Research Article Adsorption and Photocatalytic ...

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2013 Article ID 138918 10 pageshttpdxdoiorg1011552013138918

Research ArticleAdsorption and Photocatalytic Decomposition of the 120573-BlockerMetoprolol in Aqueous Titanium Dioxide Suspensions KineticsIntermediates and Degradation Pathways

Violette Romero Pilar Marco Jaime Gimeacutenez and Santiago Esplugas

Department of Chemical Engineering University of Barcelona CMartı i Franques 1 08028 Barcelona Spain

Correspondence should be addressed to Pilar Marco pmarcoubedu

Received 28 May 2013 Revised 25 September 2013 Accepted 3 October 2013

Academic Editor Manickavachagam Muruganandham

Copyright copy 2013 Violette Romero et alThis is an open access article distributed under theCreativeCommonsAttribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

This study reports the photocatalytic degradation of the 120573-blocker metoprolol (MET) using TiO2suspended as catalyst A series of

photoexperiments were carried out by a UV lamp emitting in the 250ndash400 nm range providing information about the absorptionof radiation in the photoreactor wall The influence of the radiation wavelength on the MET photooxidation rate was investigatedusing a filter cutting out wavelengths shorter than 280 nm Effects of photolysis and adsorption at different initial pH were studiedto evaluate noncatalytic degradation for this pharmaceutical MET adsorption onto titania was fitted to two-parameter Langmuirisotherm From adsorption results it appears that the photocatalytic degradation can occur mainly on the surface of TiO

2 MET

removed by photocatalysis was 100 conditions within 300min while only 26 was achieved by photolysis at the same time TiO2

photocatalysis degradation of MET in the first stage of the reaction followed approximately a pseudo-first-order model The majorreaction intermediates were identified by LCMS analysis such as 3-(propan-2-ylamino)propane-12-diol or 3-aminoprop-1-en-2-ol Based on the identified intermediates a photocatalytic degradation pathway was proposed including the cleavage of side chainand the hydroxylation addition to the parent compounds

1 Introduction

The presence of pharmaceutical drugs and endocrine disrup-tors in surface ground and drinking waters is a growingenvironmental concern [1ndash9] This pollution is caused byemission from production sites direct disposal of surplusdrugs in households excretion after drug administration tohumans and animals wastewater from fish and other animalfarms and industry [3 10 11] Some of these drugs as 120573-blockers have been detected in the order of ng Lminus1 to 120583g Lminus1in the water [3ndash9 12] As an example metoprolol tartrate salt(MET) which is usually prescribed as antihypertensive orantiarrhythmic has been quantified up to 2 120583g Lminus1 in sewagetreatment plant (STP) effluents and to 240 ng Lminus1 in rivers[13] Metoprolol and atenolol together account for more than80 of total 120573-blockers consumption in Europe [6] Duringthe last years metoprolol usage increased by a factor of 4probably due to a change in human behavior [6] Althoughfull ecotoxicity data are not available [13 14] it has been

shown that they can adversely affect aquatic organisms evenat low concentration [2] Due to its widespread occurrenceand potential impact MET must be removed from treatedwater before discharge or reuse

Several treatments for the removal of these compoundshave been reported in the literature including membranefiltration [15] activated carbon adsorption [16] and reverseosmosis [17 18] However the conventional water treat-ment processes are relatively inefficient in treating thesecompounds [4 19] These pharmaceuticals can undergoabiotic degradation (hydrolysis photolysis) [13] and most ofthem are photoactive because their structural compositionsconsist of aromatic rings heteroatoms and other functionalgroups that can absorb solar radiation [20] Thus sunlightinduced photochemical treatments should be considered asan alternative to traditional treatment Several researcheshave demonstrated that MET shows slow direct phototrans-formation andor hydrolysis [13 21 22] In this contextadvanced oxidation processes (AOPs) appear as a good

2 International Journal of Photoenergy

012345678910

0

5

10

15

20

25

200 250 300 350 400 450 500Wavelength (nm)

MetoprololLamp

Abso

rban

cetimes10minus2

f(120582)

(mEi

nste

into

tal E

inste

in)

Figure 1 Absorbance spectrum of MET for aqueous concentrationof 10mg Lminus1 (left axis) and lamp spectrum (right axis) where 119891(120582)represents the spectral distribution of the lamp

alternative for its degradation due to their versatility andability to increase biodegradability [23 24] Among thedifferent advanced oxidation processes heterogenous photo-catalysis has been a potential alternative for the degradationof hazardous pollutants Oxidation of organic compounds bymeans of TiO

2was achieved by hydroxyl radical generation

through the 119890minusℎ+ pair generated when the semiconductor isexposed to UV radiation [11 14]

The main objective of this investigation is to undertake astudy on the heterogeneous photocatalytic degradation andmineralization of MET in aqueous suspensions with TiO

2

In addition the contribution of the degradation of METby direct photolysis and the adsorption of the metoprololonto TiO

2were studied In this way the effect of different

initial pH values on the photodegradation rate and theadsorption isotherms of metoprolol in TiO

2suspensions

were determined The contribution of direct photolysis inphotocatalysis was also examined in detail by using differentwavelengths and glass type photoreactors Additionally anattempt has been completed to estimate the kinetic param-eters and to identify the main intermediates formed duringthe photocatalytic degradation of MET

