wormlikemicelles,asshowninfigure1.2,arelongandentangled

Page 14: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

6

aggregatesofmicellesthatdemonstratestructuresandproperties(suchasviscosity)similarto

polymers[27].Theformationofwormlikemicelleisdependentontheconcentrationofthe

surfactants,surfactantgeometry,curvaturesandpacking.Uponreachingtoacriticalassembly

concentration,themicellewillself-assembleintowormlikemicelles[28][29].Studieshave

suggestedthattheinteractionbetweennanoparticlesandwormlikemicellecanpromotethe

stabilityofthesuspension[27].

A.

B.

Figure1.2A.Schematicofwormlikemicelle,pictureprovidedbyMr.FrancisChoi[29]andB.

Page 15: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

7

theinteractionbetweenwormlikemicellesbyWangetal.andnanoparticles[27].

Overall,thisstudycontributedaphosphatesurfactantbasedNZVIsuspensionthatissuitable

forafieldapplicationbasedontheperformanceofmicroemulsion-basedNZVI.Thisstudyalso

suggestedthefeasibilityofmicroemulsionasatransportvehicleforinsituNZVIremediation.

Futurestudyon1.amoredetailedreactivitystudyofthephosphatesurfactantbasedNZVIand

2.TargetdeliverystudywithDNAPLinalargercolumnorsandboxarerecommendedpriorto

thefieldapplication.

Page 16: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

8

1.2Reference:[1] F.Fu,D.D.Dionysiou,andH.Liu,“Theuseofzero-valentironforgroundwaterremediationandwastewater

treatment:Areview,”J.Hazard.Mater.,vol.267,pp.194–205,2014.

[2] W.Wang,M.Zhou,Z.Jin,andT.Li,“Reactivitycharacteristicsofpoly(methylmethacrylate)coatednanoscaleiron

particlesfortrichloroethyleneremediation,”J.Hazard.Mater.,vol.173,no.1–3,pp.724–730,2010.

[3] M.Stefaniuk,P.Oleszczuk,andY.S.Ok,“Reviewonnanozerovalentiron(nZVI):Fromsynthesistoenvironmental

applications,”Chem.Eng.J.,vol.287,pp.618–632,2016.

[4] N.Saleh,T.Phenrat,K.Sirk,B.Dufour,J.Ok,T.Sarbu,K.Matyjaszewski,R.D.Tilton,andG.V.Lowry,“Adsorbed

triblockcopolymersdeliverreactiveironnanoparticlestotheoil/waterinterface,”NanoLett.,vol.5,no.12,pp.2489–

2494,2005.

[5] K.Moore,B.Forsberg,D.R.Baer,W.a.Arnold,andR.L.Penn,“Zero-ValentIron:ImpactofAnionsPresentduring

SynthesisonSubsequentNanoparticleReactivity,”J.Environ.Eng.,vol.137,no.10,pp.889–896,2011.

[6] W.ZhangandD.W.Elliott,“Applicationsofironnanoparticlesforgroundwaterremediation,”Remediat.J.,vol.16,no.

2,pp.7–21,2006.

[7] N.C.Mueller,J.Braun,J.Bruns,M.Černík,P.Rissing,D.Rickerby,andB.Nowack,“Applicationofnanoscalezerovalent

iron(NZVI)forgroundwaterremediationinEurope,”Environ.Sci.Pollut.Res.,vol.19,no.2,pp.550–558,2012.

[8] C.M.Kocur,A.I.Chowdhury,N.Sakulchaicharoen,H.K.Boparai,K.P.Weber,P.Sharma,M.M.Krol,L.Austrins,C.

Peace,B.E.Sleep,andD.M.O’Carroll,“CharacterizationofnZVImobilityinafieldscaletest,”Environ.Sci.Technol.,

vol.48,no.5,pp.2862–2869,2014.

[9] S.O’Hara,T.Krug,J.Quinn,C.Clausen,andC.Geiger,“FieldandlaboratoryevaluationofthetreatmentofDNAPL

sourcezonesusingemulsifiedzero-valentiron,”Remediat.J.,vol.16,no.2,pp.35–56,2006.

[10] D.O’Carroll,B.Sleep,M.Krol,H.Boparai,andC.Kocur,“Nanoscalezerovalentironandbimetallicparticlesfor

contaminatedsiteremediation,”Adv.WaterResour.,vol.51,pp.104–122,2013.

[11] A.I.A.Chowdhury,M.M.Krol,C.M.Kocur,H.K.Boparai,K.P.Weber,B.E.Sleep,andD.M.O’Carroll,“NZVIinjection

intovariablysaturatedsoils:Fieldandmodelingstudy,”J.Contam.Hydrol.,vol.183,pp.16–28,2015.

[12] E.M.Hotze,T.Phenrat,andG.VLowry,“Nanoparticleaggregation:challengestounderstandingtransportand

reactivityintheenvironment.,”J.Environ.Qual.,vol.39,pp.1909–1924,2010.

[13] S.Bettina,W.Hydutsky,andL.Bl,“DeliveryVehiclesforZerovalentMetalNanoparticlesinSoila

ndGroundwater,”vol.21,pp.2187–2193,2004.

Page 17: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

9

[14] F.He,D.Zhao,J.Liu,andC.B.Roberts,“StabilizationofFe-Pdnanoparticleswithsodiumcarboxymethylcellulosefor

enhancedtransportanddechlorinationoftrichloroethyleneinsoilandgroundwater,”Ind.Eng.Chem.Res.,vol.46,no.

1,pp.29–34,2007.

[15] B.Sleep,P.Mondal,P.Furbacher,Z.Cui,andM.Krol,“Transportofcarboxymethylcellulosestabilizednanoscale

zerovalentironinporousmedia,anexperimentalandmodelingstudy,”vol.17,p.7729,2015.

[16] C.M.Kocur,D.M.O’Carroll,andB.E.Sleep,“ImpactofnZVIstabilityonmobilityinporousmedia,”J.Contam.Hydrol.,

vol.145,pp.17–25,2013.

[17] P.Jiemvarangkul,W.X.Zhang,andH.L.Lien,“Enhancedtransportofpolyelectrolytestabilizednanoscalezero-valent

iron(nZVI)inporousmedia,”Chem.Eng.J.,vol.170,no.2–3,pp.482–491,2011.

[18] J.Soukupova,R.Zboril,I.Medrik,J.Filip,K.Safarova,R.Ledl,M.Mashlan,J.Nosek,andM.Cernik,“Highly

concentrated,reactiveandstabledispersionofzero-valentironnanoparticles:Directsurfaceandsiteapplication,”

Chem.Eng.J.,vol.262,pp.813–822,2015.

[19] N.Saleh,K.Sirk,Y.Liu,T.Phenrat,B.Dufour,K.Matyjaszewski,R.D.Tilton,andG.V.Lowry,“SurfaceModifications

EnhanceNanoironTransportandNAPLTargetinginSaturatedPorousMedia,”Environ.Eng.Sci.,vol.24,no.1,pp.45–

57,2007.

[20] Y.T.Wei,S.cheeWu,S.W.Yang,C.H.Che,H.L.Lien,andD.H.Huang,“Biodegradablesurfactantstabilizednanoscale

zero-valentironforinsitutreatmentofvinylchlorideand1,2-dichloroethane,”J.Hazard.Mater.,vol.211–212,pp.

373–380,2012.

[21] N.D.BergeandC.A.Ramsburg,“Oil-in-wateremulsionsforencapsulateddeliveryofreactiveironparticles,”Environ.

Sci.Technol.,vol.43,no.13,pp.5060–5066,2009.

[22] J.Quinn,C.Geiger,C.Clausen,K.Brooks,C.Coon,S.O’Hara,T.Krug,D.Major,W.S.Yoon,A.Gavaskar,andT.

Holdsworth,“FielddemonstrationofDNAPLdehalogenationusingemulsifiedzero-valentiron,”Environ.Sci.Technol.,

vol.39,no.5,pp.1309–1318,2005.

[23] H.I.Gomes,C.Dias-Ferreira,A.B.Ribeiro,andS.Pamukcu,“Enhancedtransportandtransformationofzerovalent

nanoironinclayusingdirectelectriccurrent,”Water.Air.SoilPollut.,vol.224,no.12,pp.1–12,2013.

[24] C.Mystrioti,N.Papassiopi,A.Xenidis,D.Dermatas,andM.Chrysochoou,“Columnstudyfortheevaluationofthe

transportpropertiesofpolyphenol-coatednanoiron,”J.Hazard.Mater.,vol.281,pp.64–69,2015.

[25] J.Xin,F.Tang,X.Zheng,H.Shao,andO.Kolditz,“Transportandretentionofxanthangum-stabilizedmicroscalezero-

valentironparticlesinsaturatedporousmedia,”WaterRes.,vol.88,pp.199–206,2016.

Page 18: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

10

[26] A.TiraferriandR.Sethi,“Enhancedtransportofzerovalentironnanoparticlesinsaturatedporousmediabyguargum,”

J.NanoparticleRes.,vol.11,no.3,pp.635–645,2009.

[27] M.E.Helgeson,T.K.Hodgdon,E.W.Kaler,N.J.Wagner,M.Vethamuthu,andK.P.Ananthapadmanabhan,“Formation

andrheologyofviscoelastic‘doublenetworks’inwormlikemicelle-nanoparticlemixtures,”Langmuir,vol.26,no.11,

pp.8049–8060,2010.

[28] A.Sambasivam,A.V.Sangwai,andR.Sureshkumar,“Self-AssemblyofNanoparticle-SurfactantComplexeswithRodlike

Micelles:AMolecularDynamicsStudy,”Langmuir,vol.32,no.5,pp.1214–1219,2016.

[29] X.Wang,D.S.Miller,E.Bukusoglu,J.J.DePablo,andN.L.Abbott,“Topologicaldefectsinliquidcrystalsastemplates

forMolecularSelf-Assembly,”Nat.Mater.,vol.15,no.September,pp.1–9,2015.

Page 19: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

11

Chapter2:TransportofMicroemulsion-StabilizedIronOxideinPorous

Media

Abstract

ThefullpotentialofNZVItechnologiesisoftenlimitedbythetransportNZVIparticlesthrough

porousmedia,whichinturnislimitedbythecolloidalstabilityoftheNZVIsuspension.Previous

workhasshownthatstableNZVIsuspensionscanbeproducedusingmicroemulsions(μEs)as

synthesis and suspensionmedia. In thiswork, Ironoxide nanoparticles, used as non-reactive

analogstoNZVI,wereusedtoevaluatethetransportintheμEusedtosynthesizeandsuspend

NZVI.Thetransportofthesesystemswasexaminedatfullstrength(10g/LFe)andasadiluted

(5g/L Fe) suspension using column studies. The nanoparticle injection protocol was also

evaluated(watervs.brineconditioning/rinsingfluid).Theresultingbreakthroughcurveswere

analyzed via a 3-compartment transport model that accounts for reversible and irreversible

attachmenttothesandpackedinthecolumn.Itwasdeterminedthatlargepressuredropswere

observedwithconcentratedsuspensions(10g/LFe),whichisexplainedbythelargeviscosityof

thesesystems.Thedilutedsuspensions(5g/LFe),havingalowerviscosity,couldbeinjectedin

thesystem,producinghighparticlerecoveries(~90%)whenthesolutionusedtoconditionand

rinsethecolumnwasabrinewiththesamesaltconcentrationastheμE.However,whenusing

deionizedwatertoconditionandrinsethecolumn, lowerrecoveries (~60%)wereobtained,

likelyduetophasetransitionsintheμEthatresultedinthedepositionofparticles.

Page 20: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

12

2.1Introduction

Nanoscalezero-valentiron(NZVI)particlesareeffectivereducingagentsforavarietyof

contaminants,includingheavymetals,dyes,chlorinatedorganiccompounds,aromaticand

arsenic-containingcompounds[1][2].ThenanoscalesizeofZVIparticles,rangingfrom10to

200nm,yieldshighsurfaceareasandthusincreasedcontactwiththecontaminantsmakingthe

reductionreactionsmoreefficient[3].NZVIcaneffectivelyreducecommoncontaminantssuch

astrichloethylene(TCE)toethylenewithindaysorweeks[1][4][5][6].NZVIinjectionhasshown

promiseintreatingcontaminantsinnumerousfield-scalestudiesconductedinEuropeand

NorthAmericainthelastdecade[7][8][9].

NZVIaquiferremediationisstillhinderedbythelimitedcolloidalstabilityofsuspensions

currentlyinuse,resultinginrapidaggregationandsettling[8][9][10][11][12].Therapid

aggregationandfastsettlingfeatureofNZVIiscausedbythehighsurfacemagneticpotential

[4][13].Duringthetransport,aggregatedNZVIaremorelikelytoexperiencefiltrationbythe

sandporesduetothelargesize.Settlingofaggregatedparticlesalsocontributetothe

depositionofNZVIontheporousmedia[13].Schricketal.andTiraferietal.reportedthatpoor

transportperformanceofunstableNZVIareobservedinlaboratorycolumnstudiesat

consideratelylowconcentrations(0.05-0.1g/L)[10][14].

TheintroductionofthesurfacemodificationscanreducetheaggregationofNZVIparticlesand

thuscontributetoimproveNZVItransportinporousmedia[10][15][16].Inspecific,surface

modificationsareservedassurfacestabilizers,theycreatedanenergybarrierintheNZVI

suspensiontokeeptheparticlesfromattractingandaggregating.Commonsurfacemodifiers

Page 21: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

13

includeemulsions,anionicsurfactants,polymers,organicacidsandpolymericsurfactants[4]

[7][16][12][17][18][19][20].

Laboratorystudiesandfieldtrialshavereportedsomeprogressinimprovingthemobilityof

NZVIinsoil;however,theaggregationofNZVIhasnotbeenfullyaddressed[17][19][21][22].

MostofthestabilizedNZVIcolumnstudies,suchasthoseconductedusingxantumgum-

stabilizedNZVIandpolyphenol-stabilizedNZVIreportedhighNZVIrecovery,over85%,atpore

velocitiesbetween20-200m/daywhileonly10%tonegligiblerecoveryobservedatvelocities

below10m/day[22][23][17][24][25].O’Carrolletal.andKocuretal.indicatedthattypical

injectionvelocitiesforafield-scalein-situremediationrangebetween0.25and4m/day

[20][19][18].Thehighrecoveryreportedbymosttheliteraturestudiesareanoptimistic

estimationoftheabilityofthesurfacestabilizersapplied.Stabilizersthatallowadequate

transportofNZVIatlowporevelocitiesarestillneeded.

ColumnstudiesconductedbyBergeetal.andKocuretal.withemulsionNZVIand

carboxylmethyl-cellulose(CMC)NZVI,respectively,reportedNZVIrecoveriesof90%for

injectionvelocitiesrelevanttofieldapplications[19][26].ItwasreportedthatemulsionNZVIis

kineticallystableandCMCNZVIholdsarelativelyhighstabilityof80hours[7][19].However,

thefieldresultsintheCMCNZVIimpliedthatastabilityof80hoursmaynotbesufficient.In

2014,Kocuretalconductedafield-scaleremediationwithCMCNZVIatasiteinSarnia[2].CMC

stabilizedNZVIat1g/Lironconcentrationwasinjectedatgroundwaterflowvelocitiesof0.02-

0.8m/dayusinggravityinjection.After10daysofcontactingperiod,CMCNZVIwasobservedat

monitoringwells1meterdownstream,implyingthattheminimumtransportdistanceofCMC

NZVIisatleast1meter.However,therecoveryoftheinjectedNZVIwasonly1%[27].Similar

Page 22: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

14

findingswerereportedintheemulsionNZVIfieldstudy[10].Additionally,fielddemonstrations

ofNZVIremediationreportedshorttraveldistancesbetween0.5to2.4meters[19][28].

Furthermore,someofthereportedNZVIcolumnstudiesrequiredcontinuousmechanical

mixingtopreventNZVIfromsettlingintheinjectionpoint[17].Mechanicalmixingmightbe

impracticaltoscaleup.TheseobservationsshowthatdespitetheimprovedstabilityofNZVI

suspensionbystabilizers,thedelayedaggregationmechanismwasnotfullyeliminated.

O’Carrolletal.suggestedthatanidealNZVIformulationshould:(1)maintainstabilitysuchthat

theparticlesdonotaggregateandsettle;(2)musthaveahighconcentrationofironwhile

maintainingasmallsize;(3)sustaincertainamountofmobilitywhilebeinginjectedinsoil[19].

ThemostsuccessfulsystemsthusfarareCMCNZVIandbimetallicNZVI[27][28].Despitegood

remediationresults,allthefieldscalestudiesofNZVIreportedthatlittletonoNZVIparticles

wererecovereduponcompletion,implyingimmobilizationandemphasizingtheneedforbetter

transportoftheparticles.

Wangetal.introducedtheuseofmicroemulsions(μEs)asbothsynthesissolventand

suspendingmediainaone-potsynthesisprocedure[29].μEsarethermodynamicallystable

systemscontainingoiland/orwaternano-domains(typicallyof10to100nm)thatare

stabilizedbysurfactant(s)adsorbedattheoil-waterinterface.TheformulationoftheμE-based

synthesis/suspensionmediawasdesignedviatheHydrophilic-Lipophilic-Difference(HLD)

framework,usedbyChoietal.andWangetal.todeterminethecombinationofsurfactant,

electrolyte,oil,andtemperaturethatproducesbicontinuousnet-zerocurvaturesystems

(whereHLD=0),whichalsoleadstotheformationofsuspensionsthatarestableforseveral

months,andareeasilyre-suspendedwithmildmixing[16][29][30].

Page 23: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

15

DespitetheadvancesmadewithμEsynthesis/suspensionmediaforNZVI,nostudieshavebeen

conductedtovarytheirtransportthroughporousmedia.Microemulsionsontheirownhave

beenappliedaspartofthesurfactantenhancedrecoveryremediation[31].Thesurfactant

enhancedaquiferremediation(SEAR)hasbeensuccessfullyappliedfortheremediationof

mediumtolowdensitynon-aqueousphaseliquids(LNAPLs),butdownwardmobilizationofhigh

densityplumesofchlorinatedsolvents(DNAPLs)havelimitedtheiruseforthoseapplications

[32].

Inprinciple,μE-NZVImeetsthestandardsrequiredforanidealstabilizer,buttheireffectiveness

havenotbeenevaluatedviacolumnstudies.Thus,itistheinterestofthisworktoexaminethe

transportpropertiesofμE-NZVIinone-dimensional(1-D)columnstudiesandassessits

potentialusefulnessinfieldapplications.

Forthepurposeofanalyzingtheintrinsicabilityofmicroemulsionasatransportvehicle,iron

oxideisusedinthisresearchasananalogytoNZVI[13][16][33][34].Microemulsionironoxide

developedbyChoietal.hasidenticalcolloidalstructureandsizetoμE-NZVI[30].Inadditional,

ironoxideisusedasasynthesisbasistoproduceNZVIinsomecasesandcanbecategorized

withNZVIintermsofenvironmentalapplication[34][35].Transportofironoxideinporous

mediaisalsointerestofenvironmentalandbiomedicalresearch.

TheobjectiveofthisworkistodetermineandassessthepotentialandabilityofμEsasastabilizer

and delivery vehicle for NZVI in porousmedia using iron oxide nanoparticles as analog. The

studieswereconductedusingfield-relevantconditionsthatmosttheothercolumnstudiesdon’t

typically consider: high concentration of suspended iron and a low Darcy velocity. Several

preliminary and post analytical strategies including size determination using dynamic light

Page 24: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

16

scattering(DLS)andTEM,viscositytestandparticlecolumndistributionareconductedtoprovide

a better understanding on the filtration mechanism between the porous media and the

nanoparticles.Colloidfiltrationtheoryisusedtodescribeandestimatethetransportefficiency

anddistanceofthemicroemulsionironoxide.Theresultofthispaperimpliedandcontributed

thepotentialofanewandefficientsurfacemodificationtechniqueforNZVIinsituremediation.

2.2Methodology

2.2.1SynthesisofMicroemulsionIronOxide

Microemulsionironoxidesuspensionwassynthesizedbybatchfromtheproceduredeveloped

byChoietal.[30]:0.103gramsironoxidenanoparticles(purchasedfromSigmaAldrich,

98%,No.637106),0.327gramsfoodgradeoilethylcaprate(purchasedfromSigma

Aldrich,98%,No.W243205),2.976mLsurfactantAlfoteraK3-4SC10H21O(CH3CH2(CH3)O)4SO4Na

(donatedbySasolNorthAmerica,32.5wt%,lotno.4130115),3.23mLNaCl(Bioshop,Reagent

Grade,SOD002.205)brinesolution(30g/100ml)and3.47mLwater.Thechemicalswere

addedbyweightusinganelectronicscale(DenverInstrumentXX7020023AnalyticalBalance

LabScale±0.0001g)andbyvolumeviapipettingwithanautomaticpipet(FisherBrand,Elite,

AdjustableVolumePipetter,0.5-5mL).Theformulationmixturewasmixedusingavortexer

(VWR,minivorterxer,WM-3000)at5,000rpmfor1minuteandsonicateusingasonicatorbath

(Cole-Parmer,8891)for1minute.Themixingtagewastoensurefullandevensuspensionof

thenanoparticles.Thecompletedsuspensionyieldedabrowncolouruniformly.Eachbatchof

theironoxidesuspensionprovides10mlof10g/Lironoxide(equivalentto7g/LFe)

suspensionwithasalinityof10gNaCl/100ml(10%NaClbrine).FormakingμEironoxide

suspensionwithlowerconcentrationat5g/Lthe10g/Lformulationwasdilutedwith10%NaCl

Page 25: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

17

brinesolution(10g/100mL).Keepingthesamesalinityensuredthattheformulationretained

itsstructure,thuspreventinganyphasebehaviorchange.Itisimportanttonotethatforthe

purposeoftrackingthetransportofμE,solventbluedye(Sigma-aldrich,98%,17354-14-2)was

dissolvedinethylcaprateataconcentrationof5000ppm.

