-
loe i
Sheng Deng a, Guangshan Zhang a, Xi Wang a, Tong Zheng a, Peng
Wang a,b,a School of Municipal and Environmental Engineering, Hb
State Key Laboratory of Urban Water Resource and En
iation oard Cuiation s
ns, were investigated strictly and the experimental data tted
the Langmuir
ulation and industrialization in the world, the frequency of
acci-dently heavy metal pollution boosted fast in recent years. Due
toits non-biodegradation and non-decomposing characters, metalions
can be accumulated through food chain and then absorbedby
human-being [2]. Mercury is one of the most toxic metal
ions,especially when the metal is transferred into methyl mercury
by
. Mostly, mercuryr disposal of cer-uorescents. When itage,
brain
ciency and liver disfunction may be caused [3]. Meanwhile,has
also been widely used in electrical engineering, macmanufactory and
construction industry, leading to the risk of sev-ere
gastrointestinal irritation, muscular pain and possible
necroticchange in kidney [4]. Thus, how to remove heavy metal ions
fromwater environment has become a vital study, especially when
sud-den pollution accident happens.
Many techniques, including solvent extraction, membrane
sep-aration, electrochemical operation, adsorption, and ion
exchange,
Corresponding author. Tel./fax: +86 451 86283557.E-mail address:
[email protected] (P. Wang).
Chemical Engineering Journal 276 (2015) 349357
Contents lists availab
ne
w.1. Introduction
Heavy metal ions are highly toxic to human health, and the
dis-charge to environment was mainly caused by
anthropogenicbehavior and nature disaster [1]. With the rapid
growth of pop-
anaerobic organism in the aqueous environmentcan enter into the
environment through impropetain products including auto parts,
batteries, medical products, thermometers and thermostatinto human
body, central nervous system
damhttp://dx.doi.org/10.1016/j.cej.2015.04.0431385-8947/ 2015
Elsevier B.V. All rights
reserved.bulbs,comesinef-copperhineryKeywords:Microwave
irradiationPolyacrylonitrile berAdsorptionCopperMercuryNon-thermal
effect
model (R2 > 0.99) and pseudo-second-order equation very well.
The effect of pH on the adsorption capac-ity of metal ions was
discussed and the optimal value for Cu(II) and Hg(II) was found to
be 5.0 and 2.0,respectively. Thermodynamic parameters reveal the
spontaneous and endothermic nature of the adsorp-tion process, due
to the negative value of standard free energy (DG) and the positive
value of standardenthalpy (DH). The adsorption capacities toward
Cu(II) and Hg(II) on the modied polyacrylonitrile bersunder
microwave irradiation are higher than those on other adsorbents
through conventional heating.The less consumed time and high
grafting rate of the functional groups may be attributed to
thermaleffect as well as non-thermal effect of microwave
irradiation.
2015 Elsevier B.V. All rights reserved.tal analysis (EA),
scanningnamic and kinetic conditioh i g h l i g h t s
Modied bers under microwave irrad The maximum adsorption
capacity tow Non-thermal effect of microwave irrad
a r t i c l e i n f o
Article history:Received 21 February 2015Received in revised
form 7 April 2015Accepted 8 April 2015Available online 15 April
2015arbin Institute of Technology, Harbin 150090, PR
Chinavironment, Harbin Institute of Technology, Harbin 150090, PR
China
wns higher adsorption capacity.(II) and Hg(II) was 119.39 and
275.76 mg g1.howed same impact with thermal effect.