2 Materials and Methods

21 Chemicals and Reagents Metoprolol tartrate (MET) saltwas purchased fromSigmaAldrichChemical Co (Spain) andused as received (1-[4-(2 methoxyethyl)phenoxy]-3-(propan-2-ylamino)propan-2-ol tartrate (21) CAS no 56392-17-7(C15H25NO3)2C4H6O6 MW 68481) Solutions of 50mg Lminus1

of MET were prepared using deionized water to assureaccurate measurements of concentrations to follow theTOC to secure identification of intermediates and to makepredictions about possible mechanisms of photocatalysisFor pH adjustment 01mol Lminus1 sulphuric acid or 01mol Lminus1sodium hydroxide was used All chemicals were HPLC grade

and they were used without further purification Titaniumdioxide (TiO

2) Degussa P-25 (commercial catalyst sim70

anatasesim30 rutile surface area 50plusmn 50m2 gminus1 and 300120583mparticle size [25]) was used as received This TiO

2is a

photochemical stable material [6 26 27]

22 Analytical Instruments The target compounds con-centrations were monitored by a high-performance liquidchromatograph (HPLC) from Waters using a SEA18 5 120583m15 times 046 Teknokroma column and Waters 996 photodiodearray detector using Empower Pro software 2002 Water CoThe mobile phase was composed by water and acetonitrile(20 80) injected with a flow-rate of 085mLminminus1 anddetected at maximum metoprolol (2219 nm) Total organiccarbon (TOC) was measured in a Shimadzu TOC-V CNSpH was measured by a Crison GLP 22 instrument UV-VIS spectra of MET (Figure 1) were obtained for 10mg Lminus1aqueous solution on a PerkinElmer UVvis Lambda 20 (200ndash400 nm range) spectrophotometer

23 Experimental Procedure Photodegradation experimentswere conducted in a Solarbox (COFOMEGRAMilan Italy)and equipped with a Xenon lamp (Phillips XOP 1000W)and a tubular-horizontal photoreactor (0084L illuminatedvolume) located at the axis of a parabolicmirror in the bottomof the Solarbox The photon flux inside the photoreactorwas evaluated by o-nitrobenzaldehyde actinometry [28 29]being 268120583Einstein sminus1 A stirred reservoir tank (10 L) wasfilled with the pharmaceutical-TiO

2(suspended) aqueous

solution The solution was continuously pumped (peristalticpump Ecoline VC-280 II Ismatec) to the equipment andrecirculated to the reservoir tank with a flow of 065 Lminminus1In order to keep the solution at 25∘C the jacket temperature ofthe stirred tank was controlled with an ultrathermostat bath(Haake K10) Samples were taken every 30 minutes during300 minutes and quickly analyzed Before HPLC analysissamples were filtered through 020120583m PVDF membrane toseparate TiO

2 All the experiments were duplicated and the

results presented were the mean valuesAccording to the literature [13] metoprolol stability

in aqueous solution was previously verified by storing50mg Lminus1 during 3 days in the dark at room temperature andno degradation was observed

MET adsorption of TiO2was also measured Thus MET

solution (0 to 50mg Lminus1) was prepared with TiO2in suspen-

sion (04 g Lminus1) and placed into 25mL hermetic closed flasksadjusting the pH with NaOH solution (01mol Lminus1) Theconical flasks were shaken at a constant speed of 100 rpm andat room temperature (25 plusmn 05∘C) Samples were taken every24 h assuming that adsorption equilibrium was reached

For the identification of byproducts the final samplemixture at 300 minutes was analyzed by electrospray ion-izationmass spectrometry using a PerSeptive TOF MarinerJascoo AS-2050 plus ISmass spectrometer into the119898119911 rangeof 50ndash1000 The experiments were carried out in replicate

International Journal of Photoenergy 3

00

05

10

15

20

25

30

0

5

10

15

20

25

30

0 80 160 240 320

Rem

oval

MET

()

t (min)

TOC

TOC

o

Figure 2 MET photodegradation removal (I) and TOCTOCo (∙)under simulated UV

3 Results and Discussion

31 Effect of UV Radiation Photolysis on Metoprolol Degra-dation When studying photocatalysis it is very importantto be able to separate the influence of photolysis since it isexpected to tackle the degradation of the substances mainlyinduced by the action of the catalyst For this purpose aseries of experiments was done with UV illumination andwithout catalyst to highlight the metoprolol ability to absorbthe radiation reaching the system

Figure 2 shows the results obtained after applying sim-ulated sunlight As observed MET is not fast enough to bephotodegraded in water by direct photolysis [30] only 26of MET in 300 minutes was degraded under simulated UVMoreover it shows that direct photolysis was not able toproduce MET mineralization at the experimental conditionstested This behavior can be explained because the METabsorption spectrum overlaps only slightly the spectrum ofthe incoming radiation (Figure 1)

The UV-VIS absorbance was used to calculate the molarabsorption coefficient (120576) of the metoprolol at a wavelengthof 2219 nm (Figure 1) assuming that Beer-Lambertrsquos law isfollowed