2.2.2Determiningthestabilityofmicroemulsionironoxide.

Todeterminethestabilityofmicroemulsionironoxide,timelapsephotosoftheironoxide

formulationsandbareironoxideweretakenoveraperiodof1year.Thetimelapsephotos

weretakendailyinthefirstmonth,bi-weeklylaterandmonthlyfortheremainingperiod.The

collectedphotosofthesampleswereanalyzedvisuallyforsignsofaggregation,settlingand

instability.

2.2.3Viscositystudyofmicroemulsionironoxideformulations

TodeterminetheviscosityoftheμEsandtheironoxide–loadedμEsarheometer(TA

instrument,CSL2500)wasused.Theviscositiesweremeasuredatdynamicshearrates

increasingfrom3-500(1/S).

2.2.4Sizecharacterizationofmicroemulsionironoxideandmicroemulsionformulations

Transmissionelectronmicroscopy(TEM,HitachiHF-3300)wasusedtoassessthesizeandstate

ofaggregrationoftheironnanoparticlesin5g/Lsuspensions.ItisimportanttonotethatTEM

imagingwasnotabletocapturetheμEcomponentsofthesuspension,onlytheiron

nanoparticles.Dynamiclightscattering(DLS)measurementswereconductedonμEironoxide

at5and10g/LusingaBrookhavenParticleSizeAnalyzer90Plus.Priortosizeanalysis,the

sampleswerediluted50timeswith10%NaClbrine.

Page 26: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

18

2.2.5Columnstudy.

Twosetsofcolumntransportexperimentswereconductedwithsimilarproceduresand

identicalsetupforanalyzingthetransportatdifferentflowconditions.Thesetupofthecolumn

experimentsisshowninFigure2.1.Inshort,theconditioning/rinsingfluidandμEironoxide

wereinjectedwithaperistaticpump(ColeParmer,MasterFlexL/S)inanupwarddirectionand

wereswitched,asneeded,viaathree-way-valve.Theflowpassedthroughapressuregaugefor

pressuredropmonitoringbeforeenteringthesandcolumn.Theeffluentfromthecolumnwas

collectedbyafractioncollector(RediFrac,BioscienceAmersham).

Thefirstsetsofcolumnexperimentswereconductedwithaglasscolumn(1.0x15cm,Kontes

ChromaflexColumns,KimbleChase,Vineland,NJ.)havinganaspectratioof15andthesecond

setofcolumnexperiments,wereconductedwithalargerglasscolumn(2.5x15cm,Kontes

ChromaflexColumns,KimbleChase,Vineland,NJ.)withidenticallengthbutbiggerinner

diameter,thusaloweraspectratioof6.Bothcolumnswerewet-packedhomogeneouslywith

acidwashedOttawasand(FisherScientific,~500micrometersinradius)and1wt%Alfoterra

K3-4Ssurfactantsolutionusedtoremoveairpocketstrappedinthesandmedia.Theweightof

thecolumn,sandandamountofsolutionweremeasuredwithanelectronicbalance(Denver

Instrument,TP-214)beforeandafterthepackingprocess.Themeasuredweightswereusedin

massbalancetodeterminetheporevolume.Itwasdeterminedthatsmallandlargecolumns

have4.7and30.2mLporevolume,respectively.

Page 27: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

19

Figure2.1Columnexperimentconfiguration

Thefirstsetsofcolumnexperimentswereconductedwithaglasscolumn(1.0x15cm,Kontes

ChromaflexColumns,KimbleChase,Vineland,NJ.)equivalenttoanaspectratioof15andthe

secondsetofcolumnexperiments,wereconductedwithalargerglasscolumn(2.5x15cm,

KontesChromaflexColumns,KimbleChase,Vineland,NJ.)withidenticallengthbutbiggerinner

diameter,thusaloweraspectratioof6.Bothcolumnswerewet-packedhomogeneouslywith

acidwashedOttawasand(FisherScientific,~500micrometersinradius)with1wt%K3-4S

surfactantsolutionforeliminatingairpocketstrappedinthesandmedia.Theweightofthe

column,sandandamountofsolutionweremeasuredwithanelectronicbalance(Denver

Instrument,TP-214)beforeandafterthepackingprocess.Theweightsoftheabovewereused

inmassbalancetodeterminetheporevolumes.Itisdeterminedthatsmallandlargecolumn

holda4.7and30.2mLofporevolumes,respectively.

Forexperimentsconductedwiththesmallcolumn,10porevolumesofconditioningsolution

werepumpedfromthebottomofthecolumnbyaperistaticpump,thisisknownasthepre-

flushingorconditioningstage.Theperistaticpumpwasoperatingat0.5mL/minequivalenttoa

Page 28: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

20

Darcyvelocityof20m/dayandforalowervelocityasyringepump(notshowninFigure2.1)

wasusedtoproduceaDarcyvelocityof5m/day.Duringtheconditioningstage,thepressure

dropwasrecordedeveryporevolume.Brine(10%NaCl)solutionwasusedastheconditioning

fluidtokeepthesalinityconsistentwiththeμEironoxideformulation.Aftertheconditioning

stage,thepressuregaugewasbypassedtoavoidμEentrainmentinthepressuregaugeline.A

totalof1.5porevolumesofμEironoxideatconcentrationsof5or10g/L(asironoxide)were

injectedtothecolumn.Thefractioncollectorwasthenstartedandsettocollect3minutesof

flowpersample(i.e.1.5mL/sample)forthehigherDarcyvelocityand5minutes/sample

(0.5mL/sample)forthelowerDarcyvelocity.Uponthecompletionoftheironoxideinjection,

another10porevolumesofthesamesolutionusedduringtheconditioningstagewerethen

introducedintothecolumnasarinsingstep.Thecollectionofsampleswasstoppedattheend

oftherinsingstage.

ThesamplescollectedwereanalyzedviaaciddigestionwithHCl6N(BDH,BDH7204-1)witha

sampletoHClvolumeratioof1:14.5,aspertheprocedureofRadetal.[1].Theaciddigested

ironoxidesampleswereanalyzedunderUV-VISspectrometer(80-2092-26,LKBBiochrom

England)at398nmafterareactionperiodof3days.Acalibrationcurvewascreatedusingthe

μEironoxidesuspensioninjectedintothecolumn.

Forthelargecolumn(aspectratioof6),experimentswereconductedat5m/day.Inthese

experiments,twoconditioning/rinsingscheduleswereevaluatedassummarizedinFigure2.2.

ScheduleA,inFigure2.2,followsthesameconditioning/rinsingstepsusedwiththesmall

columnwhere10%NaClwasusedastheconditioning/rinsingsolution.InScheduleBstudies,

deionizedwaterwasusedastheconditioning/rinsingsolvent.ScheduleAisbeneficialbecause

Page 29: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

21

itmaintainstheionicstrengthofthemicroemulsion,reducingthechangesforphasechanges.

ScheduleBrunstheriskofμEphasechanges,butitslowionicstrengthismoreconsistentwith

thatofgroundwater.Uponcompletionoftheconditioningstage,1.5porevolumesofμEiron

oxidesuspensionscontaining5and10g/L(asironoxide)wereinjectedintothecolumn.The

fractioncollectorwassetto3min/sample(1.5ml/sample).Fractionalcollectorsettingat3

min/sample(1.5ml/sample)wasusedtocollectthesample.Thecollectedsampleswerethen

analyzedforironcontentusingtheaciddigestionprocedurepreviouslydescribed.Afterthe

rinsingstep,thesandinthecolumnwascollectedanddividedintofivesegments,eachbeing

approximately3cminlengthtodeterminetheresidualirondistributionleftonthecolumn.The

irondistributionanalysiscombinedmicroscopeimagingandaciddigestionsofsandataweight

ratioof0.3gofsandto3mLofHCl6Nacid.Finally,selectedeffluentsamples,correspondingto

thepeakofthebreakthroughcurve,wereanalyzedunderDLStoassesspotentialparticle

aggregation.

Figure2.2Injectionscheduleofthecolumnstudies.

Page 30: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

22

2.2.6.BreakthroughCurveModeling.

Aswillbediscussedlater,thebreakthroughcurvesobtainedinthisworkhavefeatures

characteristicofthreedifferentphenomena;diffusion/dispersion,reversible

“chromatographic”adsorption,andtheirreversible“attachment”orfiltrationofparticles.To

representthesefeatures,Figure2.3presentsa3-compartmenttransportmodel.

Figure2.3Schematicofthethree-compartmentmodelusedtorepresentthereversible

adsorptionofparticle,advection/dispersioncolumntransport,andparticleattachment.

Thecentralcompartmentcorrespondstothetransportoftheparticlesthroughthecolumn,

withmassbalanceequation:

Ci,t-1Ci-1,t-1

Crev i,t-1Crev i-1,t-1

Catti,t-1Catti-1,t-1

Ci+1,t-1

Crev i+1,t-1

Catti+1,t-1

Flow

Ci,tCi-1,t

Crev i,tCrev i-1,t

Catti,tCatti-1,t

Ci+1,t

Crev i+1,t

Catti+1,t

Flow

Time“t-1”

Time“t”

Page 31: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

23

!"!#= −𝑣 !"

!(+ 𝐷 !+"

!(+− 𝑘-##𝑐 − 𝑓012

!"345!#

(1)

Where“C”istheconcentrationoftheparticleatagiventime“t”andasectionofcolumn“i”,

andwouldcorrespondtothevariableCi,tintheschematicofFigure2.3.Theterm“v”isthe

pore(Darcy)velocity,“D”istheeffectivediffusivityoftheparticlesinthecolumn.Itshouldbe

clarifiedthatthisdiffusivityincludesback-mixingordispersioneffectsinthecolumn,beyond

theintrinsicdiffusivityoftheparticles.Thevariable“z”isthecolumnlengthaxis,represented

bythecolumnlocationindex“i”inFigure2.3.Theparameterkattisusedtorepresentthe

particleattachmentprocessasafirstorderirreversiblereaction,inasimilarwaythatthe

colloidfiltrationtheorydoes[36][37].

Thereversibleadsorptioncompartmentisusedtoaccountforthesametypeofreversible

exchangethattakesplaceinchromatographicseparation[38][39].Inthecolumnstudies,this

reversibleexchangeresultsin“tailing”effectsinthebreakthroughcurvethatcannotbe

simulatedwiththediffusivity(dispersion)term.Asitwillbeshownintheresultsection,such

tailingeffectsareobservedinourresultsandotherresultspresentedintheliterature.To

considerreversibleadsorption,Figure2.3presentsamathematicalconstructionofa

compartmentwithanequivalentvolume“Vrev”wheretheconcentrationoftheparticlesis

“Crev”.Theterm“frev”istheratiobetweenthevolumeofthereversibleadsorption

compartmentandthevolumeofthecolumn(frev=Vrev/V).Themassbalanceoftheparticlesin

thereversiblecompartmentis:

!"345!#

= 𝐾 78 012

𝑐 − 𝑐012 = 𝑘012 𝑐 − 𝑐012 (2)

Page 32: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

24

whereKcanbeinterpretedasthemasstransfercoefficientinbetweenthecolumnandthe

reversiblecompartment,andA/Vcanbeinterpretedasthesurfaceareatovolumeratioforthe

transportintothereversiblecompartment.TheoveralltermK*A/Vresultsinafirstorder

constant,krev.ItmustbeclarifiedthatthesimplemasstransportexpressionofEquation2

impliesalinearadsorptionbehavior.Morecomplexadsorptionbehavior,suchasLangmuir

adsorptioncouldbeused,butaswillbeshownlater,thesimplemodelofEquation2was

enoughtoreproducethetailfeaturesofthebreakthroughcurves.

Finally,themassbalancefortheirreversiblyadsorbed(attached)particlecompartmentis:

!9:;;!#

= 𝑉-##!":;;!#

= 𝑉𝑘-##𝑐 (3)

Asinthecaseofthereversibleadsorption,theirreversibleparticleattachmentcompartmentis

amathematicalsimplificationofanequivalentcompartmentofvolume“Vatt”,aspresentedin

Figure2.3.Theuseofthereversibleadsorptionandattachmentcompartmentssimplifiesthe

numericalsolutionofthemassbalancesandavoidsintroducingpartitioncoefficientsor

adsorptionisothermsthatwouldintroducemorefittingparameters.

Tosolvethedifferentialequations,finitedifferencesintime(t)andspace(z)were

implemented,asillustratedinFigure2.3.Theinitialtime-baseconditionwasallthe

concentrationsinthethreecompartmentsbeingzeroattimezero.Theinitialspace-base

conditionwasintroducedinawaythatitrepresentedtheinjectionprotocol,inotherwords,C0,t

Page 33: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

25

=Co(feedconcentration)foraslongastheinjectionoccurred,andzerootherwise.Thenon-

dimensionalfinitedifferenceformsofthebalanceequationsare:

𝐶012#,?∗ = 𝐶012#AB,?∗ + 𝑘012∗ 𝐶#AB,?∗ − 𝐶012#AB,?∗ 𝛥𝑡∗ (4)

𝐶#,?∗ = 𝐶#AB,?∗ − 𝐶#AB,?∗ − 𝐶#AB,?AB∗ ∆#∗

∆(∗+ 𝐷∗ ";FG,HIG

∗ A";FG,H∗

∆(∗− ";FG,H

∗ A";FG,HFG∗

∆(∗∆#∗

∆(∗− 𝑘-##∗ 𝐶#AB,?∗ ∆𝑡∗ − 𝑓012 𝐶012#,?∗ − 𝐶012#AB,?∗ (5)

𝑚-###,?∗ = 𝑚-###AB,?

∗ + 𝑘-##∗ 𝐶#,?∗ ∆𝑡∗ (6)

wherealltheconcentrationtermsarenormalizedbytheinitialconcentration(C*=C/Co),the

subindex“t”representthesolutionatagiventime,and“t-1”representsthesolutioninthe

previoustimestep.ThedimensionlessintervaloftimeisΔt*=Δt/τ,where“τ”istheresidence

timeinthecolumn.Thedimensionlessreversibleadsorptionrateconstantisk*rev=krev·τ.The

dimensionlessintervalofspaceisΔz*=Δz/L,where“L”isthelengthofthecolumn.The

dimensionlessdiffusioncoefficientisD*=D·τ/L2.Thedimensionlessattachmentrateconstantis

k*att=katt·τ.Thedimensionlessattachedmassismatt*=matt/(V·Co).

ThesefinitedifferenceequationsweresolvedinExcel,usinganspatialstep,Δz*=Δz/L=0.01,

andantemporalstepΔt*=Δt/τ=0.005.

Theattachmentconstant,katt,canbeusedincolloidfiltrationtheorytoestimatethedistance

towhich1%oftheinitialparticles(Lmax)arestillpresentinthefluid,usingtheequation[2]:

𝐿9-L = − 2M:;;

ln(0.01) (7)

Usingthesingle-collectorcontactefficiency(ηo)correlationdevelopedbyTufenkjietal.[37],

onecanassesstheattachmentefficiency(α),usefultocomparetoothercolumn

Page 34: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

26

studies[10][19][20][21][40]:

𝑘-## =U(BAV)WXYZ

𝜂\𝛼𝑣 (8)

Inequation8,𝜖representstheporosityofthesystemand𝑑`arepresentstheaveragegrainsize.

Consideringv=4m/day,d50=0.5mm,𝜂\~0.0005fromthecorrelationofTufenkjietalusinga

Hamakerconstantof1E-19J,a270nmparticleandafluidwith250cPviscosity[3].Aswillbe

shownlater,thesearetheconditionsthatapplytothecolumnstudiescarriedoutwithdiluted

μEsystemscontaining5g/Lironoxidenanoparticles.

2.3ResultsandDiscussion

2.3.1StabilityTest.

Figure2.4showsthetimelapsephotosofbareironoxide,μEironoxideat10g/Land5g/L

(Dilutionratio1:1withNaClbrinesolution(10g/100ml))overaperiodof1year.Asexpected,

thebareironoxidesuspensiondisplayedcolloidalinstability,settlingsoonaftermixingasseen

inFigure2.4(c).Bareironoxidenanoparticlessettledwithin10minutes.Incontrast,theμE-

stabilizedironoxideformulationsattheoriginalconcentrationof10g/Landatthediluted

concentrationof5g/Lremainedasasinglephaseafter1year.Visualinspectionindicatedno

signsofaggregationandsettlingbehaviour,asshowninFigure2.4.Theprolongedstability

demonstratedbytheμEironoxideisconsistentwithμENZVIasreportedbyWangetal.[29].

Thesimilarityinthehighstabilitybetweenthetwosuspensionsemphasizesthesimilarity

betweenthetwotypesofsuspensions.Thecompellingstabilitydemonstratedbythe

microemulsionironoxideformulationmatchedtherequirementsproposedbyO’Carroll,as

mentionedpreviously,inferringtraitsofgoodNZVI/ironmobilityinsoil.

Page 35: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

27

Choietal.proposedthatinsystemsthattendtoformbicontinuousμEs(thecaseforthe

formulationconditionsusedhere,andthoseofWangetal.),butwhoseextremelylowoil/water

ratiodoesnotallowtheformulationofbicontinuousstructures,worm-likemicellesareformed

instead,producinganetworkcapableofsuspendingnanoparticles[30].Theobservedstability

observedwithμEironoxidenanoparticlesaresubstantiallylongerthanonethemostsuccessful

NZVIsurfacestabilizations(about80hourswithCMC)[19][18][34].

Figure2.4TimelapsephotocomparisonsofμEironoxideandbareironoxide:(A)10g/LμE

ironoxide.(B)5g/LμEironoxide.(C)10g/Lbareironoxidenanoparticles

2.3.2RheologicalProperties.

Figure2.5showstheviscosityvs.shearratefortheoriginalμEformulationandthe50%diluted

formulation,with(topFigure)andwithout(bottomFigure)ironnanoparticles.Fromthegraphs

inFigure2.5,theviscositydecreaseswithanincreaseinshearrate,confirmingashear-thinning,

non-NewtonianbehaviourforbothμEandμEironoxide.TointerprettheresultsofFigure2.5,

oneneedstoconsiderthattheshearrate(γ̊~v/d50)foracolumnoperatingataporevelocity

ofv=5m/dayandparticlesized50=0.5mm,thentheshearrateisintheorderof0.1s-1.The

Page 36: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

28

viscositiespresentedinFigure2.5areforhighershearrates,butextrapolatingthepowerlaw

functionstotheexpectedshearrate,γ̊~0.1s-1,thentheviscosityforthefullstrengthiron

oxide(10g/LFe2O3)μEsuspensionwouldbecloseto1200cP,andforthedilutedsuspension

(5g/LFe2O3)wouldbecloserto250cP.FortheμEalone(withoutironoxide),theviscosity

seemtoplateaucloseto200cPatlowshearrates.TheviscosityforthedilutedμE(withoutiron

oxide)atashearrateof0.1s-1isexpectedtobearound30cP,andthelowvalueofthe

exponentofthepowerfunctionsuggeststhatthebehaviorofthisparticularsystemiscloserto

thatofaNewtonianfluid.AtleastforthedilutedμEsystems,isclearthattheadditionof

nanoparticlesproducedanincreaseintheviscosityofthesystem.

TheviscosityofthesurfacemodifiednZVIsuspensionsisidentifiedasacriticalvariablethat

mayinfluencethetransportintheporousmediaandmobilizationofDNAPL[2][8][19][27].The

trendsinchangesinviscositywithchangesinconcentrationandparticleadditionobservedin

thisstudyareconsistentwithotherstudiesonemulsiontransportinporousmediaForthecase

ofpolymer-suspendednanoparticles,suchasCMCNZVI,increasingtheNZVIparticlecontent

doesnotinfluencetheviscosityofthesolution[19][41].AμEviscosity,atabout100-1000cP

dependingonthedilution,wasalsolargerthantheviscosityofCMCNZVI,atabout10-50cP

[19].TherelativelyhighviscosityoftheconcentratedμEironoxidemayhinderμEironoxide

transportthroughporousmediaandmaycontributetohighpressuredrop,asobservedinO/W

emulsiontransportstudies[42].