a b s t r a c t
Polyacrylonitrile ber immobilized with iminodiacetic acid (IDA)
was prepared under microwave irradia-tion and was used to adsorb
Cu(II) and Hg(II) in aqueous solution. Synthesis conditions such as
time, tem-perature and ratio of solvents were exploited
systematically by orthogonal experiment and the propertiesof this
brous absorbent were characterized by fourier transform infrared
spectroscopy (FT-IR), elemen-
electron microscopy (SEM). The adsorption performances, in both
thermody-of Cu(II) and Hg(II)Preparation and performance of
polyacrywith iminodiacetic acid under microwav
Chemical Engi
journal homepage: wwnitrile ber functionalizedrradiation for
adsorption
le at ScienceDirect
ering Journal
elsevier .com/locate /cej
-
have been utilized to fulll the task [5]. Among these
methods,adsorption is expected to be an attractive way due to its
removalefciency as well as excellent reusability. Activated carbon
[6],oxide minerals [7], polymer materials [8], resins [9] and
biosor-bents [10] have been applied as absorbents to extract metal
ionsfrom the aqueous solution. The efciency of the absorption
processdepends on the capability of the absorbents, where
immobilizedfunctional groups play a dominant role in it. It is
widely acknowl-edged that chelating agents such as IDA exhibit good
afnity withmetal ions. IDA is a typical type of aminopolycarboxylic
acids thatcontains two carboxyl groups bound to one nitrogen atom.
Thehigh adsorption capacity of IDA absorbents may attributes to
theformation of stable metal-IDA chelates with multidentate
interac-tion. Based on different raw materials such as silica gel,
chitosan,acrylonitrile-divinylbenzene (AN-DVB) and amino methyl
poly-styrene (AMPS), many IDA functionalized absorbents were
suc-cessfully invented in recent years [1113]. The chelating
brousadsorbents have attracted considerable attention owing to
theirlarge specic surface area and quick mass transfer velocity. At
pre-sent, many researchers have explored the synthesis and
modica-tion of various chelating ber absorbents in an effort to
enhancethe afnity of metal ions [14,15]. However, most of these
methods
to its advantage of high-efciency, selectively heating and no
pol-lution to environment, MW has been widely used in various
elds,such as food processing, pharmaceutical synthesis and organic
syn-thesis reaction [1719]. Our group has done some researches
onthe application of MW and many achievements have beenobtained
[2024].
In the study, an IDA modied chelating ber based on
polyacry-lonitrile was synthesized in two steps through MW
irradiation. Thereaction parameters such as time, temperature and
ratio of sol-vents were optimized thoroughly. The adsorption
performance ofCu(II) and Hg(II) onto the IDA functionalized ber was
studied.The effect of various parameters including pH, initial
concentra-tion, contact time and temperature on the adsorption
process weredeeply investigated. In addition, the equilibrium
isotherms, kineticmodels and thermodynamic parameters were utilized
and calcu-lated for the adsorption of Cu(II) and Hg(II) on the
modied ber.
2. Experimental
2.1. Materials
The polyacrylonitrile ber (PANF) made by 100% acrylonitrile
350 S. Deng et al. / Chemical Engineering Journal 276 (2015)
349357are accomplished by using conventional heating such as
water-bath heating, oil-bath heating and electrical heating ask,
whichare low efciency, high energy waste and low safety.
Radiationinduced or electron-beam-induced technique is less
universalowing to its high price and unstability.
Microwave (MW) is electromagnetic waves with wavelengthsbetween
1 mm and 1 m (frequencies of 300 GHz to 300 MHz).Contrasted with
heat-transfer way of conventional heating, MWirradiation can make
dipolar molecules rotate and ions migratewhen penetrate into
samples, then cause heating throughout thevolume of the product.
The most commonmechanism of MW heat-ing is dipolar polarization
which means a dipolar molecule such aswater tries to align itself
within the electric eld of MW, and heat-ing was caused by
frictional resistance of molecular rotation. Thismechanism is
utilized in the domestic MW oven where water actsas the MW
receptor. In addition, the non-thermal effects were alsobelieved to
affect the reaction in some degree [16]. By using thisrapid in core
volumetric heating, heating time can be up to threeorders of
magnitude lower than that of conventional heating. DueScheme 1. The
synthetic swas purchased from Beijing Rongnai industry material
company.Diethylenetriamine, anhydrous ethanol, chloroacetate acid,
andsodium bicarbonate were all supplied by Aladdin Corporation
ofChina. The solution of Cu2+ and Hg2+ ions were prepared by
dissolv-ing weighted amounts of copper and mercury nitrates
(SinopharmChemical Reagent Co. Ltd) in deionized water.