119860 = minus log (119879) = 120576 times 119897 times 119862 (1)

where 119860 is the absorbance (measured directly by the spec-trophotometer)119879 is the transmittance 120576 is themolar absorp-tion coefficient 119897 is the distance that the light travels throughthe material and 119862 is the concentration of pollutant Themolar absorption coefficient (120576) was 281 Lmolminus1 cmminus1 thisvalue is very similar to other reported values [12 13]This lowvalue explains the MET stability in direct photolysis condi-tions Nevertheless different studies [12 13 31] show a highphotoability of some 120573-blockers for example propranololnadolol and alprenolol The rapid photodegradation of thesecompounds was supported by a high molecular absorptioncoefficient (120576 gt 800 Lmolminus1 cmminus1) This confirmed thehypothesis that photoinitiated reactions contribute to thedegradation of naphthalene backbone (ie propranolol) [32]whereas the metoprolol having a benzoic skeleton is notsensitive to direct photolysis when dissolved in deionizedwater [33]

0 10 20 30 40 50 60

Free pHpH 9

q(m

g gminus1)

12E minus 02

10E minus 02

80E minus 03

60E minus 03

40E minus 03

20E minus 03

00E + 00

C (mg Lminus1)

Figure 3 Effect of pH on adsorption of MET over TiO2at 25∘C pH

9 (∙) and free pH (I)

The efficiency of the photochemical transformation pro-cess depends on many factors such as the irradiation setupsthe characteristics of the light source the water matrixused the initial concentration and the pH of the solutions[31] Tests were carried out using different photoreactorsa borosilicate Duran and quartz glass reactor cutting outwavelengths shorter than 290 and 320 nm respectively Otherexperiments have been done with and without glass filter forrestricting transmissions of light below 280 nm

In this study the effect of borosilicate Duran and quartzglass material reactor has been investigated under UV radi-ation It was observed that MET removal was 25 and 28and the TOC reduction was 360 and 162 for reactorsmade with borosilicate Duran and quartz respectively Thusalthough the mineralization was not significant there is asmall photodegradation of MET for the two tested reactorsafter 300 minutes of reaction Moreover the effect of a filterglass cutting out wavelengths shorter than 280 nm has beeninvestigated As a result only 19 ofMET in 300 minutes hasbeen removed with the glass filter however MET removalof 25 can be achieved without filter glass TOC conversionwas 637 and 360with andwithout filter correspondinglyafter 300 minutes thus confirming that the mineralization isvery low in both cases

Summarizing UV irradiation in the absence of TiO2

achieved an MET degradation lower than 30 after 300minutes of irradiation confirming that the direct photolysisis not fast enough to be considered as an adequate technology

32 The Role of the Adsorption on the Photocatalytic Degrada-tion Since the adsorption can play an important role in theevolution of the photodegradation adsorption experimentsat constant temperature (25 plusmn 05∘C) were carried out Theadsorption capacity of MET 119902

119890(mg gminus1) was calculated

from the difference in MET concentration in the aqueousphase before and after adsorption at different initial METconcentrations (0 62 125 25 375 and 50mg Lminus1) Thevariation in adsorption of MET onto TiO

2was studied at two

pHs 9 and free pH (pH asymp 58) Figure 3 presents the obtained

4 International Journal of Photoenergy

Table 1 Isotherm parameters for MET adsorption onto TiO2 obtained by linear method at 25∘C

Two-parameter model Parameters pHFree 9

Langmuir

119902119890=

119902119898119870119886119862119890

1 + 119870119886119862119890

119902119898(mol gminus1) 00014 00250

119870119871(Lmolminus1) 00930 00817

1198772 0987 0998

Freundlich119902119890= 119870119865119862119890

1119899

1119899 0244 0670119870119865(Lmolminus1) 000042 000129

1198772 0105 0147

Temkin

119902119890=119877119879

119887ln (119870119879+ 119862119890)

119877119879119887 000024 000508119870119879(Lmolminus1) 2718 0962

1198772 0604 0982Dubinin-Radushkevich

119902119890= 119902119863exp(minus119861

119889[119877119879 ln(1 + 1

119862119890

)])

119902119863(mol gminus1) 00013 00233

119861119863times 10minus3 (mol2 kJminus2) 1533 1532

1198772 0835 0778Three-parameter model

Redlich-Peterson

119902119890=

119870RP119862119890

1 + 119886119877119862119890

120573

119870RP (Lmolminus1) 000011 010119886119877(Lmolminus1) 0051 18040

120573 0999 06791198772 0826 0789

Langmuir-Freundlich

119902119890=

119870LF119862119899LF119890

1 + (119886LF119862119890)119899LF

119870LF (Lmolminus1) 0000205 000809119886LF (Lmolminus1) 0134 0310119899LF 0779 0921198772 0211 0734

results and indicates that the amount adsorbed increaseswhen pH does it

The increase in the adsorption ofmetoprololwith increas-ing pH can be elucidated by considering the surface charge ofthe adsorbentmaterial (pHpzc sim 65) [13 34]That is titaniumdioxide surface is positively charged in acid media pH (pH le7) whereas it is negatively charged under alkaline conditions(pH ge 7) [29 35] Also metoprolol can be transformedto MET anion in the basic pH (pH sim 10) since the pKavalue of metoprolol is 97 [36] Under free pH conditionsclose to the point zero charge of TiO

2(65) [30] MET is

positively charged A low adsorption was observed due tono electrostatic attraction between the surface charge andMET A highest adsorption between MET and TiO