Page 37: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

29

(a)

(b)

Figure2.5Viscosityprofilegraph(logscaled)ofμEironoxide(a)andME(b),comparison

betweentheoriginalformulationsanddilutionwithNaClbrinesolution(10g/100mL)at1:1

ratio.

y=0.4784x-0.432

y=0.1128x-0.366

0.001

0.01

0.1

1

10 100 1000

Viscosity

Pa.s

ShearRate(1/s)

MicroemulsionFeo10g/LMicroemulsion5g/L

y=0.0204x-0.191

y=2.0728x-0.594

0.001

0.01

0.1

1

10 100 1000

Viscosity

Pa.S

ShearRate(1/S)

50%DilutionNoDilution

Page 38: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

30

2.3.3SizeCharacterization.

Figure2.6demonstratestheapproximatesizerangeofμEironoxideandμENZVIunderTEM.

TheTEMimaginggivesinformationaboutthesizeofindividualparticlesandparticleclusters,

butitisnotsuitabletoindicatethesizeofoil-swollen-micellesadsorbedonthenanoparticles.

Analternativetechniquewouldhavebeentousecryo-TEMthatcouldillustratetheinteraction

ofmicelles(presumablyworm-likemicelles)andthenanoparticles.However,thattechnique

wasnotavailableinourfacilities.Figure2.6thatμENZVI-stabilizedironoxideparticlesarein

therangeof50to100nm,whichconfirmingthesimilarityinsizewithμENZVIbyWangetal.

Sincedynamiclightscatteringcanmeasurethehydrodynamicradiusoftheironoxideparticles

withinthemicellesystem,abetterdescriptionoftheaggregatesizecanbeobtainedviaDLS

measurements.ThemeasureddiameterofμEironoxideat10g/Lis270+/-10nm,this

measuredsizefellwithintherangeofestimatedoptimaltransportofNZVIandabouthalfthe

sizeofCMCNZVI[2][4].SizemeasurementswerealsoconductedtotheμEironoxideeffluent

fromthelowaspectratiocolumn,findinganaggregatesizeof530+/-70nm.Similarresults

werealsoobtainedwithμEironoxideat5g/Lsystem.Eventhoughthesizeofthe

nanoparticlesalmostdoubleduponelutionfromthecolumn,thesizesarestillconsideredinthe

optimalrange.SimilaraggregationeffectshavebeenobservedinthecolumneffluentofCMC

NZVIstudies[2][4].

Page 39: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

31

(a)

(b)

Figure2.6TEMimagingofMicroemulsionironoxideat5g/Lwith100nmasscale(a)and

microemulsionNZVIat1g/LbyWangetal.

2.3.4μEIronOxideTransport

Figure2.7presentpicturesofthecolumnstudies(1cmx15cmcolumn)obtainedwithμEiron

oxidesuspensionscontaining10g/L(left)and5g/L(right)Fe,whentheporevelocitywas5

m/day.The10g/Lsystemshowsaclearaccumulationofironinthebottomhalfofthecolumn.

Page 40: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

32

Atthatpoint,theflowwasstoppedbecauseofthelargepressuredropobtainedwiththis

system(morethan100inchesofwater).Thepictureontheleftshowstheironcompletely

distributedthroughoutthecolumnafterthefirstporevolumebrokethroughthecolumn.As

indicatedintherheologicalstudies,thelargeviscosity(1200cP)couldbethereasonforthe

largepressuredrop.OnecanusetheKozeny–Carmanequationtoestimatethepressuredrop

forapackingofsmoothmonodispersespheres[43]:

∆𝑃 = (BAV)+BcadV+XYZ+

𝑣 ∙ 𝐿 (9)

Usingaporevelocity(v)of5m/day,aviscosity(μ)of1200cP,aparticlediameter(d50)of0.5

mm,abedporosity(ε)of0.35,acolumnlength(L)of15cm,thepressuredropshouldhave

been104”water.AlthoughthisisconsistentwiththepressurereportedinTable2.1,the

pressurewassubstantiallylargerthan100”water.Evenafterbypassingthepressuregauge,no

flowcouldbeinjectedthroughthecolumn.Itispossiblethatchangesinthestructureofthe

worm-likemicellesystemcouldhaveledtochangesinviscosityintheleadingedgeoftheμE

suspensionfrontincontactwiththeconditioningphase(a10%NaClbrineforthesystemsof

Figure2.7).Infact,accordingtoChoietal.[30],wormlikemicellesproducedwithsuspensions

similartothoseusedinthisworkdisplaygel-likepropertiesatlowenoughshear.

Page 41: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

33

a. b.

Figure2.7Transportofironoxidesuspensionsin1-cmdiameter(highaspectratio)columnat5

m/dayporevelocity(a)10g/Lironoxide(b)5g/Lironoxide.

Toovercomethegel-likebehavioratlowshearrateforthe10g/Lsystem,theporevelocitywas

increasedto20m/day.Thisincreaseinvelocitydisruptedthegel-likestructureformedwiththe

10g/Lsystem,allowingtherecoveryof60%ofironoxide,asindicatedinTable2.1.However,

porevelocitiescloserto5m/dayarepreferred,closertotheporevelocitiesusedinaquifer

remediation.Tomaintainaporevelocityof5m/day,thediluted5g/Lsuspensionwas

consideredfortherestofthestudies.Figure2.8presentsthebreakthroughcurvesobtained

withthe5g/Lsuspension,injectedat5m/day,usingcolumnswithaspectratioof15(1cmx

15cm)and6(2.5cmx15cm).The3-compartmentmodelparameterscorrespondingtothese

systems(50%dilutedμE,5g/L,scheduleA)arepresentedinTable2.1.Thepressuredrop

Page 42: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

34

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

5g/L2.5cmx15cmcolumn

5g/L1cmx15cmcolumn

calculatedfromEquation9was22”water,lowerthanthereportedvalueof38”inTable2.1,

howeveritistobeexpectedgivenotherpressurelossesintheentireconfiguration.

Figure2.8Breakthroughcurvesof5g/L(asFe2O3)μEsuspensionofironoxideinjectedat

5m/day(porevelocity)throughcolumnswithaspectratioof15(left)and6(right).Thesolid

linesshowthesolutionofthe3-compartmentmodelusingtheconstantssummarized.

AsshowninFigure2.8,whenthesameexperimentwasconductedintwodifferentcolumn,the

outcomewasverysimilar.Whilebothcolumnstudiesappeartodisplayasecondarypeakatthe

end,thisfeaturecouldonlybereproducedasatailingeffectthroughthereversibleadsorption

compartment.Thistailingeffectissimilartootherreportedstudies[6][22][24]anditisbelieved

tobeduetoreversibledeposition.Table2.1showsthatthefittingparametersusedforboth

modelswerethesamewiththeexceptionofaslightlyhigherkrevforthecolumnwithaspect

ratioof6.Thehighercoefficientofdetermination(R2)obtainedwiththe2.5cmx15cmcolumn

Page 43: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

35

(aspectratio6)wasmainlyduetothelargernumberofsamplespointsthatonecancollectfor

thatsystem.

Becauseofthelargernumberofsamplingpoints,andthemorehomogeneousflowwithinthe

column,the2.5cmx15cmcolumn(aspectratio6)wasusedfortherestofthestudies.

ForthesebaselinesystemsofFigure2.8,theattachmentefficiency(α)wasoftheorderof10-3,

whichisinlinewiththelowerrangereportedbyKocuretal.forlowporevelocities[12].

However,whencomparingthesystemswiththeclosestcharacteristics(2.5g/LNZVI,v=4

m/day),theirattachmentefficiency(α)wascloseto0.2,almosttwoorderofmagnitudehigher

thanthesystemsexploredinFigure2.1.Thissuggestthatatleastfortheconditionsofthe

curvesinFigure2.8,theuseofμEassuspendingmediaimprovestheabilitytotransportthe

particles.AnotherinterestingobservationintheworkofKocuretal[19],andtheworkof

Tufenkjietal.[37]isthattheoptimalsizetominimizethesinglecollectorefficiency(ηo)isclose

to500nm,whichisthefinalsizeoftheaggregatesintheeffluentofthecolumn.Thedrawback

ofusinglargerparticlesizeisthattheycansinkundertheeffectofgravityandaccumulateat

thebottomofthecolumn(ortheaquifer).Thesettlingvelocity(vgr)ofsphericalparticlesin

dilutesuspensions,inlaminarflowcanbeestimatedusingtheStokesequation:

𝑣f0 =(ghAgi)∙f∙XYZ+

Bcd (10)

whereρpisthedensityoftheironoxideparticle(5200kg/m3)andρfisthedensityofthefluid

(assumedwater,1000kg/m3).Consideringaparticleof270nmina250cPfluid,thesettling

velocityfromEquation10is5.8E-5m/d,wellbelowtheporevelocityusedinthiswork.Particle

aggregatesinbetween100nmand1000nmaretoobigtodiffuseviarandommotion,butat

thesametime,toosmalltosettle,thusthesuitabilityofparticlesinthisrangetofacilitatethe

Page 44: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

36

transportoftheparticles.Theintrinsicdiffusivity(Dint)ofthe270nmparticlesina250cPfluid

canbeestimatedusingtheStokes-Einsteinequation:

𝐷?j# =kl∙m

UndXYZ (11)

wherekBisBoltzmann’sconstantandTisthetemperatureofthesystem(298K).Atthese

conditionstheintrinsicdiffusivityoftheparticlesis6.5·10-11cm2/s.Thisvalueissubstantially

smallerthanthevalueoftheorder10-5to10-6cm2/sfortheeffectivediffusivityofparticlesin

Table2.1.Potentialback-mixing(non-idealplugflow)mayberesponsibleforthelarger

effectivediffusivity.Infact,thelaminarnatureoftheflowcreatesadispersioneffectasthe

particlestravellingclosertothesurfaceoftheporeswillhavealowervelocitythantheparticles

travellingalongthecenterofthepore.Theeffectivediffusion(Deff),ordispersion,coefficient

(duetolaminarflowsegregation)canbeestimatedusingTaylor’sdispersionequation:

𝐷1oo =2∙pYZ+

+

qcrHs; (11)

For270nmparticles,injectedat5m/day,withDint=6.5·10-11cm2/s,Deff=2·10-6cm2/s,a

valuethatisclosertotheeffectivediffusioncoefficientfoundinTable2.1.

AlthoughtheresultsaboveshowthatthetransportofparticlesisfavouredinthediluteμE

systems,thereisapracticalissueinvolvedwithusingtheconditioning/rinsingprescribedin

scheduleA(Figure2).ScheduleAprescribesinjecting10PVofa10%NaClsolutionbeforeand

aftertheinjectionofthemicroemulsion.Thishighconcentrationofsaltcanimpactthe

chemistryandecosystemoftheaquifer.Tothisend,itwouldbebesttoinjectalowionic

strengthsolutionthatwouldbemorecompatiblewithexistinggroundwater.However,thisis

likelytohaveanimpactonthephasebehavioroftheμEironoxidesuspension.Toassessthis

Page 45: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

37

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

ScheduleB

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

ScheduleA

potentialimpact,abreakthroughcurvewasobtainedusingscheduleB(deionizedwater

conditioning/rinsing).ThecomparisonbetweentheseschedulesispresentedinFigure2.9.

AsshowninFigure2.9,theintroductionofdeionizedwater,insteadof10%NaCl,producesa

significantreductionontherecoveryofironoxidenanoparticles,fromvaluescloseto90%

(scheduleA)tocloseto60%(scheduleB).ForScheduleB,theattachmentefficiency(α)

increaseto0.023thatis,still,oneorderofmagnitudelowerthanthatofKocuretal.[19].

Figure2.9Breakthroughcurvesobtainedfor5g/LμEironoxideinjectedat5m/day(pore

velocity)througha2.5cmx15cmcolumn(aspectratioof6),usingscheduleA(10%NaCl

conditioning/rinsingfluid)andscheduleB(deionizedwaterconditioning/rinsingfluid.

TheresultsofFigure2.9confirmthehypothesisthatchangesinsalinitymayinducephase

changesthatdestabilizetheparticles.Togainabetterunderstandingofthetransportofthe

Page 46: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

38

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

ScheduleA ScheduleB

microemulsionitself,theexperimentsofFigure2.9wererepeated,butintheabsenceofiron

oxidenanoparticles.Figure2.10presentsthebreakthroughcurvesfordilutedμEsinjectedusing

schedulesAandB.

Figure2.10BreakthroughcurvesobtainedfordilutedμEs(noironoxide)injectedat5m/day

(porevelocity)througha2.5cmx15cmcolumn(aspectratioof6),usingscheduleA(10%NaCl

conditioning/rinsingfluid)andscheduleB(deionizedwaterconditioning/rinse).

Whentheparametersofthe3-compartmentmodel(Table2.1)fortheparticle-freedilutedμEs

(Figure2.10)arecomparedtothosecontaining5g/Lironoxide(Figure2.9)onefindsthatthey

arealmostthesame,withtheexceptionthatthevolumeratioofthereversiblecompartmentis

larger(frev)whichresultsinamorepronouncedtailingeffect.Furthermore,theattachment

constant(Katt)iszerofortheparticle-freeμEinjectedwithscheduleAanditissmallforthe

Page 47: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

39

particle-freeμEinjectedwithscheduleB.Evenintheabsenceofironoxideparticles,thelarge

changesinsaltconcentrationexperiencedduringscheduleBinduceirreversiblelosesofμEto

thecolumn.

Despitethelowerrecovery,scheduleBisstillmorefavourableforpotentialapplicationas

deliverystrategyduetothelowerriskofimpactingthechemistryandecosystemofthe

reservoir.Also,undesirabledensenon-aqueousphaseliquid(DNAPL)mobilizationcouldalso

occurifthesystemiskeptatconditionsthatcanproduceultralowinterfacialtensions,asisthe

caseforscheduleA[10][16].

AfinalpointofinterestregardingthepotentialuseofμE–basedsuspensionsistheestimated

traveldistance(Lmax),accordingtoEquation7.EvenwhenusingScheduleB,themaximum

penetrationdistanceisintheorderofhundredsofmeters.Thisdistanceissubstantiallylarger

thanthetypicalwelltowelldistanceinNZVIremediation,andlargerthanthosereportedfrom

otherstudies(intherangeof1-10meters)[44].

μE,% 100 100 50 50 50 50 50Fe2O3,g/L 10 10 5 5 5 0 0vpore,m/day 5 20 5 5 5 5 5Aspectratio 15 15 15 6 6 6 6Schedule A A A A B A BDeff·10-5,cm2/s - - 8.7 8.7 0.87 8.7 8.7krev·10-6,1/s - - 5.8 7.7 7.7 7.7 7.7frev - - 0.1 0.1 0 0.2 0.2Katt·10-6,1/s - - 0.31 0.31 1.4 0 0.19Recovery,% 0 58 88 88 56 100 93Cmax/Co - - 0.9 0.9 0.7 0.94 0.91α·10-3 - - 5.4 5.4 23.9 ND NDLmax,m - - 863 863 197 ND 1382R2fit 0.8 0.92 0.98 0.94 0.92ΔPmax,“H2O >100 >100 >100 38 35 36 35

Page 48: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

40

Table2.1Summaryofbreakthroughcurveparameters

2.3.5IronDistributionAnalysis

Figure2.11comparesthedistributionofironoxidedepositedonthecolumnbetweenthe

transportofthe5g/LironoxidenanoparticlesfollowingschedulesAandB.Forthecaseof

scheduleA,becauseofthehighrecovery,theamountofretainedironperweightofthesandis

low.Thepredictedattachediron(fromthe3-compartmentmodel)matchesthemeasurediron

attachedtosand.ToputthenumbersofFigure2.11inperspective,Xinetal.[24],injected5PV

of3g/L(Fe)NZVIat8.3m/day(conditionssomewhatsimilartoourstudy),obtainingan

attachedironof5mg/g,morethanoneorderofmagnitudelargerthantheironattached

obtainedinFigure2.11.

ComparedtoscheduleA,moreironwasattachedinscheduleB.The3-compartmentmodel

predictioncoincideswiththeretentioninthebottomofthecolumnoperatedwithscheduleB,

butnotintherestofthecolumn,wheretheamountofironattachedwaslowerthanthe

predictedamount.ThiscouldsuggestthatnotalltheattachmentinthecaseofscheduleBwas

attachmenttothesand,butapartitiontogel-likestructuresthatwerenotcollectedwhenthe

sandwassampledfromthecolumn.

ThepicturesforthescheduleAstudyshowbarelyvisiblespecksonthesurfaceoftheparticles

homogenouslydistributedthroughoutthegrains.ForthecaseofscheduleB,largerspecksare

shown,likelytheresultofaggregation,especiallyatthebottomofthecolumn.

Page 49: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

41

Figure2.11Ironoxidedepositedonsandcolumnaftertheinjectionof1.5PVof5g/L(as

Fe2O3)ironoxidenanoparticlesat5m/day(porevelocity)througha2.5cmx15cmcolumn

(aspectratioof6),usingscheduleA(10%NaClconditioning/rinsingfluid)andscheduleB

(deionizedwaterconditioning/rinsingfluid).Thesolidlinerepresentsthepredictionof

depositedironfromthe3-compartmentmodel.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 3 6 9 12 15

Attached

iron

oxide

,mgF

e/gs

and

Columnlength,cm

ExperimentalPredicted

1mm

ScheduleA

ScheduleB

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 3 6 9 12 15

Attached

iron

oxide

,mgF

e/gs

and

Columnlength,cm

ExperimentalPredicted

1mm

Page 50: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

42

2.4Conclusions

Theoriginalintentofthisworkwastoevaluatethetransportofmicroemulsion(μE)stabilized

ironnanoparticlesthroughporousmedia,usingironoxidenanoparticlesasmodelsystem.The

original10g/L(asFe2O3)suspensiondespitebeinghighlystable,ithadrheologicalproperties

thatpreventeditsuseatporevelocitiesconsistentwiththoseusedinaquiferremediation.

Dilutingthemicroemulsiontoa5g/Lsuspensionachievedreasonablepressuredropsatpore

velocitiesof5m/day,consistentwiththoseusedinaquiferremediation.

Thecolumnstudiesconsideredinthisworkwereanalyzedusinga3-compartmenttransport

modelthataccountforthetransportinthecolumnandtheexchangeofparticleswitha

reversibleadsorptioncompartmentandanirreversibleattachmentcompartment.

TheμEusedtosuspendthenanoparticleswaspreviouslydesignedtoformbicontinuous

systemsthatupondilutionin10%NaClbrinesolutionwouldyieldworm-likemicelles.When

usinga10%NaClbrinesolutiontoconditionandrinsethecolumnaftertheinjectionofthe

suspension,alargefractionofnanoparticleswasrecoveryandtheparticleattachment

experiencedinthecolumnwaslessthan1/10theattachmentobtainedwithothersuspension

mediareportedintheliterature.Whendeionizedwaterwasusedasconditioning/rinsing

solutionmoreparticleswereretainedbythecolumn,likelybecausephasetransitions

experiencedbytheμEphaseduetothelargechangeinelectrolyteconcentration.However,

eventhislessdesirabletransportwasstillmoreefficientthanothersuspensionsreportedinthe

literature.FuturestudiesshouldconcentrateinproducingμEsuspensionswithlowelectrolyte

concentrationsuchthatthecolumncanbeconditionedandrinsedwithlowenoughionic

strengthsolutionsthatwouldnotinducesubstantialchangesintheμEphasebehavior.

Page 51: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

43

2.5References:[1] F.Fu,D.D.Dionysiou,andH.Liu,“Theuseofzero-valentironforgroundwaterremediationandwastewater

treatment:Areview,”J.Hazard.Mater.,vol.267,pp.194–205,2014.

[2] C.M.Kocur,A.I.Chowdhury,N.Sakulchaicharoen,H.K.Boparai,K.P.Weber,P.Sharma,M.M.Krol,L.Austrins,C.

Peace,B.E.Sleep,andD.M.O’Carroll,“CharacterizationofnZVImobilityinafieldscaletest,”Environ.Sci.Technol.,

vol.48,no.5,pp.2862–2869,2014.

[3] P.G.TratnyekandR.L.Johnson,“Nanotechnologiesforenvironmentalcleanup,”NanoToday,vol.1,no.2,pp.44–48,

2006.

[4] B.Sunkara,J.Zhan,J.He,G.L.McPherson,G.Piringer,andV.T.John,“Nanoscalezerovalentironsupportedon

uniformcarbonmicrospheresfortheinsituremediationofchlorinatedhydrocarbons,”ACSAppl.Mater.Interfaces,

vol.2,no.10,pp.2854–2862,2010.

[5] A.B.Cundy,L.Hopkinson,andR.L.D.Whitby,“Useofiron-basedtechnologiesincontaminatedlandandgroundwater

remediation:Areview,”Sci.TotalEnviron.,vol.400,no.1–3,pp.42–51,2008.

[6] Y.H.Lin,H.H.Tseng,M.Y.Wey,andM.DerLin,“Characteristicsoftwotypesofstabilizednanozero-valentironand

transportinporousmedia,”Sci.TotalEnviron.,vol.408,no.10,pp.2260–2267,2010.

[7] J.Quinn,C.Geiger,C.Clausen,K.Brooks,C.Coon,S.O’Hara,T.Krug,D.Major,W.S.Yoon,A.Gavaskar,andT.

Holdsworth,“FielddemonstrationofDNAPLdehalogenationusingemulsifiedzero-valentiron,”Environ.Sci.Technol.,

vol.39,no.5,pp.1309–1318,2005.