2.2. Microwave-assisted preparation of polyacrylonitrile ber
modiedby IDA
The PANF was dried in the oven overnight before use and cutinto
5 cm length, so that it wont get twined while stirring.
Thesynthetic reaction was carried out as in the following two
stepsand shown in Scheme 1.
(1) The PAN ber was initially modied via amination reaction.An
orthogonal experiment design, described in Table 1, wasapplied to
conduct this synthetic procedure. In a typical syn-thesis, 1.0 g
PANF, diethylenetriamine (DETA), and deionizedcheme of
PANMW-IDA.
-
water were added into a 250 mL three neckask and thesolution was
ultrasonicated for 5 min, followed by the addi-tion of some
zeolites. The ask was moved into the MWreactor (COOLPEX-E with
output power 1200W, purchasedfrom PreeKem Scientic Instruments Co.,
Ltd., China) andthe parameters of time and temperature were set up.
Fig. 1shows the components of the MW reactor. As the volumeof the
mixed solution was less than 100 mL, all experimentswere conducted
at PMW = 500W according to the instructionof MW reactor.
The reaction was carried out under continuous stirring. Afterit
was nished, the mixture was cooled till room tempera-ture. Then the
ber was ltered, washed with anhydrousethanol and hot deionized
water until neutral. Finally, theproduct was dried in a vacuum oven
at 343 K overnight.
The grafting percentage (GP) was calculated by gravimetrythrough
following equation:
GP m1 m0m0
100% 1
where m0 and m1 are the weights of raw polyacrylonitrileber and
amine grafted ber, respectively. The grafted PANber was named as
PANMW-DETA.
(2) The IDA modied ber was prepared by the action of
abovePANMW-DETA ber with 100 mL chloroacetate acid (CAA).The pH of
the solution was then adjusted to 89 by addingsaturated sodium
bicarbonate. The reaction was carriedout at 378 K in the MW reactor
for 15 min. After the reactionnished, the mixture was cooled at
room temperature. Theber was ltered and washed with anhydrous
ethanol andhot deionized water until neutral. Then the chelating
berwas dried in vacuum at 343 K overnight. The obtained berwas
named as PANMW-IDA.
2.3. Characterization of PANMW-IDA
FT-IR spectra was scanned in the region of 4004000 cm1 inKBR
pellets on PerkinElmer spectrum. The PAN and modiedbers were dried
overnight at 343 K in vacuum oven.
Table 1Investigated variables and their levels.
Levels ofeach variables
A B CWater/diethylenetriamineratio (V/V)
Temperature(K)
Time(min)
1 1:2 383 102 1:1 388 203 2:1 393 30
S. Deng et al. / Chemical Engineering Journal 276 (2015) 349357
351Fig. 1. The chart of the MW reactor (PreeKem Scientic
Instruments Co., Ltd.).
-
strongly with microwave can lead to much higher heating
ratesthan those which are achieved conventionally. The magnitude
ofheating depends on the dielectric properties of the
molecules[25,26]. The dielectric constant of water and DETA is 81.5
and 4.1at 23 C, respectively, which makes both of them suitable for
thereaction under MW irradiation. The ratio of solutions,
temperatureand reaction time affect both the amination rate of bers
and themechanical strength. Theoretically, raised temperature
andextended reaction time lead to high grafting rate, but the
mechani-cal strength of ber dropped largely at the same time. So
theorthogonal experiments were conducted to optimize the
bestcondition.
The orthogonal results show that the main inuence factor istime
and the inuence order of different parameters is: C > B >
A,by evaluating the K(k) values of each factor listed in Table 2.
Theoptimum combination program was A2B3C3, in
detail:V(water):V(DETA) = 1:1; temperature at 120 C, reaction time
for30 min. In order to prove the optimized result with the
largest
ering Journal 276 (2015) 349357The elemental analysis (EA) of
PAN, PANMW-DETA andPANMW-IDA ber was obtained from a Perkin-Elmer
240 CElemental Analytical Instrument (Germany).
The surface morphologies of the raw and modied bers wereexamined
at FEI Quanta-200 scanning electron microscope (FEICompany, The
Netherlands). The samples were sputter-coatedwith gold for 40s at
15 mA prior to the SEM observation.
