Subscriber access provided by CORNELL UNIVERSITY LIBRARY Article Novel Magnetically Doped Epoxide Functional Cross-linked Hydrophobic Poly(lauryl methacrylate) Composite Polymer Particles for Removal of As(III) from Aqueous Solution Rukhsana Shabnam, Muhammad A. Rahman, Muhammad A. J. Miah, Mostafa K. Sharafat, Hasan M. T. Islam, Muhammad A. Gafur, and Hasan Ahmad Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01741 • Publication Date (Web): 14 Jun 2017 Downloaded from http://pubs.acs.org on June 15, 2017 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. 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" $& ' Rukhsana Shabnam†, Muhammad A. Rahman†, Muhammad A. J. Miah†, Mostafa K. Sharafat†, Hasan M. T. Islam‡, Muhammad A. Gafur§, Hasan Ahmad*† † Department of Chemistry, Rajshahi University, Rajshahi 6205, Bangladesh ‡ Department of Chemistry, Begum Rokeya University Rangpur, Rangpur 5400, Bangladesh § Pilot Plant and Process Development Centre, BCSIR, Dhaka 1205, Bangladesh *Phone +88507215711107; E5mail: samarhass@yahoo.com; hahmad@ru.ac.bd 1 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 $(')#$ )* Superparamagnetic iron oxide nanoparticles have been found suitable as adsorbent materials for the removal of As(III) from aqueous solution. In this investigation the usefulness of magnetically doped epoxide functional cross5linked poly(lauryl methacrylate) (PLMA) composite polymer particles as an adsorbent bed for the removal of As(III) ions has been evaluated. The epoxide functional composite polymer particles are prepared by seeded polymerization of glycidyl methacrylate (GMA) in presence of crosslinked poly(LMA5 divinylbenzene), P(LMA5DVB), seed particles. The surface of prepared composite polymer particles is finally doped with Fe3O4 nanoparticles. The epoxide functional magnetic composite polymer particles have been named as P(LMA5DVB)/PGMA/Fe3O4. A pH and contact time dependent adsorption behavior of As(III) is observed on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. The equilibrium (qe) reached after 180 min and a highest removal efficiency of 57.98% is attained at pH 5.0. The adsorption isotherm strictly followed Langmuir model with maximum theoretical adsorption capacity (qm) reached 66.23 mg/g of particles at 323K. Batch kinetic sorption experiments showed that a pseudo5second5order rate kinetic model is more applicable. The study of thermodynamic equilibrium parameters suggested that adsorption of As(III) is endothermic and spontaneous. The adsorbent could be regenerated partially by treatment with 0.01 M NaOH, retaining about 40% of the adsorption capacity after first time adsorption and then only slightly decreased. 2 ACS Paragon Plus Environment Page 2 of 39 Page 3 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research +, % )#- . )%The water that we use in many ways is highly contaminated by toxic metal ions which is a worldwide environmental problem including Bangladesh. Due to undegradable nature, toxic metal ions accumulate in humans and other living organisms which in turn enter the food chains.1 Among the different toxic metals existed in water effluents, arsenic (As) is the most hazardous element. It is a metalloid, possessing both metallic and non5metallic properties. Short and long term intake of As contaminated water can possess risks for human health related problems such as spontaneous pregnancy loss, respiratory complications, immunological system disorders, kidney cancer as well as changes in pigmentation, skin thickening (hyperkeratosis), neurological disorders, muscular weakness, loss of appetite, nausea and black foot disease.257 Acute As poisoning causes vomiting, oesophageal and abdominal pain, and bloody “rice water” diarrhea.8510 According to US Environmental Protection Agency, EPA, the maximum contaminant level is 50 µgL51 which has recently been refixed to 10 µgL51.11,12 As is mobilized in surface and ground water by a variety of ways such as natural weathering, chemical and biological reactions, volcanic eruptions and other anthropogenic activities.13 In addition mining activities, combustion of fossil fuels, uses of arsenic containing pesticides, herbicides, bactericides, wood preservatives, paints, drugs, dyes as well as arsenic additives to livestock feed add extra impact to the problem.14,15 The oxidation state of As plays an important role since it determines the toxicity, the sorption behavior and the mobility in the aquatic environment. As exists in four different oxidation states namely −3, 0, +3 and +5.16 Two inorganic forms of As are common in natural waters: arsenite (AsO33−) and arsenate (AsO43−), referred to as As(III) and As(V). Pentavalent (+5) or arsenate species are AsO43−, HAsO42−, H2AsO4−, while trivalent (+3) arsenites include 3 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 As(OH)3, As(OH)4−, AsO2OH2− and AsO33−. Pentavalent species predominates and are stable in oxygen rich aerobic environments