[8] N.C.Mueller,J.Braun,J.Bruns,M.Černík,P.Rissing,D.Rickerby,andB.Nowack,“Applicationofnanoscalezerovalent

iron(NZVI)forgroundwaterremediationinEurope,”Environ.Sci.Pollut.Res.,vol.19,no.2,pp.550–558,2012.

[9] J.E.Huff,“ApplicationofEmulsifiedZero-ValentIron:FourFull-ScaleRemediationSites,”Remediat.J.,pp.125–136,

2011.

[10] S.Bettina,W.Hydutsky,andL.Bl,“DeliveryVehiclesforZerovalentMetalNanoparticlesinSoila

ndGroundwater,”vol.21,pp.2187–2193,2004.

[11] C.Mystrioti,N.Papassiopi,A.Xenidis,D.Dermatas,andM.Chrysochoou,“Columnstudyfortheevaluationofthe

transportpropertiesofpolyphenol-coatednanoiron,”J.Hazard.Mater.,vol.281,pp.64–69,2015.

[12] J.Zhan,T.Zheng,G.Piringer,C.Day,G.L.Mcpherson,Y.Lu,K.Papadopoulos,andV.T.John,“Transportcharacteristics

ofnanoscalefunctionalzerovalentiron/silicacompositesforinsituremediationoftrichloroethylene,”Environ.Sci.

Technol.,vol.42,no.23,pp.8871–8876,2008.

[13] T.Phenrat,N.Saleh,K.Sirk,R.D.Tilton,andG.V.Lowry,“Aggregationandsedimentationofaqueousnanoscale

Page 52: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

44

zerovalentirondispersions,”Environ.Sci.Technol.,vol.41,no.1,pp.284–290,2007.

[14] A.TiraferriandR.Sethi,“Enhancedtransportofzerovalentironnanoparticlesinsaturatedporousmediabyguargum,”

J.NanoparticleRes.,vol.11,no.3,pp.635–645,2009.

[15] J.Chen,Z.Xiu,G.V.Lowry,andP.J.J.Alvarez,“Effectofnaturalorganicmatterontoxicityandreactivityofnano-scale

zero-valentiron,”WaterRes.,vol.45,no.5,pp.1995–2001,2011.

[16] Z.WangandE.Acosta,“FormulationdesignfortargetdeliveryofironnanoparticlestoTCEzones,”J.Contam.Hydrol.,

vol.155,pp.9–19,2013.

[17] P.Jiemvarangkul,W.X.Zhang,andH.L.Lien,“Enhancedtransportofpolyelectrolytestabilizednanoscalezero-valent

iron(nZVI)inporousmedia,”Chem.Eng.J.,vol.170,no.2–3,pp.482–491,2011.

[18] D.O’Carroll,B.Sleep,M.Krol,H.Boparai,andC.Kocur,“Nanoscalezerovalentironandbimetallicparticlesfor

contaminatedsiteremediation,”Adv.WaterResour.,vol.51,pp.104–122,2013.

[19] C.M.Kocur,D.M.O’Carroll,andB.E.Sleep,“ImpactofnZVIstabilityonmobilityinporousmedia,”J.Contam.Hydrol.,

vol.145,pp.17–25,2013.

[20] T.Phenrat,Y.Liu,R.D.Tilton,andG.V.Lowry,“AdsorbedpolyelectrolytecoatingsdecreaseFeonanoparticle

reactivitywithTCEinwater:Conceptualmodelandmechanisms,”Environ.Sci.Technol.,vol.43,no.5,pp.1507–1514,

2009.

[21] N.Saleh,K.Sirk,Y.Liu,T.Phenrat,B.Dufour,K.Matyjaszewski,R.D.Tilton,andG.V.Lowry,“SurfaceModifications

EnhanceNanoironTransportandNAPLTargetinginSaturatedPorousMedia,”Environ.Eng.Sci.,vol.24,no.1,pp.45–

57,2007.

[22] S.M.HosseiniandT.Tosco,“Transportandretentionofhighconcentratednano-Fe/Cuparticlesthroughhighlyflow-

ratedpackedsandcolumn,”WaterRes.,vol.47,no.1,pp.326–338,2013.

[23] E.DVecchia,MLuna,andR.Sethi,“Transportinporousmediaofhighlyconcentratedironmicro-andnanoparticlesin

thepresenceofxanthangum,”Environ.Sci.Technol.,vol.43,no.23,pp.8942–8947,2009.

[24] J.Xin,F.Tang,X.Zheng,H.Shao,andO.Kolditz,“Transportandretentionofxanthangum-stabilizedmicroscalezero-

valentironparticlesinsaturatedporousmedia,”WaterRes.,vol.88,pp.199–206,2016.

[25] S.Laumann,V.Micić,andT.Hofmann,“Mobilityenhancementofnanoscalezero-valentironincarbonateporous

mediathroughco-injectionofpolyelectrolytes,”WaterRes.,vol.50,pp.70–79,2014.

[26] N.D.BergeandC.A.Ramsburg,“Oil-in-wateremulsionsforencapsulateddeliveryofreactiveironparticles,”Environ.

Sci.Technol.,vol.43,no.13,pp.5060–5066,2009.

Page 53: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

45

[27] A.I.A.Chowdhury,M.M.Krol,C.M.Kocur,H.K.Boparai,K.P.Weber,B.E.Sleep,andD.M.O’Carroll,“NZVIinjection

intovariablysaturatedsoils:Fieldandmodelingstudy,”J.Contam.Hydrol.,vol.183,pp.16–28,2015.

[28] P.Bennett,F.He,D.Zhao,B.Aiken,andL.Feldman,“Insitutestingofmetallicironnanoparticlemobilityandreactivity

inashallowgranularaquifer,”J.Contam.Hydrol.,vol.116,no.1–4,pp.34–46,2010.

[29] Z.Wang,“SYNTHESISOFSTABLEANDREACTIVEMICROEMULSIFIEDZERO-VALENTIRONNANOPARTICLES(MENZVI)

USINGEXTENDEDSURFACTANT,”2015.

[30] E.A.FrancisChoi,“MechanismofStabilityofParticleSuspensionsviaLipophilicMicellesby,”2015.

[31] V.Dwarakanath,K.Kostarelos,G.A.Pope,D.Shotts,andW.H.Wade,“Anionicsurfactantremediationofsoilcolumns

contaminatedbynonaqueousphaseliquids,”J.Contam.Hydrol.,vol.38,no.4,pp.465–488,1999.

[32] D.A.Sabatini,R.C.Knox,J.H.Harwell,andB.Wu,“IntegrateddesignofsurfactantenhancedDNAPLremediation:

Efficientsupersolubilizationandgradientsystems,”J.Contam.Hydrol.,vol.45,no.1–2,pp.99–121,2000.

[33] Z.Wang,A.Lam,andE.Acosta,“SuspensionsofIronOxideNanoparticlesStabilizedbyAnionicSurfactants,”J.

SurfactantsDeterg.,vol.16,no.3,pp.397–407,2013.

[34] E.M.Hotze,T.Phenrat,andG.VLowry,“Nanoparticleaggregation:challengestounderstandingtransportand

reactivityintheenvironment.,”J.Environ.Qual.,vol.39,pp.1909–1924,2010.

[35] R.A.CraneandT.B.Scott,“Nanoscalezero-valentiron:Futureprospectsforanemergingwatertreatment

technology,”J.Hazard.Mater.,vol.211–212,pp.112–125,2012.

[36] K.Yao,M.T.Habibian,andC.R.O’Melia,“WaterandWasteWaterFiltration:ConceptsandApplications,”Environ.Sci.

Technol.,vol.5,no.11,pp.1105–1112,1971.

[37] N.TufenkjiandM.Elimelech,“CorrelationEquationforPredictingSingle-CollectorEfficiencyinPhysicochemical

FiltrationinSaturatedPorousMedia,”Environ.Sci.Technol.,vol.38,no.2,pp.529–536,2004.

[38] R.Nowakowski,“Computersimulationofnon-linearpreparativechromatographyprocesses,”Chromatographia,vol.

28,no.5–6,pp.293–299,1989.

[39] K.J.Ward,S.C.Kaliaguine,P.A.Tanguy,andG.Jean,“Numericalsimulationofachromatographcolumn:linearcase,”

Ind.Eng.Chem.Res.,vol.27,no.8,pp.1474–1480,1988.

[40] S.Lakshmanan,W.M.Holmes,W.T.Sloan,andV.R.Phoenix,“Nanoparticletransportinsaturatedporousmedium

usingmagneticresonanceimaging,”Chem.Eng.J.,vol.266,pp.156–172,2015.

[41] J.Li,S.Bhattacharjee,andS.Ghoshal,“Theeffectsofviscosityofcarboxymethylcelluloseonaggregationandtransport

ofnanoscalezerovalentiron,”ColloidsandSurfacesA:PhysicochemicalandEngineeringAspects,vol.481.pp.451–

Page 54: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

46

459,2015.

[42] A.MandalandA.Bera,“Modelingofflowofoil-in-wateremulsionsthroughporousmedia,”Pet.Sci.,vol.12,no.2,pp.

273–281,2015.

[43] D.Thies-WeesieandA.Philipse,“Liquidpermeationofbidispersecolloidalhard-spherepackingsandtheKozeny-

Carmanscalingrelation,”Journalofcolloidandinterfacescience,vol.162,no.2.pp.470–480,1994.

[44] F.He,M.Zhang,T.Qian,andD.Zhao,“Transportofcarboxymethylcellulosestabilizedironnanoparticlesinporous

media:Columnexperimentsandmodeling,”J.ColloidInterfaceSci.,vol.334,no.1,pp.96–102,2009.

Page 55: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

47

Chapter3:Developmentandtransportofphosphatesurfactant,SDEHP-

stabilizedNZVIinporousmediaforinsituremediation

3.0Abstract

Nanoscalezero-valentiron(NZVI)particleshasbeenidentifiedasefficientreducingagentsfora

widerangeofgroundwatercontaminants;however,itsapplicationislimitedbythepoor

transportanddeliveryintheporousmedia.Inthiswork,sodiumDiEthylHexylPhosphate

(SDEHP)surfactantwasusedasasurfacemodifiertoimprovethemobilityofNZVIinsoil.An

optimalSDEHP-stabilizedNZVIformulation,100mMSDEHP1g/LNZVI,wasidentifiedthrough

criticalmicelleanalysisandtotalorganiccarbonanalysis.Simple“one-pot”NZVIsynthesis

procedurewasadaptedandmodifiedtosynthesizeNZVIformulations.TheSDEHPsurface

modifierimprovedthestabilityofbareNZVIfromminutestomonths.Theoptimized

formulationyieldedahydrodynamicdiameterabout240nmunderdynamiclightscattering

(DLS)and100nmindiameterundertransmissionelectronmicroscope(TEM).Acolumnstudy

ofthestableformulationisconductedwitha2.5x15cmglasscolumnfilledwithOttawasand

atafieldscaleflowvelocityof1.5m/daywithnomechanicalstirring.Theresultofthecolumn

studyshowedthatover95%ofNZVIarerecoveredwithasteadyplateauC/Copeakreachingto

1.AdiscussionsuggestedthatthedevelopedSDEHPsurfacemodifierholdsdesirabletraitsfor

afieldscaleinsituremediation.

Page 56: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

48

3.1Introduction

Nanoscalezero-valentiron(NZVI)particlesarerecognizedasanusefulgroundwater

remediationtechnologybecauseofitshighefficiencyinreducingawiderangeofcontaminants,

includingbutnotlimitedtoDNAPLandheavymetals[1][2][3][4].However,thistechnologyis

limitedbythepoormobilityinsoil[5][6].TheunmodifiedNZVIparticles,commonlyknownas

bareNZVI,duetohighmagneticandVanderWaalforces[3][7],aggregateandsettlewithin

minutesofbeingsynthesized.AggregatedZVIdemonstratedlosesitsoriginalhighsurfacearea

andbecomelessreactivetotargetcontaminants.TheseLargerparticlesarefilteredbythesand

grain,hinderingtheZVIparticlesfromreachingthecontaminantzoneandimmobilizedinsoil

[8].

TransportofNZVIinporousmediaisinfluencedbyvariousfactorssuchastransportvelocity,

pH,particlesizes,ionicstrength,soilmatrixandthecompositionofgroundwater[9][10].NZVI

particlestendtoaggregateandsettlebeforeencounteringthesoilmatrixandgroundwateror

clogattheearlystageofsubsurface[11][12].Addressingthestabilityissuebyeliminatingor

extendingthesettlingtimeandkeepingtheoriginalsizesoftheparticleshasbeenshownto

improvenanoparticlesmobility[13][14].Fortunately,particlesizesandstabilityofthe

suspensionarealsocloselyrelatedandcaneasilybeengineeredthroughtheapplicationof

surfacestabilizers[15][16][11][17],namelysurfacestabilizers.Currently,extensiveresearch

effortshavebeencommittedtotheapplicationofsurfacestabilizersonNZVI,includingto

polymers,surfactantsandemulsionsareused[13][18][15].However,surfacestabilizationon

NZVIparticlescanreducethereactivityofthereactiveparticlesbycreatingabarrierbetween

contaminantsandNZVI[19];alongwithothertrade-offssuchasconcentration[20][13][21]and

Page 57: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

49

injectiontechnique[8][22],stabilizedNZVIarenotalwayscandidatesforfieldremediation.

O’Carrolletal.summarizedthreefundamentalcharacteristicsthatanefficientlystabilizedNZVI

shouldhold:1.Demonstrateprolongparticlestability2.SufficientNZVIconcentration(1-12

g/L)toachievesuccessfulremediationand3.Maintainanadequatereactively[3].Applying

surfacestabilizersthatprovidethethreefundamentalcharacteristicshasbeentheobjectiveof

thisandotherstudies.

Laboratorycolumnexperimentsareoftenthefirststeptodetermineandassesstheabilityofa

stabilizedNZVI.Table3.1summarizes,theperformanceofselectednanoparticlesstabilizers

andtheircolumntransportresults[6][13][23][18][22][24][25][26][27][28][29].Outofthese

stabilizers,carboxyl-methylcelluloseNZVIat1g/LwasfieldtestedinSarnia,ONin2014by

Kocuretal.[30]Overall,thesurfacestabilizerscanimprovethestabilityandthusthemobilityof

theironnanoparticlesuspensionwithgreaterrecoveryandtransportchrematistics;however,

furtherimprovementsarehinted.7outofthe10listedcolumnstudieslistedwereconducted

ataflowvelocitybetween7.8to198.7m/day,wellabovethetypicalgroundwaterflowvelocity

of0.25to0.4m/day[3],implyingacompatibilityissueduringtheprocessofinjection[31].

Additionally,adequatebreakthroughperformanceofNZVIareonlyobservedatthelow

concentrations(below1g/L)forcarboxyl-methylcellulose,guargumandpoly(acrylicacid)

basedNZVI[29][8][16];whilealltheNZVIstabilizersincludingsurfactantTween-80yielded

poorbreakthroughresultsathigherconcentrationswithlowmaximumpeakanduneven

breakthroughcurves.Thismeansthatmoresevereagglomerationandinstabilityareobserved

athigherconcentrations[7].Furthermore,polymerstabilizerssuchascarboxyl-methylcellulose

althoughclaimedaprolongedstabilizationof80-hours,aggregationswerenotfullyeliminated

Page 58: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

50

andsettlingisobservedconstantlyoverthe80-hourperiod.Intheaforementionedfieldstudy

ofcarboxyl-methylcelluloseNZVI,itwasreportedthatNZVIcantravelatleast1meterwitha

recoveryrateof1%[30][32].ItisclaimedbySoukupovaetal.thatevena10dayperiodof

negligibleaggregationisnotenoughforafullscaleremediation[27].Non-ionicsurfactant

stabilizedNZVI,Tween-80,demonstrateda2-monthstabilityunderstoragecondition;however,

instabilitywasobserveduponcontactingwiththeporousmedia.Ontheotherhand,emulsion

encapsulatedNZVI,eventhoughyieldedahighandsteadyrecoverypeak(Cmax/Co)ata

desirablefieldflowvelocity(0.4m/day);theinjectionofemulsionNZVIrequiresconstantly

mechanicalstirringandcreateddifficultyininjection.Althoughapplyingsurfacestabilizers

improvedthemobilityofNZVIinporousmedia,laboratorycolumnstudiesshowedthatthere

hasn’tbeenasurfacestabilizerstrongenoughforanefficientfull-scaleremediation.Other

words,asurfacestabilizerthatcansatisfythebasicNZVIcharacteristicswithnoaggregation

andsettlingovertimehasyetbeenfound.

Surfactantsaresometimespreferredoverpolymersasstabilizingagentsbecausetheyhavea

highertendencytoadsorbontothesurfaceofnanoparticles[27].Biodegradablenon-ionic

surfactantssuchasTween-20,Tween-80andAlkylethanolamidesareoftenadaptedas

alternativestabilizersforNZVIforenvironmentalreasonsandsmoothsynthesis[33][34][27].It

isalsoreportedthatsurfactantscanincreasethereductionrateofthecontaminantsdueto

synergisms[35][36].Eventhoughnon-ionicsurfactantsholdseveraladvantages,theystill

producepoorstability[12].Wangetal.showedthatanionicsurfactantscanformelectrostatic

repulsionsbetweencoatedparticlesandsand,creatinganenergybarrierforNZVI

agglomeration[15].Itisalsoproventhatanionicsurfactantironnanoparticleswithstrong

Page 59: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

51

chargedcoatingsholdmoderatestabilityandmobility,assummarizedinTable1,namelyoleate

ionstabilizedironoxidenanoparticles[23].

Figure3.1StructureofanionicphosphatesurfactantSDEHP.

Inthisstudy,sodiumdiethylhexylphosphate(SDEHP),ananionicsurfactanthasbeenselected

asthestabilizerbecauseofitsnon-toxic,mildnatures[37].AndthefactthatWangetal.

demonstratedthatsodiumdodecylphosphate(SDP),anotherphosphatebasedsurfactant,can

actasastabilizerandpromotethereductionofchlorinatedhydrocarbons[38].Figure3.1

showsthestructureofsurfactantSDEHP,withphosphategroupbeingthehydrophilicheadand

doublecarbonchains.ItwasreportedthatSDP,anotherphosphatesurfactant,doesnotreact

withNZVIasastabilizerbutinfactpromotethedechlornatingreactions.Inadditional,itis

importanttonotethatphosphonategroupinanionicsurfactantsplayamajorroleinforming

morestablesuspensionwithmetalnanoparticles[39].Withthisknowledge,surfactantswith

phosphategroup[39]thatsharesimilarpropertiesareexpectedtohavesimilarperformancein

suspension.TheSDEHPanionicsurfactant,withthereactivityadvantageoverthetypical

biodegradablenon-ionicsurfactants,wasselectedasapotentialstabilizerofNZVIfor

developinganefficientalternativeforNZVIinsituremediation.

Page 60: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

52

Table3.1Literaturesummaryofcolumnstudiesandstabilitybehaviourfordifferenttypesof

surfacemodifiedironoxideandZVInanoparticles.

TheprimaryobjectiveofthispaperistodevelopaSDEHPsurfactant-basedformulationthat

SystemNo.

Max.Conc.(g/L)

Stability TransportVelocity(m/Day)

Viscosity Cmax/Co Size(nm)

Reference

Carboxyl-methylCelluloseNZVI

1 0.1-2.5 80hourswithaggregation

0.25,2,4 13.8-72.8

0.85-0.75(Decreasingtrend)

25-61 [13]

Polyeletrolyte-stabilizedNZVI

2 0.085-1.7

Stirringwhileinjection

6.4 0.97 0.8 85(particle)185(hydrodynamic)

[40]

EmulsionNZVI 3 2.5 Kineticallystable~8hours/Mixingduringinjection

0.4 9300 0.8-1 1000(droplet)12(particles)

[41]

PolyacrylicAcid-StabilizedNZVI

4 0.1,0.3,4

3hoursAgitationrequired

6.28-15.67 N/A ~1 ~100nm [6]

Polyphenol-basedNZVI

5 1 >10days 7.4 N/A 0.5 n/a [28]

GuarGumNZVI

6 0.154 Days 2.38-11.92 0.89-1.35

0.21(lowflow)-0.87(highflow)

320 [20]

XantumGumNZVI

7 3 72hours 8.4-198.72 ShearThinning10,000

0.4-0.6(increasingtrend,lowflow)0.8-1(fastestflow)

microscale [26]

Tween80NZVI

8 20%(w/w)0.32(columnstudy)

2monthsunderstorageconditions

24.32 N/A N/A 40-80 [27]

Oleate(OL)ionsstabilizedironoxide

9 5 >2weeks 14 N/A 0.93 N/A [23]

MicroemulsionIronoxide

10 5and10 >6months 5,20 20-400 0.9 120 Chapter2

Page 61: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

53

demonstratesprolongedstabilityandminimumaggregationusingtheframeworkproposedby

Wangetal.[15].Thesecondaryobjectiveistoexamineandassessthemobilityinporousmedia

oftheoptimalSDEHP-basedNZVIviaa1Dcolumnstudy.