2.4. Adsorption experiments
The adsorption properties of PANMW-IDA toward Cu(II) andHg(II)
were determined under non-competitive conditions by add-ing the ber
into a solution containing each one metal ion.
2.4.1. Effect of pHThe capacity of the chelating ber was
affected by the pH of the
metal solution in a certain range. In order to determine the
effect ofpH, 0.100 g PANMW-IDA ber was added into a series of 100
mL(300 mg L1) of metal ion solution with different pH values(16).
The mixture was shaken in thermostatic water bath for24 h at 293 K.
Then the solution samples were taken out by syringeand ltered with
a 0.45 lm membrane to remove tiny ber frag-ments. These ltrates
were used to measure the nal concentrationof metal ions by
ultravioletvisible spectroscopy (UVVIS) andinductively coupled
plasma atomic emission spectroscopy (ICP-AES). This procedure was
repeated for three times, and the averageof results was obtained.
The amount of the metal ions adsorbedonto the chelating ber (q, mg
g1) was calculated on the basis ofthe following equation:
q C0 CeVm
2
where C0 and Ce are the initial and the equilibrium
concentration ofthe metal ions in the test solution (mg L1),
respectively, V is thevolume of the testing solution (L), and m is
the weight of the adsor-bent (g).
2.4.2. Adsorption kineticsIn kinetic adsorption experiments, an
amount of 0.100 g of
PANMW-IDA ber was added into the 100 mL of metal ion
solution(300 mg L1) where the initial pH of the solution was
adjusted to5.0 and 2.0 for Cu(II) and Hg(II), respectively. The
solution sampleswere agitated at thermostatic water bath at 293 K
and draw out atregular intervals from 5 min to 240 min. The
solutions were l-tered with a 0.45 lm membrane and the remaining
amounts ofmetal ions were determined by UVVIS and ICP-AES.
2.4.3. Adsorption isothermsEquilibrium adsorption of Cu(II) and
Hg(II) were conducted as
follows: 0.100 g amount of PANMW-IDA ber was introduced into250
mL asks respectively, and then 100 mL aqueous solutionswith
different concentrations of certain metal ion were added intothose
asks. Then the asks were completely sealed and placed in aSHA-C
model thermostatic water bath oscillator at different tem-peratures
(283 K, 293 K, 303 K). The batch test ran continuouslyfor 24 h to
ensure that the adsorption equilibrium has beenreached and the
concentrations of heavy metal ions weredetermined.
3. Results and discussion
3.1. Preparation of PANMW-IDA ber under MW irradiation
352 S. Deng et al. / Chemical EngineThe introduction of
microwave energy into a chemical reactionwhich has at least one
component that is capable of couplingweight gain in Table 2,
adsorption tests using PANMW-DETA wereperformed three times. The
results show that the optimum com-bination programwas A2B3C3 with
the highest adsorption capacity.Compared to previous brous
adsorbent studies [27,28], the tem-perature raised 1030 C under MW
irradiation while the berwould melt if conventional heating was
applied in this condition.The non-thermal effect of MW may
attribute to the high graftingrate in terms of a short duration of
this process.
The parameters inuenced the formation of IDA functionalgroup
such as temperature, time were also discussed. The resultsrevealed
that when temperature was higher than 105 C, the syn-thesized ber
was easily fractured while the weight gain increasedslightly. This
may be caused by the effects of strong alkalinesolution and high
energy of MW irradiation. Same results wereobtained when time
increased more than 15 min. So in this step,temperature and time
were controlled at 105C and 15 min,respectively. Under this
condition, 2025% weight gainPANMW-IDA ber was fabricated.
3.2. Characterization of PANMW-IDA
The FT-IR spectra of (a) PANF, (b) PANMW-DETA and (c)PANMW-IDA
were presented in Fig. 2. A sharp and distinct adsorp-tion band at
2243 cm1 in PANF, PANMW-DETA, PANMW-IDAattributed to CN group in
the polyacrylonitrile ber. Althoughthe ber was claimed to be made
of 100% acrylonitrile, the
Table 2Orthogonal experimental arrangement and test result.