2would

be observed at pH 9 because the negative charges of thesurface of the catalyst attract the protonated MET form Inaddition the photocatalytic degradation would be expectedon the surface of the catalysis

Two-parameter isothermmodels (Langmuir FreundlichTemkin and Dubinin-Radushkevich) and three-parameterisotherm models (Redlich-Peterson and Langmuir-Freundlich) were tested in the fitting of the adsorptiondata of MET onto titanium dioxide [37 38]

119870119886 119870119865 119870119879 119870RP and 119870119871 are the Langmuir Freundlich

Temkin Redlich-Peterson and Langmuir-Freundlich adsorp-tion equilibrium constants (Lmolminus1) respectively 119886

119877and

119886LF are also the Redlich-Peterson and Langmuir-Freundlcih

constants (L molminus1) respectively 119862119890and 119902

119890are the equilib-

rium concentration (mol Lminus1) and the adsorption capacity(mol gminus1) respectively 119902

119863is the Dubinin-Radushkevich

saturation capacity (mol gminus1) The parameter 119902119898represents

the maximum monolayer adsorption capacity (mol gminus1) and1119899 the adsorption intensity which provides an indication offavorability and capacity of the adsorbentadsorbate systemThe parameter 119887 is related to the adsorption heat119861

119863gives the

mean adsorption free energy 119864119863(kJmolminus1) The parameters

120573 and 119899LF are the Redlich-Peterson and Langmuir-Freundlichexponents which lie between 0 and 1 [39] And 1198772 is thecorresponding sum of squares error obtained in the fittingexperimental data of each model

From Table 1 it was observed that the best fitting wereobtained for Langmuir isotherm (1198772 = 0987 and 0998 forfree pH and pH 9 respectively)Thus these models representthe equilibrium adsorption of MET on TiO

2particles in the

range of concentration studied Accordingly the adsorptionmechanism may be interpreted as a monolayer coverage ofthe catalyst surface

For free pHMET adsorption (119902119898) was lower than for pH

9 00014mol gminus1 and 00250mol gminus1 respectively In thesecases the adsorption does not play an important role in thephotocatalytic process TheMET percentage removal in darkconditions was 01 and 11 for free pH and pH 9These lowadsorption values andMET percentage removals suggest that

International Journal of Photoenergy 5

Table 2 Kinetics of metoprolol UV-C photodegradation under different conditions

Glass material reactor Glass filter 120582 ge 280 nm pH 11990512

(h)

PhotolysisBorosilicate with 58 plusmn 1 165 plusmn 05

without 58 plusmn 1 116 plusmn 06

Quartz without 58 plusmn 1 105 plusmn 05

Photocatalysis Borosilicate without 58 plusmn 1 081 plusmn 04

without 90 plusmn 1 058 plusmn 03

the most possible way of degradation could be reached bymigration of ∙OH radicals to the bulk of the suspension

33 Degradation of MET by Photocatalytic Process The pho-tocatalytic degradation of MET solution (50mg Lminus1) wascarried out during 300 minutes in the presence of 04 g Lminus1of TiO

2under UV-VIS light at room temperature It is know

that in heterogeneous photocatalysis the rate of degradationis not always proportional to the catalyst load [40] Anoptimal point exists where TiO

2loaded shows a maximum

degradation rate Previous studies carried out in our researchgroup reported that the optimum catalyst concentration was04 g Lminus1 [41] Over this value scattering can appear andtherefore increase in degradation rate does not occur

Firstly the solution mixture was stirred for 24 hourswithout irradiation in order to get the equilibrium of METadsorption

Figure 4 depicts the photocatalytic degradation of METat free pH and pH 9 Maximum conversions are achievedat 240 and 300 minutes for pH 9 and free pH respectivelyAn important remark is that the initial removal rate for freepH and pH 9 experiments is different being higher at pH9 The effect of pH on the conversion is a complex issuerelated to the ionization states of the catalyst surface and thesubstrate as well as the rate of formation of radicals and otherreactive species in the reactionmixture [42]These effects canbe assessed since the action of the holes is favored at acidicconditions while hydroxyl radicals become the dominantspecies at neutral and alkaline conditions [42]

As known photocatalysis occurs through the energyadsorption by the catalyst (light between 200 and 400 nm forTiO2) Under excited condition the valance band-electron is

transferred to the conduction band forming the hole-electronpair (ℎ+119890minus) (2)The hydroxyl radicals are formed by cleavageof adsorbed molecules of water [43]

TiO2+ ℎ120574 997888rarr TiOlowast

2(ℎ+

119890minus) (2)

ℎ+ +H2O 997888rarr ∙OH +H+ (3)

If organic compounds are absorbed on the surface of thecatalyst the ∙OH nonselective attack promotes the cleavageof compounds boundsThe higher MET degradation and thelow MET adsorption on catalyst at a pH 9 suggest that the∙OH attack in the bulk of solution can be responsible for theMET degradation [40 44]

The values of TOC during the photocatalytic degradationof MET at two different pHs are given in Figure 4 The TOC

0

10

20

30

40

50

60

70

0102030405060708090

100

0 50 100 150 200 250 300

Rem

oval

TO

C (

)