3.2Methodology

Unlessotherwiseindicated,alltheproceduresandmaterialswerepreparedandconductedat

standardambienttemperatureandpressure(SATP).

3.2.1SynthesisofSodiumDiEthylHexylPhosphate(SDEHP)Surfactant

TheprocedureofproducingSDEHPwasadaptedfromthepublicationsofLuanetal.withsome

modification[37].Inshort,30,50and100mMofSDEHPwassynthesizedviatheneutralization

reactionbetweensodiumhydroxideandhydrogendiethylhexylphosphateacid(HDEHPA,

Sigma-Aldrich,237825,97%).3gofHDEHPAismeasuredbyweightusinganelectronicbalance

(Sartorius,Germany,33904396)ina20mLvialtomake100mMofSDEHP.Themeasured

HDEHPAisthentransferredtoa100mLvolumetricflaskwiththeflushingofDIwater.1M

Sodiumhydroxide(NaOH,Caledon,lot#89075)solutionwasaddedtothevolumetricflaskat

1.2timesthestoichiometricamount.BalancetherestofthevolumetricflaskwithDIwaterand

inducevigorousmixingmanually.Afterthesolutionturnedclear,stoppedthemixingandplace

thevolumetricflaskfor24hourstoreachcompleteequilibrium.Thecompletionofthe

neutralizedSDEHPsolutionwasthenconfirmedwithapHprobe(Vernier,Model:LD2-LE)to

determinetheacidity.Itisrecommendedtoaddseveraldropsofthe1MNaOHsolutionifthe

pHoftheSDEHPsolutionisbelowpH9,thehigherpHenvironmentguranteefullconversionof

theHDEHP.

Page 62: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

54

3.2.2CriticalMicelleConcentrationofSDEHPwithdissolvediron

SurfacetensionmeasurementsusingKSVSigmaTensiometer(model700)wasusedto

determinethecriticalmicelleconcentration(CMC)forSDEHP.Ironsulfate(FeSO4[H2O]7,Fisher

Scientific,7782-63-0)wasdissolvedintoSDEHPsurfactantsolutionatthefollowing

concentrations:10,25,30,50,80and100mM.Atotalof0.2gofironsulfate(equivalentto1

g/LNZVI)wasaddedto40mLofeachSDEHPsolutionatdifferentconcentrationwithgentle

mixing.Thesurfactant-ironsolutionwasthenmixedandplacefor1hourtoreachequilibrium

beforemeasurement.Thepurposeofdissolvingironsulfateistosimulatethesynthesis

condition.Identicalprocedurewasconductedforferricchloride(FeCl3,SigmaAldrich,7705-08-

0)andthoseresultsareshownanddiscussedinAppendixA.

3.2.3TotalOrganicCarbon(TOC)ofirondissolvedSDEHP

Totalorganiccarbon(TOC)analysiswasconductedusingatotalcarbonanalyzer(TOC-Vcpn,

SHIMADZU)fordeterminingtheamountofsurfactantadsorptiontotheiron.SDEHPsurfactant

solutionwaspreparedatthefollowingconcentrations:10,30,50,80and100mMfor10mLin

a20mLvial.DifferentconcentrationsofironsulfatesatdifferentNZVIequivalence

concentrationsrangesfrom0.3,0.5,1,1.5,2,2.5,3,4to5g/Lareadded.Thesampleswere

thencappedandmixedfor2minutesusingavortexmixerat1000rpm,thencentrifuged(Cole-

Parmer,1741423)at4000rpmfor45minutes.Thesupernatantwasdecantedandfilteredwith

anano-filter(PallCorp.AcrodiscSyringeFilter,450nm).Thefilteredsolutionwasdilutedto12.5

timesbeforeanalysis.

3.2.4SynthesisofSDEHPNZVI

NZVIiscommonlysynthesizedfromthereductionreactionbetweensodiumborohydride

Page 63: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

55

(NaBH4)andiron[42][43][44][2].TherearetwocommonNZVIsynthesismethods,namely

chloride-basedandsulfate-basedsynthesis[43].Inthiswork,sulfate-basedmethodisselected

forreasonsthatwillbefurtherexplainedinresultanddiscussion.ThereactionofNZVIsulfate-

synthesisisasthefollowing:

2𝐹𝑒Ww +𝐵𝐻qA + 3𝐻W𝑂 → 2𝐹𝑒a + 𝐻W𝐵𝑂UA + 4𝐻w + 2𝐻W (1)

The“one-pot”synthesisprocedurewasadaptedfromtheoriginalsynthesisprocedure

describedbyWangetal.forsynthesizingmicroemulsionNZVI[45].Specifically,surfactant

solutionsatthedesiredconcentrations(30,50and100mM)werepreparedusingdeaeratedDI

water.Thesurfactantsolutionsandotherreactantswereplacedinanitrogenfilledgloveboxfor

threehourstoremoveadditionaloxygen.Afterthethreehours,20mLofthesurfactant

solutionwastransferredtoa250mLbeaker.Toproducea1g/Lironsolution,0.1gofiron

sulfatewasweightedusinganelectronicbalanceinsidethegloveboxandtransferredtothe250

mLbeaker.Usingaglassstirringrod,manualgentleagitationwasusedtodissolvetheiron

sulfateforabout15minutes.Atotalof0.04gwasofsodiumborohydride(NaBH4,Sigma-

Aldrich,16940-66-2)wasweightedintheglovebox.Thesodiumborohydridewasslowlyadded

intothesolutionwithin30minutestopreventexcessivegasevolutionfromthereaction.After

this,thesolutionwasleftfor1hourinthegloveboxtoletthesolutiontocooldowntoroom

temperature.Thereductionyielded20mLof1g/LNZVIat30,50or100mMofSDEHP

surfactant.Similarprocedureswereusedtoproduce0.3,0.5,2and5g/LNZVI.Figure3.2

illustratedthedescribedone-potsynthesisprocessofNZVI.

Page 64: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

56

Figure3.2Illustrationofthe“one-pot”synthesisprocedureofSDEHP-stabilizedNZVI.The

procedurewasconductedintheglovebox.

3.2.5pHAnalysis

ApHmeterprobewasusedtoanalyzethepHofSDEHPsurfactantat100mMandSDEHP

stabilizedNZVIatdifferentironconcentrationsandsurfactantconcentrations2monthupon

synthesis.

3.2.6StabilityAnalysis

Uponsynthesis,SDEHPNZVIatdifferentformulationsandbareNZVIaretakenoutsideofthe

glovebox(synthesiscondition)forfurthercharacterization.Toassesscolloidalstability,the

synthesizedformulationswerere-suspendedwithasonicationbathfor1minute.Pictureswere

takenattimeintervalof15,30,60,120and180minutesforthefirstthreehoursanddailyfor

oneweekafterre-suspension.

Page 65: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

57

3.2.7ViscosityAnalysis

Tomeasuretheviscosityofthesynthesizedsolutions,syringeaspirationtimemethodwasused

[46].ThreeSDEHPNZVIformulations,SDEHPat100mMandDIwateraremeasured.Thewater

viscositymeasurementwasusedasthereferencepointtodeterminetheviscosityofthe

formulations.

3.2.8SizeAnalysis

Dynamiclightscattering(DLS)andtransmissionelectronmicroscope(TEM)areusedtoanalyze

thehydrodynamicandparticlesizesofthesynthesizedSDEHPNZVI,respectively.ForDLS

analysis,thefreshlysynthesizedNZVIatdifferentconditionswerediluted10timeswithDI

waterina20mLvialinthesynthesisconditionwithagloveboxfilledwithmixedair(95%N2

andbalanceCO2).PriortoDLSanalysis,thesamplewasmixedwithavortexmixerfor30

secondsandsonicatedusingasonicationbath(Cole-Parmer,8891)for1minute.Thesample

wasthenanalyzedviaaDLSparticlesizeanalyzer(BrooklynInstrumentCrop,90Plus)

measurementsfor10minutes.ForTEManalysis,identicalproceduretoDLSanalysiswas

followedforsamplepreparationpriortoanalysis.ATEMmicroscope(Hitachi,HF3300)was

usedforanalyzingtheironparticlesizes.

3.2.8ColumnExperimentProcedure

Aglasscolumn(15x2.5cm,KontesBrand,ChromaFlex,No.420830-1S1D)wasfilledwithacid-

washedOttawasand(Silicondioxide,Sigma-Aldrich,60676-86-0)asporousmediumfor1-D

transportanalysis.Thesandmediumwaswet-packedandstirredduringpackingtoremoveair

trappedinthesand.Thecolumnwasweightedbeforeandafterpackingandmassbalancewas

performedtodeterminetheporevolume(1porevolumeorPV=32mL).Aperistaticpump

Page 66: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

58

(Cole-Parmer,MasterFlexL/S)wasusedforthisexperimentandtheflowratewassatatthe

lowestsettingat0.5mL/min(equivalentto1.5m/dayasflowvelocity).Thepumpisconnected

toathree-way-valvetoallowswitchingbetweentheflushingfluidandthenanoparticle

solutions.TominimizeNZVIoxidiation,anenclosurewasinstalledaroundtheSDEHPNZVI

solutiontoeliminateoxygenfromtheambient.Inspecific,aN2gascylinderwasconnectedto

anexpandablesmallgloveboxwithapurgestreamataconstantrateof20psi.Thecontinuous

purgingofthenitrogensimulatesthesynthesizingconditionintheglovebox.Theexperiment

startswiththeflushingstage,aninjectionof10porevolumes(320mL)offlushingfluid(DI

water)fromthebottomofthecolumn.Uponcompletionoftheflushingstage,2porevolumes

(64mL)of100mMSDEHPNZVIsolutionwasinjectedintheidenticalcondition.The

transportedsolutionwascollectedwithanautomaticfractionalcollectoratarateof1.5

mL/sample(3minutes)startingfromtheNZVIinjectionstage,thesamplingiscontinueduntil

theendoftheexperiment.Another10porevolumesofDIwaterwereinjectedtothecolumn

towashouttheNZVI.Thecollectedsamplesfromthecollectorismixedwith6Nhydrochloric

acid(HCl,BDH,BDH7204-1)atvolumeratioof1:4(Nanoparticlessolution:HCl6N)for

concentrationandbreakthroughcurveanalysis.Theoverallexperimentalschematicwas

illustratedinFigure3.3.

Page 67: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

59

Figure3.3ColumnstudysetupforSDEHP-stabilizedNZVI.

3.2.9NZVIColumnDistributionAnalysis

Uponcompletionofthecolumnstudy,thesandwasrecoveredfromthecolumntodetermine

thedistributionoftheironretainedinthecolumn.Thecolumnwasdividedintofivesections,

witheachonesectionbeing3cminlength.Thecolumnwasdisconnectedandaspatulawas

usedtoretrievedfromeachsection.Theretrievedsandwasanalyzedunderamicroscopefor

particleadsorptionandunderUV/VISspectroscopyforconcentration.Priortothe

concentrationanalysis,thesandwasdigestedinHCl6Nfor3dayswasingasand-acidratioof1

g/5mL.

3.3ResultsandDiscussion

3.3.1DeterminingtheOptimalSynthesisFormulation

Aframeworktodeterminingtheoptimalsurfactant-nanoparticlesformulationisvitalfora

stablesuspension.Inthepast,severalstudieshaveattemptedtouseanionicandnon-ionic

surfactanttosuspendmetalnanoparticlesincludingNZVI[47][39][48][49][30].Ontheother

Page 68: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

60

hand,Wangetal.successfullyoptimizedwithaframeworkfortwoanionicsurfactantstabilized

ironnanoparticlestoyieldastablesuspensionforover24hours[23].Asimilarformulationfor

ironnanoparticlesathighconcentrationwasconcludedtobemobileinporousmediathrougha

columnstudybyWangetal[23].Tothisday,nostudyhasusedanyframeworkorstrategyto

determinethemostefficientsurfactantstabilizedNZVIformulation.

ThisstudyadaptedtheformulationstrategyproposedbyWangetal.thatastablenanoparticle

suspensioncanbeachievedifthesurfactantconcentrationisabovethecriticalmicelle

concentration(CMC)afterreachinganequilibriumwithnanoparticles[15].Thedetermination

oftheoptimalformulationofNZVIwasthusdividedintotwoparts:1.TodeterminetheCMCof

SDEHPwiththepresenceironsulfateand2.Todeterminethehighestironconcentration

possibleinthelowestSDEHPconcentrationsolutiontosynthesizeNZVI.

Figure3.4showsthesurfacetensionmeasurementsatdifferentconcentrationofSDEHPfrom

10to100mMwith1g/Lequivalenceofironsulfatedissolved.Theadditionofironsulfate

simulatesNZVIsynthesisconditionwiththesurfacemodifierpriortothereaction.Ferrous

sulfatemayaltertheoriginalCMCconsideringtheinteractionoftheferrousionwiththe

anionicsurfactantthatleadtotheformationofferroussalts,someofwhichprecipitatefrom

solutions.Figure3.4presentstwosurfacetensionmeasurementcurvesfortheaforementioned

scenario.Curve1fromFigure3.4representstheoriginalSDEHPconcentrationandcurve2

representsthecorrectedconcentrationofnon-adsorbedSDEHPbasedonTOCanalysis.From

curve1inFigure3.4,itcanbeobservedthatthesurfacetensiondecreasedlinearlyfrom45

mN/mto25mN/matconcentrations10,20,30and50mMofSDEHP.From50mMonwardsto

100mM,thesurfacetensionreachedtoaplateauatapproximately25mN/m.Thegeneral

Page 69: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

61

trendimpliedinfigure3.4isatypicalsurfacetensioncurveofasurfactantandisconsistent

withotherreportedCMCmeasurementsbytheSDEHPstudyinliterature[37][50].Through

logarithminterpolationbetweenthedescendingandplateausectionofthesurfacetension

curve,itwasdeterminedthattheCMCofSDEHPwith1g/LequivalenceNZVIofironsulfate

dissolvedisabout57mM.Thisisabout30-40mMhigherthanthevaluesreportedbyother

studieswithpureSDEHPsurfactant[37][50][51].ThedramaticraiseintheCMCimpliesthatthe

presenceofironsulfatedidhaveanimpactonthebehaviourofthesurfactantlikelyduetothe

precipitationofferroussaltsofDEHP.Inotherwords,thedissolvedironfromtheironsulfate

areactingasadditionalsurfacesforthesurfactantmolecules.Ontheotherhand,theCMC

impliedincurve2isclosertothereportedliteraturevalue.Theadditionalsurfacesprovidedby

theironparticlesdelayedtheformationofemptymicellesandthusshouldbetakenaccount

whenformulatingforthestabilizationofNZVIsuspension.Overall,theresultofCMCbasedon

thestrategyproposedbyWangetal.impliesthattheminimumSDEHPinitialsynthesis

concentrationshouldbewellabove57mMwiththesurfactantadsorptionbeingconsidered.

Page 70: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

62

Figure3.4Surfacetensionmeasurementsof1g/LofNZVIdissolved:Curve1showsthe

surfacetensionmeasurementoftheoriginalSDEHPconcentrationandCurve2displayedthe

correctedconcentrationofSDEHP.

ThesecondpartofdetermininganoptimalconditionforsuspendingNZVIistoidentifySDEHP

formulationsthatcanholdthehighestNZVIconcentration.Totalorganiccarbon(TOC)wasused

todeterminetheconcentrationofun-adsorbedSDEHPinthemixtureofironsulfateand

SDEHP.TOCcananalyzethedissolvedSDEHPinthesolutionconsideringthatthesurfactantis

theonlyorganicmaterialintheformulation.Figure3.5showstheequilibriumsurfactant

concentrationasafunctionoftheaddedSDEHPmixingwithironsulfateconcentrationsfor

variousaddedSDEHPconcentration(initial).30mMSDEHPwith1g/LFedissolvedfromferrous

sulfatewasusedasthe‘worstcasescenario’forstability/synthesiscomparison.100mMSDEHP

0

5

10

15

20

25

30

35

40

45

50

1 10 100

SurfaceTensionm

N/M)

SDEHPConc.(mM)

SurfaceTensionofSDEHPw/1g/LofFeSO4dissolved

Curve1:Original Curve2:"Corrected"

Page 71: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

63

isthehighestconcentrationtestedduetotheexponentialraiseinviscositybeyond100mM.As

expected,anegativecorrelationisobservedbetweenthefreesuspendingSDEHPconcentration

andtheamountofironsulfatedissolved.Inotherwords,thehigherconcentrationsofiron

sulfateparticlesprovidemoresurfacesforsurfactantmoleculestoadsorbon,thusgivingless

suspendingSDEHP.ConnectingbacktotheSDEHPCMCfindingsof41mMfromsurfacetension

measurement,stablesuspensionsareexpectedtobefoundatironsulfateconcertationfrom

0.3to1.5g/Lfor80and100mMSDEHPand0.3to1g/Lironsulfateconcentrationsfor50mM

SDEHP.ConsideringthattheamountoffreesuspendingSDEHPareenoughtoformempty

micellesandmeettheminimumstandardoftheframework.

Figure3.5DissolvedSDEHPequilibriumconcentrationwithironVS.addedironsulfate

concentrationsfordifferentinitialSDEHPconcentrations.

0

20

40

60

80

100

120

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

DISSOLVED

SDE

HPCONC.(M

M)

CONCENTRATIONOFFE2SO4

100mMSDEHP 80mMSDEHP 50mMSDEHP 30mMSDEHP

Page 72: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

64

3.3.2SynthesisResultsandStabilityofFeSO4-basedSDEHPNZVIat100mMand1g/L

Figure3.6TEMimagingof10mMSDEHP-stabilizedNZVIat1g/Lwithdifferentscaleat500

nmscale.

The100mMSDEHP-stabilizedNZVIat1g/LwasidentifiedasthemostsuccessfulNZVI

suspensionwithastabilityofover2months.Table2summarizedthelistofcandidatesthat

wereselectedforNZVIsynthesiswiththegoalofachievingprolongedcolloidalstability.Figure

3.6displaystheTEMimagingofthemostsuccessfulSDEHP-stabilizedNZVIformulationand

furtherdiscussedinsection3.3.4.

Page 73: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

65

a. b.

c. Figure3.7SetA,TimelapsephotosofSDEHP-stabilizedNZVIat0.5g/LofNZVIatvarious

SDEHPconcentrations:a.30mMofSDEHPb.50mMofSDEHPandc.100mMofSDEHP.

Figure3.7and3.8demonstratetwosetsofstabilitytimelapsephotos.Infigure3.7,thefirstset

(setA)ofphotos,30,50and100mMofSDEHPNZVIformulationsaredisplayedandmonitored

forstabilityover2days(48hours).Fromfigure3.7,ashypothesized,theNZVIparticles30mM

formulationwasquicklyaggregatedandformedsedimentationwithin30minutesuponre-

suspensionandsynthesis.The100mMNZVIformulation,withfreesuspendingSDEHP

concentrationofcloseto100mM,demonstratedprolongedstabilityinsuperiortotheother

twocandidates.Nosignsofsedimentationsandstable,evendistributionoftheparticleswere

observed48hoursafterre-suspension.Thesuspensionremainedstabletwomonthsafterre-

Page 74: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

66

suspensionandphaseseparationwasobservedduetooxidation.Thehighconcentrationsof

theSDEHPsurfactantalongwiththeadditionoftheNZVIparticlesformwormlikemicellesdue

tothelowpackingandthenatureoftheSDEHPsurfactant[52].Thewormlikemicellescan

anchorontothesurfaceofthenanoparticlesandprovideprolongedstability[53].Signsofthe

formationofwormlikemicellescanbeobservedthroughtheformationofliquidcrystal[54]in

the100mMSDEHPNZVIformulationandnotobservedin30and50mMincontrast(not

shown).Inaddition,anincreaseinviscosityisalsoasigninformationofthewormlikemicelle

asdemonstratedinTable2.Basedontheabove,100mMSDEHPNZVIformulationisselected

forfurtherconcentrationanalysisduetothesuperiorstabilityat0.5g/L.

a.

Page 75: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

67

b.

Figure3.8SetB,Stabilitytimelapsepictureof100mMatNZVIconcentration1,1.5and2g/L

overaperiodof24hours:a.1hourandb.24hoursaftersynthesisandre-suspension.

30mM0.5g/L

50mM0.5g/L

100mM0.5g/L

100mM1g/L

100mM2g/L

Stability <1hour ~1hour >2months >2months ~1hourHydrodynamicSize(nm)

482+/-150 792+/-89 287+/-26 244+/-30 412+/-22

Viscosity(cP) - - 1.4+/-0.03 1.4+/-0.03 1.2+/-0.09pH - - 8.8 9.3 7.8

Table3.2SynthesisresultandcharacterizationofSDEHP-stabilizedNZVIatvariousNZVIand

surfactantconcentrations.

Figure3.8showsthestabilityresultsof100mMNZVIat1,1.5and2g/L.Outofthethree,2g/L

showedaggregationandsedimentationupon1hourafterre-suspension,while1.5g/Llasted

justoveronehour.The1g/LofNZVIformulationdemonstratedidenticalstabilityasthe0.5g/L

100mMNZVIformulationdiscussedpreviously.Theresultsareconsistentwiththefactthat

increasingtheironsulfateconcentrationreducesdissolvedSDEHP(figure3.5),limitingitsability

toformtheworm-likemicellerequiredtostabilizetheparticles.