Experimentalnumber
Factors GP (%)
A B C
1 1:2 383 10 3.02 1:2 388 20 5.43 1:2 393 30 174 1:1 383 20 8.25
1:1 388 30 406 1:1 393 10 137 2:1 383 30 138 2:1 388 10 129 2:1 393
20 34K1 25.4 24.6 27.8K2 61.0 57.4 47.6K3 59.4 63.8 70.4k1 8.47
8.20 9.27k2 20.3 19.1 15.9k3 19.8 21.3 23.5R 11.8 13.1 14.2
Order C > B > AOptimal condition A2B3C3
-
obviously. Compared with PANF, PANMW-IDA showed an observed
S. Deng et al. / Chemical Engineering Journal 276 (2015) 349357
353Fig. 2. FT-IR spectra of (a) PANF, (b) PANMW-DETA and (c)
PANMW-IDA.
Table 3The dates of element analysis of PAN, PANMW-DETA and
PANMW-IDA.
Sample Element content (%) C/N(mole ratio)
C/O(mole ratio)
C N O
PAN 65.48 26.52 2.59 2.88 25.21PANMW-DETA 56.39 23.94 12.82 2.75
4.4PANMW-IDA 51.43 18.78 23.61 3.2 2.18adsorption peak at 1731 cm1
still conrmed the existence ofmethyl acrylate. After DETA was
attached onto the ber, theadsorption intensity of both CN group and
methyl acrylatedecreased but not omitted, and new peaks appeared at
1665 and1600 cm1 corresponding to the banding vibration of NH2
groupand the stretching vibration band of C@O group [29],
whichsuggests the CN group was hydrolyzed into O@COH
initiallybefore it further reacted with DETA (Fig. 2b). A broad
peak at16841543 cm1 occured after functionalized by CAA,
whichattributed to C@O stretching vibration of carboxylic and
carboxylategroups (Fig. 2c). The board adsorption band at 34003100
cm1
corresponds to the combination of NH and O@COH groups
[30,31].The results of the elemental analysis of C, N, O of the
bers were
given in Table 3. The C value of PANMW-DETA and
PANMW-IDAdecreased after the grafting and modication, which mainly
attri-bute to the lower carbon content of DETA and CAA. Due to
thehydrolysis of CN group into O@COH, the N value decline wasfound
in PANMW-DETA which coordinates to the result of FT-IR.Higher
oxygen content was observed in PANMW-IDA, indicates
Fig. 3. SEM characterization of (a) PANF, (increase in diameter
whichmay be due to the insertion of the DETAchains onto the PAN ber
surface and the conversion of aminegroups into IDA groups in
grafted chains [32]. As the reactionproceeded, the ber swelled up
and its color changed from faintyellow to brown yellow. Therefore,
the introduction of amine,amino and carboxyl groups was expected to
change the propertiesof the original ber and then affect metal ion
adsorption.
3.3. Adsorption performance of PANMW-IDA
3.3.1. Effect of pHThe pH of the adsorbate solution not only
affects metal species
in solution, but also inuences the surface properties of the
adsor-bents in terms of dissociation of functional groups and
surfacecharges. For that, the adsorption of Cu(II) and Hg(II) were
studiedin the range of 16, and Fig. 4 shows the uptake of the metal
ionshas nearly no crack. After modication, the PANMW-IDA becamevery
rough and the crack on the surface of PANMW-IDA increasedthe
carbonyl was successfully attached in the ber. EA and FT-IRspectrum
results proved that the IDA functional group has beenimmobilized in
PANF.
The morphologies of (a) PANF, (b) PANMW-DETA and (c)PANMW-IDA
were observed by SEM and the results were shownin Fig. 3. It can be
seen that the surface of PANF is smooth and
Fig. 4. Effect of pH on the adsorption capacity of PANMW-IDA for
Cu2+ and Hg2+ at293 K.with an initial concentration of 300 mg L1.