Free pH (MET removal)pH 9 (MET removal)Free pH (TOC removal)pH 9 (TOC removal)

Rem

oval

MET

()

t (min)

Figure 4 MET and TOC removal () versus time (min) at free pHand pH 9 in photocatalytic experiments

7476

92102

116

118

120

134

161 193

208

220

226238

240 268 300 316332

0

2

4

6

8

10

12

14

16

65 80 100 116 134 155 175 197 217 238 260 280 305 325 345

Inte

nsity

(cps

)times105

mz (Da)

Figure 5 MS spectrum of major oxidation products of metoprolol

increases with time indicating the increasing mineralizationof the initial organic structures

34 Kinetics of MET Degradation The Langmuir-Hinshel-wood (L-H) model is usually used to describe the kinetics ofphotocatalytic degradation of organic pollutants [12 13 3031 41 45] being the kinetic equation expressed as

119903 = minus119889119862

119889119905=119870ads sdot 119896H-L sdot 119862

1 + 119870ads sdot 119862 (4)

6 International Journal of Photoenergy

Table 3 Intermediates proposed for the photocatalytic degradation of MET

Detectedcompound (DP)

Ret time(min) 119898119911 (Da) Molecular

formula Proposed structure

Metoprolol 324 268 C15H25NO3

O

O NH

HO

CH3

CH3

H3C

1 259 74 C4H11N

OH

H2CNH2

2 324 76 C3H9NO

HO

H3CNH2

3 259 92 C3H9NO2 HO

HO

NH2

4 259 102 C5H11NONH

O

HCH3

CH3

5 259 116 C6H13NONH

O

CH3

CH3

H3C

6 324 118 C6H15NONH

H3C

OH

CH3

CH3

7 259 120 C5H125NO2

NH

OH

CH3

CH3

HO

8 259 134 C6H15NO2

NH

OH

CH3

CH3HO

9 323 161 C11H12O

OCH3

H2C

10 323 193 C12H16O2

O

O

H3CCH3

International Journal of Photoenergy 7

Table 3 Continued

Detectedcompound (DP)

Ret time(min) 119898119911 (Da) Molecular

formula Proposed structure

11 324 208 C12H17NO2

O

O

H3C

NH2

12 303 220 C13H17NO2

O

O

H

NH

CH3

CH3

13 303 226 C12H19NO3

O

O NH2

H3C

OH

14 471 238 C13H19NO3

O NH

O

H

CH3

CH3

OH

15 323 240 C13H21NO3

O NH CH3

CH3HO

OH

16 398 300 C15H25NO5

O

O NH

HO

(OH)2

H3C

CH3

CH3

17 398 316 C13H25NO6

NH

O

O

HO

(OH)3

H3C

CH3

CH3

18 323 332 C13H19NO7

O

O NH

HO

(OH)4

H3C

CH3

CH3

where 119903 is the degradation rate 119862 is the reactant concentra-tion 119905 is the time 119896H-L is the rate constant and 119870ad is theadsorption equilibrium constant

Thismodel assumes that adsorption is a rapid equilibriumprocess and that the rate-determining step of the reactioninvolves the species present in amonolayer at the solidndashliquidinterface Furthermore if the adsorption of MET onto the

surface of the photocatalysts is very low 119870ads sdot 119862 can beneglected in the denominator simplifying the equation to apseudo-first-order equation as given by [46]

119903 = minus119889119862

119889119905= 119870ads sdot 119896H-L sdot 119862 = 119896 sdot 119862 (5)

8 International Journal of Photoenergy

O

O

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

OH

O

O

MET

O

O

O

ObullOH

O

NH

NH NH

NH

NH

NH

NH

NH

NH

NH

NH

NH

DP 2 DP 2

DP 4 DP 3

DP 8

DP 16

DP 17DP 15

DP 13

DP 10

DP 9

DP 11

DP 14

DP 12

DP 18

DP 6DP 5

O

O

O

H

O

O

H

O

O

O

O

O

O

O

bullOH ox

O

H

HO

HO

HO

HO

HO

CH3

CH3

CH3

CH3

CH3

H2CH3C

NH2

NH2 NH2

NH2

NH2

minusC3H8

minusC3H8 minusC3H8

minusC3H8

H2C

H3C

H3CH3C

H3C CH3CH3

CH3

CH3

CH3

CH3

CH3

CH3

minusC9H10O

minusC9H12O2 CH3

CH3

CH3

CH3

CH3

CH3

(OH)2

(OH)3

(OH)4

H3C

H3C

minusCH3OCH3

minusCH3OH

CH3

CH3

CH3

CH3

CH3

CH3

CH3

minusNH3

H3C

H3C

H3C

H2C

minusH2O

minusNH3

minusCH3OH

Figure 6 Proposed pathways for the degradation of MET

The integrated form of the above equation is represented by

ln(119862119900

119862) = 119896app sdot 119905 (6)

where 1198620is the initial pollutant concentration and 119896app is the

apparent pseudo-first-order reaction rate constantThe half-life was calculated with the following expression

11990512

=ln 2119896 (7)

The values of 11990512

in Table 2 verify that the direct photolysisunder simulated light was very low The low photodegra-dation of MET was also supported by a low molar absorp-tion coefficient (281 Lmolminus1 cmminus1) measured at 2219 nmwavelength However an important increasing difference isobserved in the MET degradation when TiO