Page 76: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

68

InadditionaltotheironsulfatebasedNZVIsynthesis,ferricchloride-basedNZVIwasalso

attemptedfordeterminingastableNZVIstableformulation.Ferricchloride-basedNZVIat

identicalconditionsastheironsulfate-basedNZVIdidnotdemonstratethesamestability.

Rapidaggregationandsettlingwereobservedwithin45minutesto1houraftersynthesis.

DetailedresultsarepresentedanddiscussedinappendixA.

3.3.3pHandViscosityAnalysisandImplication

Viscosityismeasureduponsynthesistosomeoftheformulationsbasedontheirstability.

ViscosityofthestabilizedNZVIsuspensionneedstobemonitoredbecauseitcancritically

impactthemobilitywhenitistoolowortoohigh[41][16][55],asdiscussedinchapter2.The

viscosityofthesecondsetsofsynthesis,withdifferentNZVIconcentrationsalongwith0.5g/L

100mMSDEHPformulationfromthefirstsetweremeasured.TheoriginalSDEHP,without

additionofironsulfateandanysynthesisreactions,heldasimilarviscositytowaterat100mM,

approximately1cP.Uponsynthesis,theviscosityof1and0.5g/L100mMSDEHPNZVIshared

similarviscosity,approximately1.4cP.Thisisslightlyhigherthantheviscosityoftheoriginal

SDEHPsolutionby0.4cPat100mM.Theraiseinviscositycanbeexplainedbytworeasons:1.

Thecontributionoftheadditionofinorganicsolidnanoparticlesandcolloidtothesolution[53]

and2.Theformationofwormlikemicelle[56].Incontrast,the1.5g/Lalthoughdemonstrates

lowerstability,themeasurementswereconductedimmediatelyuponresuspensionbutwitha

lowerviscositymeasuredby0.2cP.Itisexpectedthattheincreaseofnanoparticleswill

increasetheviscosity;however,thisisnotthecasehere.Thisimpliesthattheformationof

wormlikemicellemaycontributetotheviscosityovertheadditionoftheparticles.Theviscosity

resultimpliesthepresenceofwormlikemicellesin0.5and1g/LSDEHP-stabilizedNZVIthat

Page 77: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

69

demonstratedhighstability.

ItisbelievedthatpHishighlycorrelatedwiththestabilityduetotheionicinteractionsbetween

thesurfacestabilizersandthehydrogenions[57].Usingzeta-potentialasanindicator,several

studiesreportedthatmodifiedmetalnanoparticlessuspensionexperiencedadecreasein

stabilityatpH6-7[12][23][55][43].Inotherwords,ahigherpHisexpectedforahighly

stabilizedsuspension.pHisalsoavariableoftencontrolledinotherstudiesanddeemedto

promoteimpactinreactivitywithlowerpHs[56][57].ThepHresultsaresummarizedinTable

2.Inthisstudy,0.5,1and2g/Lof100mMSDEHP-stabilizedNZVIformulationsaretestedfor

pH.Theoriginal100mMSDEHPsolutionisalsotested.FortheSDEHPonlypHmeasurement,

thepHisabout11implyingabasicenvironmentduetotheexcessNaOHusedinsynthesis.In

0.5and1g/Lsamples,thepHvariesbetween8.8-9.2,showingadecreasefromthepure

surfactant.Thisisbecausethesynthesisreaction,aslistedintheexperimentalsectionwill

produce2molesofhydrogenionsforeverymoleofNZVIproduced.Thehydrogenionsundergo

aneutralizationreactionwiththebasicsurfactantsolution,causingadropinthepH.Onthe

otherhand,2g/LsampleshowedalowerpHof7.8.Thisisconsistentwiththeotherdata,

consideringthathigherconcentrationofNZVIproducesmorehydrogenions,thusmore

neutralization.Theraiseinhydrogenionscanalsodisturbtheformationofwormlikemicelleor

theformationofemptymicellesingeneral,causinginstabilityofthesuspensionasobserved.

3.3.4SizeAnalysisofSDEHPNZVI

ControloftheparticlesizeduringsynthesisiscriticaltoasuccessfulNZVIsurfacestabilizer

[30][3],[14],[61],asmentionedinthethreestandards[3].Thestabilizersmodifiedorinduced

ontothesurfaceoftheNZVIwillincreasetheoverallparticlesizeandinfluencemobility.

Page 78: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

70

Specifically,higherparticlesizeswillincreasecontactwiththesandgrainandpromote

mechanismssuchasporestrainingandnegativelyimpactthemobility[40][20].Itwasreported

thatstrainingiscommonamongpolymer-stabilizedNZVIandmorelikelytooccurinfinerpore

sizeswithlargerparticlesizes[21][40].ItisimportantfortheSDEHPNZVItobeintheoptimal

transportsizebetween100-1000nm[61][62].Thecombinationofhydrodynamicandparticle

diametercanprovidethefullimageoftheparticlesizeofSDEHP-stabilizedNZVI[63].The

hydrodynamicdiameterprovidesthemeasurementofthefullparticlesizeofNZVIparticles

includingtheSDEHPanchoring.TheTEMimagesprovidemeasurementsoftheparticles

withoutthewormlikemicelleanchoring.Thehydrodynamicdiameterof0.5,1and2g/LSDEHP-

stabilizedNZVIaresummarizedinTable2.Thehydrodynamicsizesareabout278and244nm

for0.5and1g/L100mMSDEHP-stabilizedNZVI,respectively.Asignificantincreasein

hydrodynamicsizewasobservedat2g/L,holdinganaverageof412nmindiameter.Thesizeof

thenanoparticleisbelievedtoreflectthestabilityofthesuspension.Specifically,athigher

concentrations,inthiscase,2g/L,thelackofthepresenceofwormlikemicellecontributesto

therapidaggregationofthenanoparticles,causingtheaveragediametertobemorethan1.7

timeshigherthanthestableNZVIsuspensions.Conveniently,thehydrodynamicdiameterof

thestableSDEHP-NZVIsuspensionfellintotheoptimalsizeoftransport[61].TEMimagingof

theparticleforthemoststableformulation,1g/L100mMSDEHPisshowninFigure3.6.The

picturedemonstratedthattheNZVIparticleswithoutthesurfactantcoatingisabout100nm,

meetingthesizestandardproposedintheliterature.Surprisingly,net-likecoatingsare

observedintheTEMimagingaroundtheNZVInanoparticles.Thecoatingisbelievedtobethe

surfactantcoatingofthenanoparticlesisalsoobservedaroundthenanoparticles,givinga

Page 79: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

71

largerdiameterofapproximately300nm,whichisconsistenttothehydrodynamicdiameter.

Overall,theparticlesizeofthe1g/LSDEHP-stabilizedNZVIhighlystableformulation

demonstratedsuitablesizebythestandards.

3.3.5MobilityofSDEHPNZVIat100mMand1g/L

Figure3.9showsthebreakthroughcurveof1g/Liron,100mMSDEHP-stabilizedNZVI

transportingatthefieldflowrateof5m/daywithfittingfromthemodeldescribedinchapter2.

Thefittedmodelincludedthedispersionmechanismbutnoparticleattachmentmechanism.In

otherwords,particleattachmentsarenotapplicableinthetransportofSDEHP-stabilizedNZVI

duetothegoodtransport,thisisthefirstsignofgoodtransport.Theperformanceofthe

breakthroughcurveisanindicationontheperformanceofthemobilityofthesynthesized

NZVI-suspension.TwofeaturesonthebreakthroughcurveshowthatthehighstabilitySDEHP-

stabilizedNZVIholdsanexcellentmobility:1.Highrecoveryand2.Highandsteadyplateau

concentrationpeak.TherecoveryiscalculatedthroughtheratiooftheinjectedNZVIpore

volumeandtherecoveredporevolumeasthefollowing:

~8Hs�4�;4p~834��5434p

(2)

Therecoveryiscalculatedtobeashighas95%.Thehighrecoveryisbetterthanthevalue

reportedbyLinetal.,achievingarecoveryofalmost90%atahigherflowvelocityof15.87

m/day[29].ComparingtotheemulsionNZVIresult,therecoveryisinthesamerangeas

SDEHP-stabilizedNZVIandtheflowvelocityisconductedatlowervelocityof0.4m/day[22];

however,mechanicalstirringisintegratedfortheemulsifiedNZVI.Theresultsarecomparable

Page 80: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

72

tothepolyelectrolyte-stabilizedNZVIreportedbyRaychoudhuryetal.atacomparableflow

rateof6.4m/day[40].However,SDEHP-stabilizedNZVIachievedthehighrecoveryandplateau

valuesathigherironconcentrationswithoutconstantmxingduringinjection.SDEHP-stabilized

NZVIcouldachieveahighrecoveryatafieldflowratewhilenomechanicalstirringisneeded,

thisexcellentperformancewasneverreportedbyotherNZVIsuspension.Thehighandsteady

plateaurecovery(C/Co)isascloseas1,thisismuchbetterthanotherstudiesaswell.

Specifically,carboxyl-methylcelluloseNZVItransportstudyconductedbyKocuretal.achieved

asteadyplateauconcentrationat0.8and0.9C/Co,at0.1and2.5g/LNZVIconcentration,

respectively[13]at4m/day.Comparingtothisstudy,SDEHP-stabilizedNZVIachievedaslightly

higherC/CoatalowerNZVIconcentrationof1g/Latacomparableof1.5m/day.Thealmost

perfectplateauconcentrationalsoimpliedthatminimumretentionoccurredbetweenthesand

andtheNZVIparticles.TheminorresidualoftheNZVIinthecolumnisfoundonlyinthebottom

ofcolumnfromtheextractedsand,believedtobecausedbygravitationalsedimentationthat

wasobservedseverelyinotherstudies[64][28].Itcanbeconcludedbasedontheabovetwo

featuresthat,thedevelopedSDEHP-stabilizedNZVIcansuccessfullytransportthroughporous

mediawithoutdifficulty.

Page 81: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

73

Figure3.9ColumnstudybreakthroughcurveofhighlystableSDEHP-stabilizedNZVI,at100

mMSDEHPand1g/LofNZVIat5m/daywiththemodeldescribedinchapter2(solidline).

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 1 2 3 4

C/Co

Porevolume

Page 82: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

74

3.3.6NZVIColumnDistributionAnalysis

Figure3.1NZVIdistributionincolumngraphfor100mMSDEHP1g/LNZVIwithmicroscope

imagingat3,9and15cmsectionofthecolumn.

Figure3.10illustratesthedistributionofNZVIparticlesuponcompletionofalltheinjectionand

flushingintheexperimentalphase.Althoughthebreakthroughcurvefromfigure3.9implieda

highNZVIrecovery,tracesofNZVIretentionswereshownfromthedistributioncurveandthe

sandgrainmicroscopeimaging.Overall,theNZVIshowedadecreasingretentiontrendfromthe

bottomtothetopofthecolumn.Thetrendofthecolumndistributionprofileisconsistentwith

thefindingsreportedbyXinetal.[26].Itisimportanttonotethatdespitethesimilarityinthe

overallNZVIdistributiontrend,theamountofironretainedinthesandreportedinthisstudy

wasmagnitudesloweroftheresultbyXinetal.atsimilarconcentrationsandamuchlower

Page 83: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

75

flowvelocity[26].Comparingtotheirondistributioninchapter2,theresultsindicatedisabout

1timeslower,althoughconductedattheconcentrationinthisstudyis5timesless.Inother

words,figure3.10confirmsthecompellingtransportabilityofSDEHP-stabilizedNZVIinporous

media.Inadditional,visuallynolargeparticleswerefoundaroundtheporeinthesandanalysis,

concludingstrainingwastheleastlikelyretentionmechanism.

Comparingamongthethreemicroscopepicturesalongthecolumn,sometraceofNZVIwas

remainedonsandbutonlyatthebottomsectionofthecolumn(3cm).Thisisconsistentwith

thefindingsoftheretentionprofilethathighestNZVIwasfoundinthebottom.However,the

amountoftheNZVIremainedatthebottomofthesandwasconsideredminimalincomparison

tothefindingsinchapter2,thetransportofmicroemulsionironoxide.Thiscouldbe

interpretedasasignofgoodtransport,becausetherewasnegligibleformationofNZVI

blockageamongthesandgraininthecolumn.ItisbelievedthatthestrainedNZVIparticles

wereonlythelargerparticleswhensynthesized.Inshort,itcanbeconcludedbasedonthe

sandgrainimagingthatSDEHP-stabilizedNZVIsuspensiondidnotaggregateandsettlewhen

contactwiththesand.

3.3.7ImplicationsforinsituRemediation

Theultimategoalofthisstudyistodevelopasurfacestabilizerforafull-scaleremediation.

Basedonthefunctionalityandpropertiesofthestabilizationmethod,SDEHP-stabilizedNZVIis

expectedtobethebestcandidateoutofallthesurfacestabilizationtechniquesthusfar.In

termsoffunctionality,SDEHP-stabilizedNZVIsuspensioncanbeinjectedataflowvelocity

similartotheremediationvelocitywithoutanymechanicalstirring.TheSDEHP-stabilizedNZVI

holdsahighstabilitywithnosedimentationobservedforovertwomonths,thisgreatly

Page 84: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

76

improvesthechanceforasuccessfulinsituremediation.InthelatestfieldstudiesofCarboxyl-

methylcellulose-stabilizedNZVI,itisreportedthatnodirecttraceofNZVIwasfoundin

downstream,implyingagainthetransportissue.SDEHP-stabilizedNZVIdemonstratedideal

transportin1-DcolumnstudywithresultsthatweresuperiorcomparewithotherNZVI

suspensions.Inadditionaltothefunctionality,thepropertiesoftheappliedsynthesismethod

arealsoinfavourofafull-scaleremediation.ItiswidelyacceptedthatonsiteNZVIsynthesis

yieldsbetterremediationresultsincomparisontopre-synthesizedNZVI[3][30][62].One-pot

synthesisNZVItechniqueprovidesasimpleprocedureofsynthesizingSDEHP-stabilizedNZVI

consideringitssimplemethod.Lastly,surfactantSDEHPisachemicalthatiswidelyusedinthe

miningindustrywithnohistoryofenvironmentalconcerns[51].Thephosphategroupcanbe

naturallydegradeduponcontactwithsoil.Theamountofsurfactantusedintheformulation,

100mM,isabout3.5wt%andconsideredalowconcentrationcomparingtoemulsionNZVI,

thusnosideeffectonthetoxicity,whichisconcernofinsituNZVIremediation[65].Itis

concludedthatSDEHPisagoodtransportvehicleforNZVI,morestudiesinvolvingreactivityis

requiredandeventuallyapilot-scaleinsituremediationisneeded.

3.4Conclusion

ThisworksuccessfullydevelopedaSDEHP-NZVIformulationusingtheconceptproposedby

Wangetal.ThroughthedeterminationofCMC,therangeofthemoststableformulationis

narroweddown.TheTOCresultsfurtherprovidedarangeofiron-surfactantratioforsynthesis.

Thesynthesisandstabilityresultssuggestedthatthehighstabilitycanbeachievedbywormlike

micellesanchoringontheNZVIparticlesurfaceswhenthedissolvedSDEHPconcentrationis

closeto100mM.Inthemobilitystudy,becauseofthehighstability,1g/Liron,100mMSDEHP-

Page 85: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

77

stabilizedNZVIyieldedremarkablemobilityintheporousmediaatafieldflowvelocityof1.5

m/day.ThehighNZVIrecoveryandasteadypeakofthebreakthroughcurveimplythatthe

nanoparticlesexperienceminimalfiltrationduringtransport.Itisimpliedthatthecompelling

mobilityinporousmediademonstratedbySDEHP-stabilizedNZVIcanleadtostudiesatthe

higherscale.

Page 86: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

78

3.6References:

[1] A.B.Cundy,L.Hopkinson,andR.L.D.Whitby,“Useofiron-basedtechnologiesincontaminatedlandandgroundwater

remediation:Areview,”Sci.TotalEnviron.,vol.400,no.1–3,pp.42–51,2008.

[2] A.CorreiadeVelosaandR.F.PupoNogueira,“2,4-Dichlorophenoxyaceticacid(2,4-D)degradationpromotedby

nanoparticulatezerovalentiron(nZVI)inaerobicsuspensions,”J.Environ.Manage.,vol.121,pp.72–79,2013.

[3] D.O’Carroll,B.Sleep,M.Krol,H.Boparai,andC.Kocur,“Nanoscalezerovalentironandbimetallicparticlesfor

contaminatedsiteremediation,”Adv.WaterResour.,vol.51,pp.104–122,2013.

[4] F.Fu,D.D.Dionysiou,andH.Liu,“Theuseofzero-valentironforgroundwaterremediationandwastewater

treatment:Areview,”J.Hazard.Mater.,vol.267,pp.194–205,2014.

[5] S.Bettina,W.Hydutsky,andL.Bl,“DeliveryVehiclesforZerovalentMetalNanoparticlesinSoila

ndGroundwater,”vol.21,pp.2187–2193,2004.

[6] T.Raychoudhury,G.Naja,andS.Ghoshal,“Assessmentoftransportoftwopolyelectrolyte-stabilizedzero-valentiron

nanoparticlesinporousmedia,”J.Contam.Hydrol.,vol.118,no.3–4,pp.143–151,2010.

[7] T.Phenrat,A.Cihan,H.-J.Kim,M.Mital,T.Illangasekare,andG.V.Lowry,“TransportandDepositionofPolymer-

ModifiedFe0Nanoparticlesin2-DHeterogeneousPorousMedia:EffectsofParticleConcentration,Fe0Content,and

Coatings,”Environ.Sci.Technol.,vol.44,no.23,pp.9086–9093,2010.

[8] P.Jiemvarangkul,W.X.Zhang,andH.L.Lien,“Enhancedtransportofpolyelectrolytestabilizednanoscalezero-valent

iron(nZVI)inporousmedia,”Chem.Eng.J.,vol.170,no.2–3,pp.482–491,2011.

[9] N.SalehandH.Kim,“IonicStrengthandCompositionAffecttheMobilityofinWater-SaturatedSandColumns,”pp.

3349–3355,2008.

[10] D.B.Nyer,Evank.Vance,“Nano-ScaleIronforDehalogenation.pdf,”Treat.Technol.,2001.

[11] T.Phenrat,N.Saleh,K.Sirk,H.J.Kim,R.D.Tilton,andG.V.Lowry,“Stabilizationofaqueousnanoscalezerovalentiron

dispersionsbyanionicpolyelectrolytes:Adsorbedanionicpolyelectrolytelayerpropertiesandtheireffecton

aggregationandsedimentation,”J.NanoparticleRes.,vol.10,no.5,pp.795–814,2008.

[12] N.Saleh,K.Sirk,Y.Liu,T.Phenrat,B.Dufour,K.Matyjaszewski,R.D.Tilton,andG.V.Lowry,“SurfaceModifications

EnhanceNanoironTransportandNAPLTargetinginSaturatedPorousMedia,”Environ.Eng.Sci.,vol.24,no.1,pp.45–

57,2007.

[13] C.M.Kocur,D.M.O’Carroll,andB.E.Sleep,“ImpactofnZVIstabilityonmobilityinporousmedia,”J.Contam.Hydrol.,

Page 87: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

79

vol.145,pp.17–25,2013.

[14] T.Phenrat,H.J.Kim,F.Fagerlund,T.Illangasekare,R.D.Tilton,andG.V.Lowry,“Particlesizedistribution,

concentration,andmagneticattractionaffecttransportofpolymer-modifiedFe0nanoparticlesinsandcolumns,”

Environ.Sci.Technol.,vol.43,no.13,pp.5079–5085,2009.

[15] Z.Wang,A.Lam,andE.Acosta,“SuspensionsofIronOxideNanoparticlesStabilizedbyAnionicSurfactants,”J.

SurfactantsDeterg.,vol.16,no.3,pp.397–407,2013.

[16] N.Sakulchaicharoen,D.M.O’Carroll,andJ.E.Herrera,“Enhancedstabilityanddechlorinationactivityofpre-synthesis

stabilizednanoscaleFePdparticles,”J.Contam.Hydrol.,vol.118,no.3–4,pp.117–127,2010.

[17] F.He,D.Zhao,J.Liu,andC.B.Roberts,“StabilizationofFe-Pdnanoparticleswithsodiumcarboxymethylcellulosefor

enhancedtransportanddechlorinationoftrichloroethyleneinsoilandgroundwater,”Ind.Eng.Chem.Res.,vol.46,no.

1,pp.29–34,2007.

[18] N.D.BergeandC.A.Ramsburg,“Oil-in-wateremulsionsforencapsulateddeliveryofreactiveironparticles,”Environ.

Sci.Technol.,vol.43,no.13,pp.5060–5066,2009.

[19] W.Wang,M.Zhou,Z.Jin,andT.Li,“Reactivitycharacteristicsofpoly(methylmethacrylate)coatednanoscaleiron

particlesfortrichloroethyleneremediation,”J.Hazard.Mater.,vol.173,no.1–3,pp.724–730,2010.