It is seen that theadsorption of copper ascended when the pH
increased from 1.0to 5.0. This phenomenon can be attributed to the
protonation ofthe active groups and the competition of H+ with
metal ions onadsorption sites [33]. Similar result was obtained for
mercurywhen the pH increased from 1.0 to 2.0. However, as the
pH
b) PANMW-DETA and (c) PANMW-IDA.
-
has reached half saturated in less than 20 min and nearly
saturated The calculated kinetics parameters for adsorption of
Cu(II) andHg(II) onto the modied ber were tabulated in Table 4. As
canbe observed, the pseudo-second-order equation, correlation
coef-cient (R2) of Cu(II) and Hg(II) are both 0.999, appeared to be
thebetter tting model than the pseudo-rst-order.
Pseudo-rst-orderbelieves that the mass transfer resistance is the
restriction factor ofadsorption, while pseudo-second-order
considers that the adsorp-tion mechanism affects instead [39]. The
adsorption of the metalsions onto the chelating ber is controlled
by chemisorptionthrough chelation interaction, coordinated to the
result of
Fig. 6. Adsorption isotherm of metal ions on PANMW-IDA at 283 K,
293 K and 303 K.
354 S. Deng et al. / Chemical Engineering Journal 276 (2015)
349357in 2 h toward both Cu(II) and Hg(II), indicating that the
modiedber has a rapid capture ability at metal ions. At the initial
stage,the fast rate of adsorption was mainly due to the high
collisionpossibility with chelate groups which was controlled by
the diffu-sion and migration process of metal ions in the solution
to theactive site on the surface of functionalized ber [38]. As
time wenton, the concentration of Cu(II) and the active site
decreased and theadsorption rate slowed down.
Lagrange kinetic models were used to describe the
mechanismcontinued to increase, the adsorption shows substantial
descend-ing, which is probably due to the formation of Cu(OH)2
andHg(OH)2 [34]. Our results in this study are consistent with
theobservation of Jie chen et al. [35] and Zhang yu et al.
[36].Furthermore, it should be noted that PANMW-IDA showed a
relativehigh adsorption capacity for Hg(II) even under strong
acidic condi-tion (pH = 2.0), which could be signicant for Hg(II)
recovery fromstrong acidic aquatic system like mining efuents
[37].
3.3.2. Effect of contact time and adsorption kineticsThe
time-dependent adsorption performances of PANMW-IDA
were investigated to determine the capacity with two metal
ions.Fig. 5 showed the adsorption kinetic curves of PANF
andPANMW-IDA of two metal ions at optimum pH. The chelating ber
Fig. 5. Adsorption kinetics of Cu2+ and Hg2+ at 293 K.of
adsorption process. The equation of pseudo-rst-order
andpseudo-second-order can be written as follows:
lnqe qt lnqe k1 3
tqt 1k2q2e
tqe
4
where qe and qt are the amounts of metal ions adsorbed on
theadsorbent (mg g1) at equilibrium and at time t, respectively;
k1and k2 are the rate constant of the rst-order adsorption in
min1
and the second-order adsorption in (g mg1 min1),
respectively.
Table 4Kinetic parameters for the adsorption of Cu2+ and
Hg2+.
Metal Pseudo-rst-order model
k1(min1)
qe(mg g1)
R2
Cu2+ 0.018 55.84 0.9724Hg2+ 0.023 128.32
0.9846pseudo-second-order.