2is present

Also when photocatalytic process is applied results inTOC conversion (63) are notoriously improved for initialconcentration of 50mg Lminus1 of MET and 04 g Lminus1 of catalyst

If both processes are compared photocatalytic processis always much faster than the photolytic degradation ofMET Therefore the interest of using photocatalysis in thetreatment of this type of pollutant is obvious

35 Intermediates during Reaction The major by-productsformed during 6 hours of photocatalytic treatment of MET

were identified (Figure 5) The study was carried out usingHPLCMS in positive electrospray model The degradationintermediates for MET are shown in Table 3

The metoprolol has a molecular weight [M + H+] = 268Three intermediates corresponding to the binding of ∙OHradicals in the aromatic ring were detected at 119898119911 300 316and 332 di-(DP (Detected Compound) 16) tri-(DP 17) andtetrahydroxy (DP 18) DPs respectively After breaking the CndashC bond in the aliphatic part of theMETmolecule amino-diol(DP 8) was identified as one of the dominant intermediateswith119898119911 = 134 Different fragments of the ethanolamine sidewere also identified (DP 1 DP 2 DP 3 DP 4 DP 5 DP 6 andDP 7) probably due to the loss of the hydroxyl group and theloss of isopropyl moiety

PD 15 can be formed probably by reactions which involveattack on the ether side chain followed by elimination Onthe other hand the oxidation of alcohols to aldehydes canbe explained by the formation of DP 14 with 119898119911 = 238[47] The hydrogen abstraction and the water eliminationof DP 14 probably generate a carbonyl followed by anintermolecular electron transfer it generates a double bondand the consequent formation of DP 12

Oxidative attack on the dimethylamine moiety resultsin a DP 13 with 119898119911 = 226 Following this the hydrogenabstraction and elimination of water of DP 13 generate acarbonyl which followed by intermolecular electron transfer-ence generates a double bond and forming DP 11 The DP

International Journal of Photoenergy 9

11 can generate DP 10 corresponding to a loss of ammoniaafter the hydrogen abstraction The intermediate 9 could beformed by the loss of methanol combined with the attack of∙OH on the C atom next to the ether oxygen in the aliphaticpart of DP 10

A simplified fragmentation pathway ofmetoprolol degra-dation is shown in Figure 6

4 Conclusions

Langmuir isotherm fits very well the experimental datawhich indicates that the adsorption of the MET onto TiO

2

is by monolayer coverage of the catalyst surface The resultsconfirmed that the degradation of MET is not able toundergo by direct photolysis due to its lower absorptioncoefficient In contrast the addition of TiO

2photocatalyst

significantly increases its degradation rate and after 240minof irradiation MET was totally eliminated for pH 9 Theexperimental data indicates that TiO

2photocatalysis allows

a fast and efficient removal of metoprolol transformingsubstrate into by-products that are more difficult to bedegraded by photocatalysis as evidenced by the level ofmineralization achieved (63) Disappearance of MET byphotocatalysis follows Langmuir-Hinshelwood model thatcan be simplified as a pseudo-first-order equation as usuallyfound in heterogenous photocatalysis at low concentrationPhotocatalytic degradation rate of MET depends on pHoccurring the faster degradation at pH 9 At last based onthe identified degradation intermediates at 6-hour reactiontime a photocatalytic degradation pathway ofmetoprolol wasproposed The main pathways involved in the photocatalyticdegradation process include hydroxilation of the aromaticring shortening of methoxyl contained in the lateral chainand cleavage of or addition of ∙OH to the amine lateral chain

Acknowledgments

The authors are grateful to CICYT Project CTQ2011-26258Consolider-Ingenio NOVEDAR 2010 CSD2007-00055 andAGAUR Generalitat de Catalunya (Project 200956R 1466)for funds received to carry out this work

References

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[2] Y Xu T V Nguyen M Reinhard and K Y-H GinldquoPhotodegradation kinetics of p-tert-octylphenol 4-tert-octylphenoxy-acetic acid and ibuprofen under simulated solarconditions in surface waterrdquo Chemosphere vol 85 no 5 pp790ndash796 2011

[3] A Jurado E Vazquez-Sune J Carrera M Lopez de Alda EPujades and D Barcelo ldquoEmerging organic contaminants ingroundwater in Spain a review of sources recent occurrenceand fate in a European contextrdquo Science of the Total Environ-ment vol 440 pp 82ndash94 2012

[4] M Huerta-Fontela M T Galceran and F Ventura ldquoOccur-rence and removal of pharmaceuticals and hormones throughdrinking water treatmentrdquo Water Research vol 45 no 3 pp1432ndash1442 2011

[5] M Pedrouzo F Borrull E Pocurull and R M Marce ldquoPres-ence of pharmaceuticals and hormones in waters from sewagetreatment plantsrdquoWater Air and Soil Pollution vol 217 no 1ndash4pp 267ndash281 2011

[6] A C Alder C Schaffner M Majewsky J Klasmeier and KFenner ldquoFate of 120573-blocker human pharmaceuticals in surfacewater comparison of measured and simulated concentrationsin theGlatt ValleyWatershed SwitzerlandrdquoWater Research vol44 no 3 pp 936ndash948 2010