[20] A.TiraferriandR.Sethi,“Enhancedtransportofzerovalentironnanoparticlesinsaturatedporousmediabyguargum,”

J.NanoparticleRes.,vol.11,no.3,pp.635–645,2009.

[21] S.M.HosseiniandT.Tosco,“Transportandretentionofhighconcentratednano-Fe/Cuparticlesthroughhighlyflow-

ratedpackedsandcolumn,”WaterRes.,vol.47,no.1,pp.326–338,2013.

[22] S.O’Hara,T.Krug,J.Quinn,C.Clausen,andC.Geiger,“FieldandlaboratoryevaluationofthetreatmentofDNAPL

sourcezonesusingemulsifiedzero-valentiron,”Remediat.J.,vol.16,no.2,pp.35–56,2006.

[23] Z.WangandE.Acosta,“FormulationdesignfortargetdeliveryofironnanoparticlestoTCEzones,”J.Contam.Hydrol.,

vol.155,pp.9–19,2013.

[24] M.Basnet,C.DiTommaso,S.Ghoshal,andN.Tufenkji,“Reducedtransportpotentialofapalladium-dopedzerovalent

ironnanoparticleinawatersaturatedloamysand,”WaterRes.,vol.68,pp.354–363,2015.

[25] S.Laumann,V.Micić,andT.Hofmann,“Mobilityenhancementofnanoscalezero-valentironincarbonateporous

mediathroughco-injectionofpolyelectrolytes,”WaterRes.,vol.50,pp.70–79,2014.

[26] J.Xin,F.Tang,X.Zheng,H.Shao,andO.Kolditz,“Transportandretentionofxanthangum-stabilizedmicroscalezero-

Page 88: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

80

valentironparticlesinsaturatedporousmedia,”WaterRes.,vol.88,pp.199–206,2016.

[27] J.Soukupova,R.Zboril,I.Medrik,J.Filip,K.Safarova,R.Ledl,M.Mashlan,J.Nosek,andM.Cernik,“Highly

concentrated,reactiveandstabledispersionofzero-valentironnanoparticles:Directsurfaceandsiteapplication,”

Chem.Eng.J.,vol.262,pp.813–822,2015.

[28] C.Mystrioti,N.Papassiopi,A.Xenidis,D.Dermatas,andM.Chrysochoou,“Columnstudyfortheevaluationofthe

transportpropertiesofpolyphenol-coatednanoiron,”J.Hazard.Mater.,vol.281,pp.64–69,2015.

[29] Y.H.Lin,H.H.Tseng,M.Y.Wey,andM.DerLin,“Characteristicsoftwotypesofstabilizednanozero-valentironand

transportinporousmedia,”Sci.TotalEnviron.,vol.408,no.10,pp.2260–2267,2010.

[30] C.M.Kocur,A.I.Chowdhury,N.Sakulchaicharoen,H.K.Boparai,K.P.Weber,P.Sharma,M.M.Krol,L.Austrins,C.

Peace,B.E.Sleep,andD.M.O’Carroll,“CharacterizationofnZVImobilityinafieldscaletest,”Environ.Sci.Technol.,

vol.48,no.5,pp.2862–2869,2014.

[31] A.I.A.Chowdhury,M.M.Krol,C.M.Kocur,H.K.Boparai,K.P.Weber,B.E.Sleep,andD.M.O’Carroll,“NZVIinjection

intovariablysaturatedsoils:Fieldandmodelingstudy,”J.Contam.Hydrol.,vol.183,pp.16–28,2015.

[32] L.Chekli,B.Bayatsarmadi,R.Sekine,B.Sarkar,A.M.Shen,K.G.Scheckel,W.Skinner,R.Naidu,H.K.Shon,E.Lombi,

andE.Donner,“Analyticalcharacterisationofnanoscalezero-valentiron:Amethodologicalreview,”Anal.Chim.Acta,

vol.903,no.August,pp.13–35,2016.

[33] S.R.KanelandH.Choi,“Transportcharacteristicsofsurface-modifiednanoscalezero-valentironinporousmedia,”

WaterSci.Technol.,vol.55,no.1–2,pp.157–162,2007.

[34] Y.T.Wei,S.cheeWu,S.W.Yang,C.H.Che,H.L.Lien,andD.H.Huang,“Biodegradablesurfactantstabilizednanoscale

zero-valentironforinsitutreatmentofvinylchlorideand1,2-dichloroethane,”J.Hazard.Mater.,vol.211–212,pp.

373–380,2012.

[35] D.weiLiang,Y.hanYang,W.weiXu,S.kanPeng,S.fuLu,andY.Xiang,“Nonionicsurfactantgreatlyenhancesthe

reductivedebrominationofpolybrominateddiphenylethersbynanoscalezero-valentiron:Mechanismandkinetics,”J.

Hazard.Mater.,vol.278,pp.592–596,2014.

[36] G.D.Sayles,G.You,M.Wang,andM.J.Kupferle,“DDT,DDD,andDDEdechlorinationbyzero-valentiron,”Environ.

Sci.Technol.,vol.31,no.12,pp.3448–3454,1997.

[37] Y.Luan,G.Xu,S.Yuan,L.Xiao,andZ.Zhang,“Comparativestudiesofstructurallysimilarsurfactants:Sodiumbis(2-

ethylhexyl)phosphateandsodiumbis(2-ethylhexyl)sulfosuccinate,”Langmuir,vol.18,no.22,pp.8700–8705,2002.

Page 89: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

81

[38] E.Wang,Ziheng;Choi,FrancisandAcosta,“EffectofSurfactantsonZero-ValentIronNanoparticles(NZVI)Reactivity.”.

[39] Y.Sahoo,H.Pizem,T.Fried,D.Golodnitsky,L.Burstein,C.N.Sukenik,andG.Markovich,“Alkyl

phosphonate/phosphatecoatingonmagnetitenanoparticles:Acomparisonwithfattyacids,”Langmuir,vol.17,no.25,

pp.7907–7911,2001.

[40] T.Raychoudhury,N.Tufenkji,andS.Ghoshal,“Strainingofpolyelectrolyte-stabilizednanoscalezerovalentiron

particlesduringtransportthroughgranularporousmedia,”WaterRes.,vol.50,pp.80–89,2014.

[41] M.Arhuoma,M.Dong,D.Yang,andR.Idem,“Determinationofwater-in-oilemulsionviscosityinporousmedia,”Ind.

Eng.Chem.Res.,vol.48,no.15,pp.7092–7102,2009.

[42] H.H.Tseng,J.G.Su,andC.Liang,“Synthesisofgranularactivatedcarbon/zerovalentironcompositesfor

simultaneousadsorption/dechlorinationoftrichloroethylene,”J.Hazard.Mater.,vol.192,no.2,pp.500–506,2011.

[43] W.ZhangandD.W.Elliott,“Applicationsofironnanoparticlesforgroundwaterremediation,”Remediat.J.,vol.16,no.

2,pp.7–21,2006.

[44] M.Stefaniuk,P.Oleszczuk,andY.S.Ok,“Reviewonnanozerovalentiron(nZVI):Fromsynthesistoenvironmental

applications,”Chem.Eng.J.,vol.287,pp.618–632,2016.

[45] Z.Wang,“SYNTHESISOFSTABLEANDREACTIVEMICROEMULSIFIEDZERO-VALENTIRONNANOPARTICLES(MENZVI)

USINGEXTENDEDSURFACTANT,”2015.

[46] S.Quraishi,M.Bussmann,andE.Acosta,“CapillaryCurvesforEx-situWashingofOil-CoatedParticles,”J.Surfactants

Deterg.,vol.18,no.5,pp.811–823,2015.

[47] D.K.Kim,MariaMikhaylova,YuZhang,andandMamounMuhammed,“ProtectiveCoatingofSuperparamagneticIron

OxideNanoparticles,”Chem.Mater.,vol.15,no.8,pp.1617–1627,2003.

[48] L.Bronstein,X.Huang,J.Retrum,A.Schmucker,M.Pink,B.D.Stein,andB.Dragnea,“Influenceofironoleatecomplex

structureonironoxidenanoparticleformation,”Chem.Mater.,vol.19,no.15,pp.3624–3632,2007.

[49] Y.C.Lee,C.W.Kim,J.Y.Lee,H.J.Shin,andJ.W.Yang,“Characterizationofnanoscalezerovalentironmodifiedby

nonionicsurfactantfortrichloroethyleneremovalinthepresenceofhumicacid:Aresearchnote,”Desalin.Water

Treat.,vol.10,no.1–3,pp.33–38,2009.

[50] Y.Luan,G.Xu,S.Yuan,L.Xiao,andZ.Zhang,“InvestigationsonNaDEHPandAOT:Computersimulationandsurface

tensionmeasurements,”ColloidsSurfacesAPhysicochem.Eng.Asp.,vol.210,no.1,pp.61–68,2002.

[51] C.Akbay,N.Wilmot,R.A.Agbaria,andI.M.Warner,“Characterizationandapplicationofsodiumdi(2-ethylhexyl)

Page 90: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

82

sulfosuccinateandsodiumdi(2-ethylhexyl)phosphatesurfactantsaspseudostationaryphasesinmicellarelectrokinetic

chromatography,”J.Chromatogr.A,vol.1061,no.1,pp.105–111,2004.

[52] A.ShioiandM.Tanabe,“EffectsofOrganicSolventsontheAggregates’GeometryandWinsorII/IIITransitioninthe

SodiumBis(2-ethylhexyl)PhosphateSystemAkihisa,”J.Phys.Chem.,no.97,pp.8281–8288,1993.

[53] F.Nettesheim,M.W.Liberatore,T.K.Hodgdon,N.J.Wagner,E.W.Kaler,andM.Vethamuthu,“Influenceof

nanoparticleadditiononthepropertiesofwormlikemicellarsolutions,”Langmuir,vol.24,no.15,pp.7718–7726,

2008.

[54] X.Wang,D.S.Miller,E.Bukusoglu,J.J.DePablo,andN.L.Abbott,“Topologicaldefectsinliquidcrystalsastemplates

forMolecularSelf-Assembly,”Nat.Mater.,vol.15,no.September,pp.1–9,2015.

[55] M.M.Krol,A.J.Oleniuk,C.M.Kocur,B.E.Sleep,P.Bennett,Z.Xiong,andD.M.O’Carroll,“Afield-validatedmodelfor

insitutransportofpolymer-stabilizednZVIandimplicationsforsubsurfaceinjection,”Environ.Sci.Technol.,vol.47,no.

13,pp.7332–7340,2013.

[56] M.E.Helgeson,T.K.Hodgdon,E.W.Kaler,N.J.Wagner,M.Vethamuthu,andK.P.Ananthapadmanabhan,“Formation

andrheologyofviscoelastic‘doublenetworks’inwormlikemicelle-nanoparticlemixtures,”Langmuir,vol.26,no.11,

pp.8049–8060,2010.

[57] K.Moore,B.Forsberg,D.R.Baer,W.a.Arnold,andR.L.Penn,“Zero-ValentIron:ImpactofAnionsPresentduring

SynthesisonSubsequentNanoparticleReactivity,”J.Environ.Eng.,vol.137,no.10,pp.889–896,2011.

[58] R.a.French,A.R.Jacobson,B.Kim,S.L.Isley,R.L.E.E.Penn,andP.C.Baveye,“Influenceofionicstrength,pH,

andcationvalenceonaggregationkineticsoftitaniumdioxidenanoparticles,”Environ.Sci.Technol.,vol.43,no.5,pp.

1354–1359,2009.

[59] J.Chen,Z.Xiu,G.V.Lowry,andP.J.J.Alvarez,“Effectofnaturalorganicmatterontoxicityandreactivityofnano-scale

zero-valentiron,”WaterRes.,vol.45,no.5,pp.1995–2001,2011.

[60] T.Satapanajaru,P.Anurakpongsatorn,P.Pengthamkeerati,andH.Boparai,“Remediationofatrazine-contaminated

soilandwaterbynanozerovalentiron,”Water.Air.SoilPollut.,vol.192,no.1–4,pp.349–359,2008.

[61] J.Zhan,T.Zheng,G.Piringer,C.Day,G.L.Mcpherson,Y.Lu,K.Papadopoulos,andV.T.John,“Transportcharacteristics

ofnanoscalefunctionalzerovalentiron/silicacompositesforinsituremediationoftrichloroethylene,”Environ.Sci.

Technol.,vol.42,no.23,pp.8871–8876,2008.

[62] B.Sunkara,J.Zhan,J.He,G.L.McPherson,G.Piringer,andV.T.John,“Nanoscalezerovalentironsupportedon

Page 91: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

83

uniformcarbonmicrospheresfortheinsituremediationofchlorinatedhydrocarbons,”ACSAppl.Mater.Interfaces,

vol.2,no.10,pp.2854–2862,2010.

[63] T.Phenrat,N.Saleh,K.Sirk,R.D.Tilton,andG.V.Lowry,“Aggregationandsedimentationofaqueousnanoscale

zerovalentirondispersions,”Environ.Sci.Technol.,vol.41,no.1,pp.284–290,2007.

[64] E.DVecchia,MLuna,andR.Sethi,“Transportinporousmediaofhighlyconcentratedironmicro-andnanoparticlesin

thepresenceofxanthangum,”Environ.Sci.Technol.,vol.43,no.23,pp.8942–8947,2009.

[65] N.C.Mueller,J.Braun,J.Bruns,M.Černík,P.Rissing,D.Rickerby,andB.Nowack,“Applicationofnanoscalezerovalent

iron(NZVI)forgroundwaterremediationinEurope,”Environ.Sci.Pollut.Res.,vol.19,no.2,pp.550–558,2012.

Page 92: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

84

Chapter4:ConclusionandRecommendations

Stabilityiscommonlyconcludedtobepositivelycorrelatedwiththemobilityofnanoscalezero

valentiron(NZVI)particles[1][2].ImprovingthestabilityofbareNZVIsuspensionsusingsurface

stabilizerscanpromotethemobilityofNZVIintheaquiferandeventuallyasuccessful

remediation[3].Currently,varioussurfacemodifiedNZVIsuspensionshavebeendeveloped

andtestedinbenchscale[3][4]andindustrialscale[5][6][7];however,aggregationand

sedimentationsarestillobservedandnosuccessfultransportreported.Overall,thisstudy

concludedtwoalternativetransportvehiclestoimprovethemobilityandstabilityofNZVI.

AlthoughNZVIremediationapplicationshavebeenconductedthroughacademicfieldstudies,

theextentofNZVIapplicationincontaminatedlandsisstilllimited.Inspecific,NZVIinsitu

remediationduetomobility,isfavouredinsoilwithhigherhydraulicconductivity.Theresults

fromthisstudyimpliedtwoalternativeNZVItransportvehicleandpotentiallyimprovethe

extentofNZVIremediation.

Inchapter2,microemulsion-stabilizednanoparticlesaresuggestedtobeanalternative

transportvehicleforNZVIinsituremediationbyWangetal.[8].Toassesstheintrinsicmobility

andeffectivenessofmicroemulsion-stabilizedNZVIdevelopedbyWangetal.[8],ironoxide

nanoparticlesareusedasananalogytoeliminatetheoxidizingfactorofNZVI.Inthecolumn

experiment,microemulsion-stabilizedironoxidenanoparticlesatveryhighconcentrations(2.5,

5and10g/L)arecharacterizedintermsofviscosity,hydrodynamicsize,particlesizeand

stability.Itisfoundthatmicroemulsion-stabilizedironoxidenanoparticlesholdidentical

stabilityperiodwithmicroemulsion-stabilizedNZVIwithsizesinthesimilarrangeasconfirmed

Page 93: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

85

bythesizeanalysis.However,therheologyanalysisimpliedthathigherironoxide

concentrations,10g/Land7g/L,hadahighviscosityofover400CPanddemonstratednon-

Newtonian,shear-thinningbehaviour.However,theviscositydrasticallydecreasedat5g/Liron

oxideconcentrationto20CPandreturnedtoNewtonianbehaviour.Itwasfoundthatthehigh

viscosityat10g/Lcontributedtothepoortransportobservedatthefieldof5m/day.In

contrast,underthesamecondition,at5g/Lironoxideformulation,highrecoveryandhigh

plateaupeakwasobserved.Inaddition,bychangingthesalinityconditionofthesandinthe

columnbetweenDIwatersaturatedandbrinesaturated(10g/L)atthesameconcentrationas

theformulation,thetransportresultischanged.Byshiftingthesalinitytozero,theplateau

peakisdecreasedsharply,implyingthehighsaltsensitivityofthemicroemulsion-stabilizer.

Microemulsion-stabilizedironnanoparticlesalthoughdemonstratedpromisingtransportresults

duetothehighstability,furtherimprovementsarerequiredforreducingthesensitivityofsalt

andviscosity.Itisconcludedthatmicroemulsioncanholdupto5g/Lofironoxide

nanoparticleswhiledemonstratingadequatetransportbehaviour.Viscosityandsalinitywere

identifiedascriticalvariablesforimprovingthefeasibilityoflargerscaleremediationstudies.

BasedonthefindingsinChapter2,surfactantSDEHP-stabilizedNZVIisdevelopedbasedona

formulationdesignframeworksuggestedbyWangetal.Chapter3discussedthedevelopment

ofahighlystabilizedanionicsurfactantstabilized-NZVIandtheassessmentonthemobilityof

theNZVIformulation.Inthedevelopment,formulationdesignframeworkbyWangetal.is

appliedforthefirsttimeinsurfactant-stabilizedNZVI[9].Anionicsurfactant,SDEHPisselected

forNZVIstabilizationbasedonthepackingpropertiesandenvironmentalfriendliness.Through

determiningcriticalmicelleconcentration(CMC)andtheratiobetweenSDEHPandironsulfate,

Page 94: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

86

1g/LNZVIat100mMSDEHPisidentifiedasthemostoptimalformulationyieldingastabilityof

over2months.TheNZVIformulationischaracterizedwithsizeandviscosityanalysis;withthe

resultsshowingsignsofidealNZVI.Thecolumnstudyatfieldvelocityresultsdemonstrated

excellenttransportofSDEHP-stabilizedNZVIwithhighrecoveryandplateaupeaks.The

developedformulationwasevaluatedforfieldstudypotentialandhighlightedtobeastrong

candidateforremediationduetotheoverallpropertiesofSDEHP-stabilizedNZVI.

DespitethefindingsinChapter3impliedthattheSDEHP-stabilizedNZVIishighlyfeasiblefora

fullscaleremediationapplication,somefutureworkisrecommendedforfurtherunderstanding

andoptimizingtheformulation.Firstly,theunderstandingofthereactivityoftheSDEHP-

stabilizedNZVIisconsideredpreliminary.Itwasunderstoodfromthepreviousreactivitystudy

fromWangetal.thatsodiumdodecylphosphate(SDP)-stabilizedNZVIduetothephosphate

group(PO43-)holdskineticsratewithreactiveblack5(RB5)andcarbontetrachloride(CT)close

totherateofbareNZVI[10].Inotherwords,thephosphategroup,thatpresentsinSDEHPas

well,maypromotethereactivitywithotherchlorinatedsolvents,makingSDEHP-stabilizedNZVI

moreefficient.Withthisimplication,areactivitystudyandtargetdeliverystudyis

recommendedforfuturework.Secondly,thestabilizationmechanismandthebehaviourof

surfactantaggregationarenotyetwellunderstoodintheSDEHP-stabilizedNZVIformulation.

Eventhoughsignsshowingthattheformationofwormlikemicelleplayedanimportantrolein

stabilization,theexactmechanismonthenanoscaleisstillhypothesized.Theformationof

wormlikemicelleswasnotfoundintheidenticalNZVIformulationwhentheinitialironsource

isfromironchloride(FeCl3).AsdemonstratedinAppendixB,thestabilitybehaviourofFeCl3

basedNZVIformulationistotallydifferentthantheironsulfatebasedformulationdescribedin

Page 95: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

87

Chapter3.Finally,theconcentrationoftheSDEHP-stabilizedNZVI(1g/L)discussedinChapter3

despitesufficientintermsofremediation,couldnotbescaledupduetothelimitationofthe

formulation.Themicroemulsion-basedNZVIisanimprovementoftheformulationtestedin

Chapter2andabletoholdhigherNZVIconcentrations.However,furtherunderstandingin

termsoftransportandmobilizationwithDNAPLisrequired.

Despitethestrongmobilityinporousmediawasdemonstratedbymicroemulsion-stabilized

ironnanoparticlesandSDEHP-stabilizedNZVI,furtherimprovementsarerecommendedfor

bothstabilizers.Formicroemulsion-stabilizedironnanoparticles,thehighsalinityofthe

formulation(10g/100mL)mustbeaddressedtopreventsaltcontaminationtolandsbefore

applications.Thehighsaltconcentration,asdiscussedinchapter2,wasnecessarytoproducea

one-phasemicroemulsion,wherethehydrophilic-lipophilic-differenceiszero(HLD=0)withthe

extendedsurfactantused.Loweringthesaltconcentrationwiththeexgtendedsurfactantwill

shifttheHLDoftheformulationandthuslosingthestability.BasedontheHLDequation,

alternativesurfactantswithahighercharacteristiccurvature(Cc)canreducethesalinity.