3.3.3. Adsorption isothermsThe adsorption behavior of the
chelating ber at different tem-
perature was investigated. As can be observed in Fig. 6, the
equilib-rium adsorption uptake of the PANMW-IDA increased
withincreasing the initial concentration of heavy metal ions and
theadsorption capacity of PANMW-IDA increased with increasing
tem-perature, indicating that the adsorption was an endothermic
pro-cess. Langmuir and Freundlich adsorption isotherm models
werewidely used to describe the adsorption progress
[40].TheLangmuir and Freundlich equations can be written as
follows:
Pseudo-second-order model
k2(103 g mg1 min1)
qe(mg g1)
R2
0.697 114.56 0.99910.29 258.37 0.9992
-
qe qmK lCe1 K lCe 5
increased randomness at the solidliquid interface, which
demon-strated that the adsorption process was favorable at higher
tem-perature and that the spontaneity of adsorption was
aconsequence of the increase in entropy. It is assumed that
adsorp-tion heats between 20.9 and 418.4 kJ mol1 are the heats of
chemi-cal reactions which represents the chemical adsorption
process[36,43]. The DH value for Cu(II) and Hg(II) are 21.48
and20.06 kJ mol1, respectively, suggesting that the adsorption of
thetwo metal ion on the PANMW-IDA ber was mainly chemicallyreactive
adsorption.
Table 5Thermodynamic parameters for the adsorption of Cu2+ and
Hg2+ on PANMW-IDA.
Metal ions DH(kJ mol1)
DS(Jmol1 k)
DG (kJ mol1)
283 K 293 K 303 K
Cu2+ 21.48 89 3.58 4.47 5.35Hg2+ 20.06 72 0.34 1.06 1.78
r ID
S. Deng et al. / Chemical Engineering Journal 276 (2015) 349357
355qe K fC1ne 6
where qe is the amount of metal ion adsorbed at equilibrium by
theadsorbent (mg g1), Ce is the equilibrium concentration (mg L1),
qmis theoretical saturation adsorption capacity (mg g1), Kl is the
equi-librium Langmuir constant, Kf and n are constants representing
theadsorption capacity and intensity of adsorption.
As presented, the equilibrium data of both Cu(II) and Hg(II)
ionswere well described by Langmuir isotherm model (R2 >
0.99)compared with Freundlich isotherm model. This indicated
thepresence of monolayer sorption phenomenon for copper and
mer-cury ions sorption by the PANMW-IDA adsorbent. The
monolayersaturation adsorption values were 119.39 and 275.76 mg g1
forCu(II) and Hg(II) ions (293 K), which are well agreed with
theexperimentally obtained values, respectively. As shown in Fig.
6,the maximum uptake on PANMW-IDA notes the order of Cu(1.88 mmol
g1) > Hg (1.37 mmol g1), while the surface of theber is
predominantly positive at this pH range, which meansthe chelation
force favor the interaction between adsorbent andmetal ions instead
of Coulombic forces [9,41,42].
3.3.4. Adsorption thermodynamics parametersThe thermodynamic
qualities such as Gibbs free energy change
(DG), entropy (DH) and enthalpy (DS) for the adsorption of
copperand mercury ions using PANMW-IDA bers were determined by
thefollowing equations:
DG RTLnk 7
Lnk DSR DH
RT8
where K is the adsorption equilibrium constant, R is the
universalgas constant (8.314 J mol1 K1), T is the temperature (K).
The val-ues of DH and DS could be obtained as the slope and
intercept froma linear plot between Lnk versus 1/T.
The obtained thermodynamic parameters for the adsorptionprocess
are given in Table 5. The negative values of DG indicatedthe
spontaneous behavior of the adsorption process, and the posi-tive
values ofDH andDS for the adsorption of Cu(II) and Hg(II)
sug-gested the endothermic behavior of this process, couple with
an
Table 6Comparison PANMW-IDA ber adsorption capacities with
otheAdsorbents Reaction ti(h)
Glycidyl methacrylate Silica gel 18Fe3O4-glycidyl
methacrylate-iminodiacetic
acid-styrene-divinyl benzene resin12
Polybenzylamine 30Amino methyl polystyrene 22Nature wool ber
5Buckwheat hulls PANMW-IDA ber 0.753.4. Comparison between
PANMW-IDA and other adsorbents
The comparison of PANMW-IDA ber synthesized through
MWirradiation with various IDA functionalized adsorbents
fabricatedunder conventional heating in terms of time and
adsorptioncapacities for Cu(II) and Hg(II) is given in Table 6.
The duration of functionalization process decreased remarkablyby
using microwave irradiation compare to conventional heatingmethod,
more specically, the consumed time declined from5-30 h to 0.75 h.
