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: pwang73@vip.sina.com (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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S. Deng et al. / Chemical Engineering Journal 276 (2015) 349357 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