Phosphatesurfactantfromchapter3,SDEHPmayreducethesalinityrequiredtobalancethe

HLD,aSDEHPmicroemulsionsystemcanbedevelopedfollowingtheprocedureofWantetal.

FortheSDEHP-stabilizedNZVIdevelopedinchapter3,eventhoughsuccessfultransportwas

observedat1g/LNZVIconcentrationandmettheminimumremediationcriteria,higherNZVI

concentrationsarepreferredformoreefficientremediation.However,basedontheresultsin

chapter3,1g/ListhemaximumNZVIconcentrationpossible,consideringanysurfactant

concentrationhigherthan100mMwasnotfeasible.Basedontheresultsinchapter2,

microemulsionsystemscanholdironoxidenanoparticlesupto10g/L.TheSDEHP

Page 96: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

88

microemulsionsystemcanachievehigherconcentrationsandcanbeexpectedwithvariationof

thesynthesisprocedure.

Thesignificanceofthisstudyliesinthefollowing:1.ThetransportstudyontheSDEHP-

stabilizedNZVIconfirmedanimprovementonthemobilitytoporousmedia.Currently,thefull-

scaleremediationresultsofpolymer-stabilizednZVIsuggestedthatlongerdistanceandhigher

recoveryarerequired.ItcanbeexpectedthatSDEHP-stabilizedNZVIyieldedalongertravel

distanceandhigherrecoveryinthefieldtestfromtheresultsinthisstudy.2.Themobilitystudy

ofmicroemulsion-stabilizedironnanoparticlessuggestedthatgreaterconcentrationsofNZVI

canbetransportedinaneffectivefashion.MostofthereportedNZVItransportvehiclescan

onlyholdupto2.5g/Lofiron[1],whichlimitedthecosteffectivenessoftheremediationin

highlycontaminatedlands.MicroemulsioncanbeappliedasanalternativestabilizerforNZVIat

contaminantssitethatarenotsuitableforthecurrentNZVItechnology.

Forclosure,thisstudysuccessfullyassessedexaminedtwoNZVIstabilizationsystems.The

SDEHP-stabilizedNZVIisanimprovementbasedonthetransportimplicationsfromthe

microemulsion-stabilizedironoxidenanoparticles.Thisworkemphasizedtheimportanceof

stabilitytoNZVItransportintheporousmediaandhighlightedSDEHP-stabilizedNZVIasa

potentialcandidateforfuturegroundwaterremediation.

Page 97: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

89

4.2References:[1] C.M.Kocur,D.M.O’Carroll,andB.E.Sleep,“ImpactofnZVIstabilityonmobilityinporousmedia,”J.Contam.Hydrol.,

vol.145,pp.17–25,2013.

[2] M.Stefaniuk,P.Oleszczuk,andY.S.Ok,“Reviewonnanozerovalentiron(nZVI):Fromsynthesistoenvironmental

applications,”Chem.Eng.J.,vol.287,pp.618–632,2016.

[3] D.O’Carroll,B.Sleep,M.Krol,H.Boparai,andC.Kocur,“Nanoscalezerovalentironandbimetallicparticlesfor

contaminatedsiteremediation,”Adv.WaterResour.,vol.51,pp.104–122,2013.

[4] F.Fu,D.D.Dionysiou,andH.Liu,“Theuseofzero-valentironforgroundwaterremediationandwastewater

treatment:Areview,”J.Hazard.Mater.,vol.267,pp.194–205,2014.

[5] A.I.A.Chowdhury,M.M.Krol,C.M.Kocur,H.K.Boparai,K.P.Weber,B.E.Sleep,andD.M.O’Carroll,“NZVIinjection

intovariablysaturatedsoils:Fieldandmodelingstudy,”J.Contam.Hydrol.,vol.183,pp.16–28,2015.

[6] C.M.Kocur,A.I.Chowdhury,N.Sakulchaicharoen,H.K.Boparai,K.P.Weber,P.Sharma,M.M.Krol,L.Austrins,C.

Peace,B.E.Sleep,andD.M.O’Carroll,“CharacterizationofnZVImobilityinafieldscaletest,”Environ.Sci.Technol.,

vol.48,no.5,pp.2862–2869,2014.

[7] S.O’Hara,T.Krug,J.Quinn,C.Clausen,andC.Geiger,“FieldandlaboratoryevaluationofthetreatmentofDNAPL

sourcezonesusingemulsifiedzero-valentiron,”Remediat.J.,vol.16,no.2,pp.35–56,2006.

[8] Z.Wang,“SYNTHESISOFSTABLEANDREACTIVEMICROEMULSIFIEDZERO-VALENTIRONNANOPARTICLES(MENZVI)

USINGEXTENDEDSURFACTANT,”2015.

[9] Z.Wang,A.Lam,andE.Acosta,“SuspensionsofIronOxideNanoparticlesStabilizedbyAnionicSurfactants,”J.

SurfactantsDeterg.,vol.16,no.3,pp.397–407,2013.

[10] E.Wang,Ziheng;Choi,FrancisandAcosta,“EffectofSurfactantsonZero-ValentIronNanoparticles(NZVI)Reactivity.”.

Page 98: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

90

AppendixA–FerricChlorideBasedSodiumDiethylHexylPhosphate

(SDEHP)-stabilizedNZVI

A.1Introduction

NZVIcanbeartificiallysynthesizedfromtwomainsources,ferricchloride(FeCl3)andiron

sulfate(FeSO4)[1].Bothsourcesofiron,namelyferricsourceandsulfatesource,undergoa

reductionreactionwithNaBH4,reducingfromiron(II)sulfateandiron(III)chloridetothezero-

valentform,aslistedinthefollowing:

(1) 2𝐹𝑒Uw + 3𝐵𝐻qA + 3𝐻W𝑂 → 2𝐹𝑒a + 𝐻W𝐵𝑂UA + 4𝐻w + 2𝐻W

And

(2) 4𝐹𝑒Uw + 3𝐵𝐻A + 9𝐻W𝑂 → 4𝐹𝑒a + 3𝐻W𝐵𝑂A + 12𝐻w + 6𝐻W

respectively.Fromtheliterature,bothironsourceswereappliedextensivelyassynthesis

sourcesforNZVIstudieswiththeironsulfatebeingslightlyhigher[1]whilethechloridesource

wasthemostoriginalmethod.Itisalsoindictedthatironsulfateisconsideredamore

environmentalfriendlysourceofNZVIincomparisontoferricchloride[1].Inbothcases,bare

NZVIparticlesaresynthesizedwithidenticalpropertiessuchasinstabilityandatsizeswithin

similarrange.

Forimprovingthemobility,surfacemodifiersarecommonlyaddedtobareNZVIsuspensions.In

general,surfacemodifiersareappliedtoNZVIintwoways:1.Re-suspension[2]and2.

Synthesiswiththepresenceofthesurfacemodifiers[3].Inthere-suspensiontypesurface

modifications,thesourceoftheNZVImayplayanegligibleimpacttotheoverallsuspension;

however,someimpactsareexpectedwhentheNZVIsynthesistakesplacewiththemodifiers.

Page 99: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

91

Inspecific,thereactionsproductsfrombothferricandsulfatemethodmayinteractwiththe

surfacemodifiersandtheoverallsuspensiondifferently.Currently,therehasnostudies

focusedonthestabilityandmobilitydifferencebetweentheNZVIfrombothsources.In

chapter3,ironsulfate-basedNZVIparticlesweresynthesizedusingthe“one-pot”technique

andanalyzedatvarioussurfactantandNZVIconcentrations.AnNZVIformulationat100mM

SDEHPwasreportedtodemonstrateaprolongedofover2monthswithexcellentmobilityin

porousmedia.ItisobservedthatwithdifferentsourcesofNZVIappliedinthe“one-pot”

synthesismethoddescribedinthisthesis,differentqualityofNZVIsuspensionswereobtained.

Theobjectiveofthisworkistoinvestigatethebasicproperties,suchasstabilityandsizesof

ferricchloride-based,SDEH-stabilizedNZVIformulationsincomparisontotheiron-sulfate

basedformulation.Thesecondaryobjectiveistodeterminethecausebehindthedifferences

betweenchlorideandsulfatesynthesisinSDEHP-stabilizedNZVI.

A.2Methodology

Unlessotherwisespecified,allproceduresandmaterialsareconductedandpreparedatroom

temperatureandconditions.

A.2.1PreparationofSurfactantSDEHPandFeCl3-basedNZVI

TheprocedureofsynthesizingSDEHPisdescribedinsection3.2.1andadaptedfromprocedure

ofLuanetal.[4]TheNZVIwassynthesizedinthesame“one-pot”synthesisfashionasdescribed

insection3.2.2withthefundamentalideaadaptedfromWantetal.[5]

A.2.2FormulationdesignofFeCl3-basedNZVI

Surfacetensionmeasurementwasappliedtodeterminethecriticalmicelleconcentration

(CMC)ofSDEHPwith1g/LNZVIequivalenceofferricchloridedissolved.Themeasurementwas

Page 100: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

92

conductedwithatensiometeratdifferentconcentrationsofSDEHP.Detailedprocedureis

describedinsection3.2.4.

A.2.3CharacterizationAnalysis:SizeandStability

Transmissionelectronicmicroscope(TEM)anddynamiclightscattering(DLS)areusedto

analyzeparticleandhydrodynamicsizes,respectively.Samplepreparationforbothsizeanalysis

isdescribedinsection2.3.4.Forstabilityanalysis,identicalprocedurewasfollowedas

describedinsection2.3.3.

A.3ResultsandDiscussions

A.3.1FormulationDesignImplication

BasedontheformulationdesignframeworkproposedbyWangetal.,theconcentrationofthe

surfactantmustbehigherthantheCMCtoachievehigherstability[6].Theapproachwas

reportedsuccessfulwithprolongedstabilityinthesulfate-based,SDEHP-stabilizedNZVIat1

g/L,100mMsurfactantconcentration.FigureA1showsthesurfacetensionmeasurementsat

differentconcentrationofSDEHP.TheCMCisidentifiedatabout35mMbasedonthe

interpretationofline-of-the-best-fit.TheCMCoftheferricchloridedissolvedSDEHP(35mM)is

lowerthanironsulfatedissolvedSDEHP(57mM).Thisimpliesthebindingofthesurfactantand

ironaredifferentinthetwocasesduetothepresenceofanions,chlorideorsulfate.Inthecase

ofthesulfatemethod,thehigherCMCcanbeexplainedbythepossibilitythatthesurfactants

aremorelikelytobindtothesurfaceoftheiron,leavinglessfreesurfactantstoformempty

micelles.Ontheotherhand,thehigherCMCinthechloridemethodimpliestheopposite,the

surfactantislesslikelytobindontothesurfaceoftheiron,thusmorefreesurfactantsare

availabletoformmicellesatthesameconcentrations.TherootcauseofthedifferenceinCMC

Page 101: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

93

ishowever,unclear,itissuspectedthatthepresenceofthedifferentionsorthedifferencein

theironcharges.Thisisexpectedtohavesomeimpactstothestabilityaftertheproductionto

theformulation.

FigureA1.FigureA1.SurfacetensionmeasurementsofSDEHPatvariousconcentrationwith

ironchloride(1g/LequivalenceofNZVI)dissolved.

A.3.2StabilityandSizeAnalysis

FigureA2.showsthestabilitytimelapsephotoat1hourofchloridemethodbased,SDEHP-

stabilizedNZVIat30,50and100mM.Allthethreeconcentrationsexperiencedaggregation

andsedimentafteronehouruponsynthesis.Outofthethree,100mMSDEHPdemonstrated

lesssettlingthanthe30and50mM,implyingthathigherconcentrationofSDEHPmayimprove

15

20

25

30

35

40

45

50

1 10 100

SurfaceTension(m

N/M)

SDEHPConc.(mM)-LogScale

SurfaceTensionofSDEHPwith1g/LFeCl3Dissolved

Page 102: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

94

thestabilityinthecaseofchloridebasedmethod.Incontrast,atthesameconcentrationof

NZVIandSDEHP,sulfatemethoddemonstratedastabilityofover2months.Thedifferencein

thesynthesiscanberelatedtotheCMCdifferencediscussed,wheremolecularlythe

interactionsbetweentheanions,surfactantandironaredifferentbetweenthesulfateand

chloridemethod.Furthermore,thereactionfromthechloridemethodproducesabout3times

morehydrogenionsthanthesulfatemethod.ThismeansthatthepHlevelofthechloride

methodNZVIsuspensioncanbealotlowerthanthepHofthesulfatemethod.Thedecreasein

pHisreportedtoimpactthezetapotentialthuscontributiontolowerstability.

Forsizeanalysis,figure3showstheTEMimagingoftheNZVIparticlesizeofthesynthesized

NZVIat100mM.Overall,thehardparticlesizeofthechloridebasedNZVIisabout100-200nm,

whichisinthesamerangetothereportedvalueinChapter3.However,thesurfactantcoating

aroundtheNZVIisalotmoreemphasizedincomparisontotheTEMimagingforthesulfate

method.Thisisreflectedinthehydrodynamicdiameterofthechloridemethod-basedNZVIas

well.Assummarizedintable3.2,thehydrodynamicdiameterfor30,50and100mMSDEHPare

400,420and380,respectively.Theyarefarlargerthanthesulfatemethod-basedNZVIas

reportedinChapter3.Thedifferenceinhydrodynamicsizemayimpliedthedifferencein

molecularinteractionbetweenthechlorideandthesurfactant.Thiscouldbeanimplicationon

themechanismforsurfactantsuspendingandtheformationofwormlikemicelle.

Page 103: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

95

[email protected]/Lofiron

concentration.1houraftersynthesis.

A.4FutureWorks

Differentstabilitybehavioursareobservedforchloride-andsulfate-basedNZVIunderthesame

synthesiscondition.Thisappendixprovedthatwithdifferentsourcesofironanddifferent

reactionpathways,synthesiswiththepresenceofsurfacemodifiers.Fromthestudy,itis

shownthatthesulfatemethodismoreinfavouroThiscouldbeanimplicationon

improvementsofotherNZVIsurfacestabilizationsandmobilityinporousmedia,onecan

improvetheabilityoftheNZVIsuspensionbychangingthesourceofsynthesisiron.Itis

Page 104: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

96

importanttoalsonotethatwhetherthetwoironsourceswilldemonstrateanydifferencein

reactivityduetothedifferenceinsynthesisreactions.

Page 105: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

97

A.5References:

[1] W.ZhangandD.W.Elliott,“Applicationsofironnanoparticlesforgroundwaterremediation,”Remediat.J.,vol.16,no.

2,pp.7–21,2006.

[2] J.Soukupova,R.Zboril,I.Medrik,J.Filip,K.Safarova,R.Ledl,M.Mashlan,J.Nosek,andM.Cernik,“Highly

concentrated,reactiveandstabledispersionofzero-valentironnanoparticles:Directsurfaceandsiteapplication,”

Chem.Eng.J.,vol.262,pp.813–822,2015.

[3] S.Z.Yu,Y.Cheng,X.F.Fan,andL.P.Xu,“PreparationofCoatedCMC-nZVIUsingRheologicalPhaseReactionMethod

andResearchonDegradationofChloroforminWater,”Mater.Sci.Forum,vol.847,pp.230–233,2016.

[4] Y.Luan,G.Xu,S.Yuan,L.Xiao,andZ.Zhang,“Comparativestudiesofstructurallysimilarsurfactants:Sodiumbis(2-

ethylhexyl)phosphateandsodiumbis(2-ethylhexyl)sulfosuccinate,”Langmuir,vol.18,no.22,pp.8700–8705,2002.

[5] Z.WangandE.Acosta,“FormulationdesignfortargetdeliveryofironnanoparticlestoTCEzones,”J.Contam.Hydrol.,

vol.155,pp.9–19,2013.

[6] Z.Wang,A.Lam,andE.Acosta,“SuspensionsofIronOxideNanoparticlesStabilizedbyAnionicSurfactants,”J.

SurfactantsDeterg.,vol.16,no.3,pp.397–407,2013.

Page 106: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

98

AppendixB:ComparisonbetweenCarboxylmethyl-celluosestabilized

ironoxidenanoparticleswithmicroemulsion-stabilizednanoparticles

B1.Background:Carboxylmethyl-celluose(CMC)isbyfarthemostsuccessfulNZVIstabilizerintheliterature.The

mobilityofCMC-stabilizedNZVIhadwelltestedinthelabscaleandfullscaleremediationwas

launchedin2014.Inthissection,amobilitycomparisonbetweenCMC-stabilizedironoxideand

microemulsionironoxidewastestedfollowingidenticalexperimentalsetupdescribedin

chapter2.TheformulationofCMC-stabilizedNZVIwasmodifiedfromtheonedescribedby

Kocuretal.(2.5g/Lofiron,CMCMW=90,000at0.8wt%)[1]withNZVIbeingreplacedbyiron

oxideforconsistencyofcomparison.2.5g/Lequivalenceofironoxidewassuspendedinthe

50%dilutedmicroemulsionformulationasdiscussedinchapter2.

B2.Results:

B2.1.StabilityThestabilityofmicroemulsionandCMC-stabilizedironoxideat2.5g/Lwerecomparedusing

timelapsephotoscomparisons.AsindicatedinfigureB1,CMC-stabilizedironoxidestartedto

showsignsofaggregationandparticlesettlingafter15hours.Majorsedimentationwas

observedatthebottomofthevialforCMC-stabilizedironoxideafter80hours.Ontheother

hand,nosignificantsettlingwasobservedwithmicroemulsionironoxide,consistenttothe

Page 107: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

99

findingsinchapter2.Thisindicatedthatmicroemulsionironoxideholdsamuchstronger

stabilitythanCMCironoxide.Theminimumsettlingandaggregationimpliedthat

microemulsion-basedironsuspensionexperienceasmoothertransportprocessinsandin

comparisontoCMC-basedironparticles.

A.

FigureB1.A.TimelapsedphotosofCMCandmicroemulsionstabilizedironoxideat2.5g/L.B.

EvidenceofsettlingofCMCironoxideafter80hoursuponsuspension.

Page 108: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

100

B2.2.MobilityComparisonTransportstudywasconductedonbothmicroemulsionironoxideandCMCironoxideat2.5

g/L.Forthemicromeulsionironoxidetransportat2.5g/L,thetransportresultwasreproducible

comparingtothetransportresultsinchapter2.ForCMCironoxide,despitesuccessful

completionoftheexperimentanddataanalysis,abreakthroughcurvewasnotabletobe

obtained.However,fromthepostanalysessuchaspressuredropmonitoringandsandgrain

analysis,itcanbeconfirmedthatmicroemulsionironoxidedemonstratedbettertransportthan

CMCironoxide.

Pressuredropwasrecordedateveryporevolumeduringtheflushingstage(foratotalof5

porevolumes).FigureB2demonstratedthepressuredropmoniroingresultcomparison

betweenCMCandmicroemulsionironoxide.Thepressuredropmonitoringresultshowsthat

CMCironoxidestartedwithahighpressuredropof22.5psiandlinearlydecreasedto3psi

whilemicroemulsionironoxideremainedat0.5psithroughouttheflushingstage.Thisimplies

thatduringthetransportofCMCNZVI,potentialcloggingofthesandporesincreasedthe

difficultyofflowinthecolumn,thusexperiencingahighpressuredropinthebeginning.The

decreaseinthepressuredropmayimplythatthecloggedparticleswerebeingflushedoutof

thecolumnandthusinferredreversibleadsorptionoftheironparticles.Ontheotherhand,

microemulsionironoxidedemonstratednegligiblepressuredropintheflushingstage,implying

minimumcloggingandretentionoftheparticles.

Page 109: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

101

FigureB2.Comparisonofpressuredropmonitoringresultsatthepost-flushingstagebetween

CMCandmicroemulsionironoxide.

SimilarironretentionanalysiswasconductedafterthecolumnstudyforCMCand

microemulsionironoxideasdemonstratedinfigureB3.FigureB3showsconsistentresultsand

conclusionasfigureB2,whereCMCironoxideexperiencedmoreretentionanddifficulties

duringtransport.InfigureB3,CMCironoxidedemonstratedadecreasingtrendintheiron

retentionanalysissimilartotheresultsofscheduleBinchapter2.Whereasmicroemulsioniron

oxidedemonstratedreproducibleresultstoscheduleA.Thisagainconfirmsthehypothesisthat

duetoinstabilityoftheCMCironoxide,moreretentionofironwasobserved.

0

5

10

15

20

25

13 14 15 16 17 18 19 20

PressureDrop(Psi)

PoreVolumeInjected

PressureDropMonitoring- PostFlushingStage

ME CMC

Page 110: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

102

A.

B.

FigureB3.Iron-sandgrainanalysiswithmicroscopepicturesforA.Microemulsionironoxideat

2.5g/LandB.CMCironoxideat2.5g/L.

Page 111: Transport and Development of Microemulsion- and Surfactant ... · Microemulsion-Stabilized Iron Nanoparticles in Porous Media Dennis Hsu Masters of Applied Science Graduate Department

103

B3.References:

[1] C.M.Kocur,D.M.O’Carroll,andB.E.Sleep,“ImpactofnZVIstabilityonmobilityinporousmedia,”J.Contam.Hydrol.,

vol.145,pp.17–25,2013.