Although PANMW-IDA ber has lower adsorptioncapacity for Cu(II) than
IDA modied amino methyl polystyrene,it has a comparative adsorption
capacity of copper ion with otherIDA modied adsorbents, as well as
a much better binding abilitytoward mercury ion. The higher
capacity may attribute to the hightransferring rate of cyano group
to amine group and then takeeffects in the adsorption process.
The effect of microwave irradiation in chemical reactions is
acombination of the thermal effect and non-thermal effect.Thermal
effects were initiated by transforming electromagneticenergy to
heat, which is contract to conduction and convectionprocesses
observed in conventional heating. In particularly, thehigh yield of
PANMW-DETA was proved by experiments owing tothe ability of water
to transmit energy by dielectric losses. Theexperimental results
show that almost no grafting rate wasobserved if DETA was applied
as solvent solely.
In the meanwhile, the non-thermal effects, especially
overheat-ing make considerable differences in these two synthesis
processcompared to previous researches. Nearly all brous
adsorbentswere fabricated under 373 K in former studies, which is
the boilingpoint of water, for sake of maintaining its
crystallinity in such along period. While in this study, as the
consequence of the muchshorter interval of the reaction,
temperature is higher than theboiling point of water which cause
overheating effect in the solu-tion and then accelerate the
reaction process spectacularly.
4. Conclusions
The IDA group was rapidly grafted onto polyacrylonitrile berby
using MW irradiation through two-step modication: amina-tion and
carboxymethylation. Compared to conventional heating,MW irradiation
exhibits excellent advances such as high grafting
A functionalized adsorbents.
me Adsorption capacity(mg g1)
Reference
Cu2+ Hg2+
27.32 [44]78.17 [45]55.92 [46]
109.31 [47]144.25 [42]110.49 154.32 [48]
116.34 [49]119.39 275.76 Present study
-
erinrate and spectacularly acceleration of reaction process due
to thecombination of thermal effect and non-thermal effect.
Throughthe orthogonal experiment, the optimal conditions for the
maxi-mum rate of amination were found at V(water):V(DETA) =
1:1,temperature at 120 C and reaction time for 30 min. FT-IR
spectrawere used to conrm the formation of IDA group onto the
bers.At the optimum pH condition, the PANMW-IDA exhibited
highefciency of Cu(II) and Hg(II) capacity. The adsorption
kineticwas explained by Pseudo-second-order equation, which
wasproved to be chemical reaction. The adsorption followed
theLangmuir isotherm, indicating that the binding process took
placeat monolayer within the adsorbent, and the calculation
resultsabout DG, DH and DS indicated that the process was
spontaneousand endothermic. The adsorption of both Cu(II) and
Hg(II) metalsonto the PANMW-IDA are higher than those IDA
adsorbents inprevious studies.
Acknowledgments
The work was supported by State Key Laboratory of UrbanWater
Resource and Environment (Harbin Institute ofTechnology) (2015D03)
and the National Water Pollution Controland Management Technology
Major Projects (2012ZX07205-005).
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357
Preparation and performance of polyacrylonitrile fiber
functionalized with iminodiacetic acid under microwave irradiation
for adsorption of Cu(II) and Hg(II)1 Introduction2 Experimental2.1
Materials2.2 Microwave-assisted preparation of polyacrylonitrile
fiber modified by IDA2.3 Characterization of PANMW-IDA2.4
Adsorption experiments2.4.1 Effect of pH2.4.2 Adsorption
kinetics2.4.3 Adsorption isotherms
3 Results and discussion3.1 Preparation of PANMW-IDA fiber under
MW irradiation3.2 Characterization of PANMW-IDA3.3 Adsorption
performance of PANMW-IDA3.3.1 Effect of pH3.3.2 Effect of contact
time and adsorption kinetics3.3.3 Adsorption isotherms3.3.4
Adsorption thermodynamics parameters
3.4 Comparison between PANMW-IDA and other adsorbents
4 ConclusionsAcknowledgmentsReferences