[7] M Maurer B I Escher P Richle C Schaffner and A C AlderldquoElimination of 120573-blockers in sewage treatment plantsrdquo WaterResearch vol 41 no 7 pp 1614ndash1622 2007

[8] B Abramovic S Kler D Sojic M Lausevic T Radovic andD Vione ldquoPhotocatalytic degradation of metoprolol tartrate insuspensions of two TiO

2-based photocatalysts with different

surface area Identification of intermediates and proposal ofdegradation pathwaysrdquo Journal of HazardousMaterials vol 198pp 123ndash132 2011

[9] M Maurer B I Escher P Richle C Schaffner and A C AlderldquoElimination of 120573-blockers in sewage treatment plantsrdquo WaterResearch vol 41 no 7 pp 1614ndash1622 2007

[10] E Isarain-Chavez J A Garrido R M Rodrıguez et al ldquoMin-eralization of metoprolol by electro-fenton and photoelectro-fenton processesrdquo Journal of Physical Chemistry A vol 115 no7 pp 1234ndash1242 2011

[11] L Prieto-Rodrıguez I Oller N Klamerth A Aguera E MRodrıguez and S Malato ldquoApplication of solar AOPs andozonation for elimination of micropollutants in municipalwastewater treatment plant effluentsrdquo Water Research vol 47pp 1521ndash1528 2013

[12] I Kim and H Tanaka ldquoPhotodegradation characteristics ofPPCPs in water withUV treatmentrdquo Environment Internationalvol 35 no 5 pp 793ndash802 2009

[13] A Piram A Salvador C Verne B Herbreteau and R FaureldquoPhotolysis of 120573-blockers in environmental watersrdquo Chemo-sphere vol 73 no 8 pp 1265ndash1271 2008

[14] H Fang Y Gao G Li et al ldquoAdvanced oxidation kineticsand mechanism of preservative propylparaben degradationin aqueous suspension of TiO

2and risk assessment of its

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[15] L D Nghiem A I Schafer andM Elimelech ldquoPharmaceuticalretention mechanisms by nanofiltration membranesrdquo Environ-mental Science and Technology vol 39 no 19 pp 7698ndash77052005

[16] T Heberer ldquoOccurrence fate and removal of pharmaceuticalresidues in the aquatic environment a review of recent researchdatardquo Toxicology Letters vol 131 no 1-2 pp 5ndash17 2002

[17] C Hartig M Ernst and M Jekel ldquoMembrane filtration of twosulphonamides in tertiary effluents and subsequent adsorptionon activated carbonrdquo Water Research vol 35 no 16 pp 3998ndash4003 2001

[18] J Radjenovic M Petrovic F Ventura and D Barcelo ldquoRejec-tion of pharmaceuticals in nanofiltration and reverse osmosismembrane drinking water treatmentrdquo Water Research vol 42no 14 pp 3601ndash3610 2008

10 International Journal of Photoenergy

[19] P Westerhoff Y Yoon S Snyder and E Wert ldquoFate ofendocrine-disruptor pharmaceutical and personal care prod-uct chemicals during simulated drinking water treatment pro-cessesrdquoEnvironmental Science andTechnology vol 39 no 17 pp6649ndash6663 2005

[20] J Peuravuori and K Pihlaja ldquoPhototransformations of selectedpharmaceuticals under low-energy UVA-vis and powerfulUVB-UVA irradiations in aqueous solutions-the role of naturaldissolved organic chromophoric materialrdquo Analytical and Bio-analytical Chemistry vol 394 no 6 pp 1621ndash1636 2009

[21] Q-T Liu R I Cumming and A D Sharpe ldquoPhoto-inducedenvironmental depletion processes of 120573-blockers in riverwatersrdquo Photochemical and Photobiological Sciences vol 8 no6 pp 768ndash777 2009

[22] Q-T Liu R I Cumming and A D Sharpe ldquoPhoto-inducedenvironmental depletion processes of 120573-blockers in riverwatersrdquo Photochemical and Photobiological Sciences vol 8 no6 pp 768ndash777 2009

[23] R Molinari F Pirillo V Loddo and L Palmisano ldquoHeteroge-neous photocatalytic degradation of pharmaceuticals in waterby using polycrystalline TiO

2and a nanofiltration membrane

reactorrdquo Catalysis Today vol 118 no 1-2 pp 205ndash213 2006[24] W Song W J Cooper S P Mezyk J Greaves and B M Peake

ldquoFree radical destruction of 120573-blockers in aqueous solutionrdquoEnvironmental Science and Technology vol 42 no 4 pp 1256ndash1261 2008

[25] M Janus J Choina and A W Morawski ldquoAzo dyes decom-position on new nitrogen-modified anatase TiO

2with high

adsorptivityrdquo Journal of Hazardous Materials vol 166 no 1 pp1ndash5 2009

[26] T E Doll and F H Frimmel ldquoFate of pharmaceuticalsmdashphotodegradation by simulated solar UV-lightrdquo Chemospherevol 52 no 10 pp 1757ndash1769 2003

[27] M Scepanovic B Abramovic A Golubovic et al ldquoPhotocat-alytic degradation of metoprolol in water suspension of TiO

2

nanopowders prepared using sol-gel routerdquo Journal of Sol-GelScience and Technology vol 61 pp 390ndash402 2012

[28] K L Willett and R A Hites ldquoChemical actinometry using o-Nitrobenzaldehyde to measure light intensity in photochemicalexperimentsrdquo Journal of Chemical Education vol 77 no 7 pp900ndash902 2000

[29] N De la Cruz V Romero R F Dantas et al ldquoo-Nitrobenzaldehyde actinometry in the presence of suspendedTiO2for photocatalytic reactorsrdquo Catalysis Today vol 209 pp

209ndash214 2013[30] F J Rivas O Gimeno T Borralho and M Carbajo ldquoUV-C

radiation based methods for aqueous metoprolol eliminationrdquoJournal of Hazardous Materials vol 179 no 1ndash3 pp 357ndash3622010

[31] D Fatta-Kassinos M I Vasquez and K Kummerer ldquoTrans-formation products of pharmaceuticals in surface waters andwastewater formed during photolysis and advanced oxidationprocesses - Degradation elucidation of byproducts and assess-ment of their biological potencyrdquo Chemosphere vol 85 no 5pp 693ndash709 2011

[32] S Sortino S Petralia F Bosca and M A Miranda ldquoIrre-versible photo-oxidation of propranolol triggered by self-photogenerated singlet molecular oxygenrdquo Photochemical andPhotobiological Sciences vol 1 no 2 pp 136ndash140 2002

[33] Q-T Liu and H E Williams ldquoKinetics and degradation prod-ucts for direct photolysis of 120573-blockers in waterrdquo EnvironmentalScience and Technology vol 41 no 3 pp 803ndash810 2007

[34] P Fernandez-Ibanez F J De Las Nieves and S Malato ldquoTita-nium dioxideelectrolyte solution interface electron transferphenomenardquo Journal of Colloid and Interface Science vol 227no 2 pp 510ndash516 2000

[35] A Mills and S Le Hunte ldquoAn overview of semiconductorphotocatalysisrdquo Journal of Photochemistry and Photobiology Avol 108 no 1 pp 1ndash35 1997

[36] F J Benitez J L Acero F J Real G Roldan and F CasasldquoBromination of selected pharmaceuticals in water matricesrdquoChemosphere vol 85 no 9 pp 1430ndash1437 2011

[37] K Y Foo and B H Hameed ldquoInsights into the modeling ofadsorption isotherm systemsrdquo Chemical Engineering Journalvol 156 no 1 pp 2ndash10 2010

[38] K V Kumar and K Porkodi ldquoRelation between some two- andthree-parameter isothermmodels for the sorption ofmethyleneblue onto lemon peelrdquo Journal of Hazardous Materials vol 138no 3 pp 633ndash635 2006

[39] J S Piccin G L Dotto and L A A Pinto ldquoAdsorptionisotherms and thermochemical data of FDandC RED N∘ 40Binding by chitosanrdquoBrazilian Journal of Chemical Engineeringvol 28 no 2 pp 295ndash304 2011

[40] F Mendez-Arriaga J Gimenez and S Esplugas ldquoPhotolysisand TiO

2photocatalytic treatment of naproxen degradation

mineralization intermediates and toxicityrdquo Journal of AdvancedOxidation Technologies vol 11 no 3 pp 435ndash444 2008

[41] V Romero N de La Cruz R F Dantas P Marco J Gimenezand S Esplugas ldquoPhotocatalytic treatment of metoprolol andpropranololrdquo Catalysis Today vol 161 no 1 pp 115ndash120 2011

[42] L A Ioannou E Hapeshi M I Vasquez D Mantzavinos andD Fatta-Kassinos ldquoSolarTiO

2photocatalytic decomposition of

120573-blockers atenolol and propranolol in water and wastewaterrdquoSolar Energy vol 85 no 9 pp 1915ndash1926 2011

[43] FMendez-Arriaga S Esplugas and J Gimenez ldquoPhotocatalyticdegradation of non-steroidal anti-inflammatory drugs withTiO2and simulated solar irradiationrdquo Water Research vol 42

no 3 pp 585ndash594 2008[44] H Yang T An G Li et al ldquoPhotocatalytic degradation kinetics

and mechanism of environmental pharmaceuticals in aqueoussuspension of TiO

2 a case of 120573-blockersrdquo Journal of Hazardous

Materials vol 179 no 1ndash3 pp 834ndash839 2010[45] R F Dantas O Rossiter A K R Teixeira A S M Simoes

and V L da Silva ldquoDirect UV photolysis of propranololand metronidazole in aqueous solutionrdquo Chemical EngineeringJournal vol 158 no 2 pp 143ndash147 2010

[46] C Sahoo A K Gupta and I M S Pillai ldquoHeterogeneousphotocatalysis of real textile wastewater evaluation of reactionkinetics and characterizationrdquo Journal of environmental scienceand health A vol 47 pp 2109ndash2119 2012

[47] M L Wilde W M M Mahmoud K Kummerer and A FMartins ldquoOxidation-coagulation of 120573-blockers by K2FeVIO4in hospital wastewater assessment of degradation products andbiodegradabilityrdquo Science of the Total Environment vol 452-453pp 137ndash147 2013

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Carbohydrate Chemistry

International Journal of

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Journal of

Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Advances in

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Analytical Methods in Chemistry

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Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of

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Medicinal ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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Analytical ChemistryInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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