while trivalent arsenites predominate in moderately reducing anaerobic environments such as surface and groundwater.17 As(V) is believed to be less toxic than As(III) and is the main species in natural waters.10 Numerous technologies such as oxidation,18 precipitation or coprecipitation,19,20 coagulation,21,22 sorption,23,24 ion5exchange,25,26 reverse osmosis,27 and electrokinetic methods28 have been studied for the removal of As from water. But the use of these methods is limited due to high operation and waste treatment costs, high consumption of reagents and large volume of sludge formation.29 But generation of high quality effluent adsorption technique is recognized as a most promising versatile approach for the treatment of As contaminated water because of simplicity, low cost, high concentration efficiency, flexibility in design, operation and environment friendliness. In addition, adsorption processes are mostly reversible in nature. The adsorbents can be regenerated by suitable desorption processes for multiple use.30 Desorption processes has low maintenance cost, high efficiency, and ease of operation.31 Fe(III)5bearing materials has attracted much interest in As adsorption because of their high selectivity and affinity compared to other conventional adsorbent materials like activated carbon, soil, resin and alumina.32535 In a research Yean et al. reported that magnetite iron oxide adsorbed As at pH below 9 but desorbed while the pH is adjusted to more than 10.36 Chowdhury et al. studied the adsorption of As and Cr by mixed magnetite and maghemite nanoparticles from aqueous solution and obtained maximum adsorption at pH 2.37 Morillo and his group studied the removal of As(III) and As(V) from acidic solutions with novel forager sponge5loaded superparamagnetic iron oxide nanoparticles.38 In acidic pH range, most of the As species in aqueous solution are negatively charged. Thus electrostatic attraction among magnetite5 4 ACS Paragon Plus Environment Page 4 of 39 Page 5 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research maghemite nanoparticles and metal species favored the removal of As compounds from water solution. However, the naked iron oxide magnetic nanoparticles are often insufficient for their poor colloidal stability, hydrophilicity, contamination and difficulty for further functionalization.39 Moreover, particles in the nano5range despite being having high surface activity are not suitable for designing chromatographic adsorption bed because of the drainage probability with the effluent and hence could produce iron oxide contaminated effluent. In this regard for efficient removal of As, the use of micrometer5sized composite materials with magnetite (Fe3O4) shell layer could limit the washing out effect of adsorbent with discharged effluent. In this investigation preparation and finally application of micron5sized epoxide functional magnetically doped hydrophobic poly(lauryl methacrylate5 divinylbenzene)/poly(glycidyl methacrylate)/Fe3O4 abbreviated as P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles will be discussed by measuring the adsorption behavior of As(III) from aqueous solution. LMA is a well5known hydrophobic long alkyl chain monomer and its polymer/copolymer offers extensive application potential as resins for chromatographic separation, water purification, oil absorbency agents, viscosity modifiers and oil5soluble drag reducers.40542 The modification of crosslinked hydrophobic P(LMA5DVB)/PGMA composite particles by Fe3O4 nanoparticles is expected to promote easy separation as well as recovery from the dispersion medium following applications. Moreover the presence of epoxide functionality on the surface would help to bind the iron oxide nanoparticles with magnetic composite polymer particles via complexation and therefore would prevent their leaching into the effluent during water treatment.43 One more advantage of this hydrophobic micron5sized epoxide functional P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is that they are useful for the removal 5 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 of hydrophobic contaminants like textile dyes, organic pollutants, pesticides etc. from wastewater.44 /, ' /,+, % , LMA from Fluka Chemika (Switzerland) was washed with 10% NaOH aqueous solution to remove any inhibitor and finally passed through activated basic alumina by column chromatography. Crosslinking agent DVB from Sigma5Aldrich, Chemie (USA) (80% grade) was purified with aqueous 10% NaOH solution and subsequently dehydrated by stirring with anhydrous CaCl2. Benzoyl peroxide (BPO) from BDH Chemicals Ltd. (UK) was recrystallized from methanol and preserved in the refrigerator before use. Cationic azo5initiator 2,2′5azobis(25amidinopropane)hydrochloride (V550) from LOBA Chem., India, was recrystallized from water before use. GMA Fluka Chemika (Switzerland) and PVA from Thomas Baker (Chemicals) Limited (India) of molecular weight 1.4 x 104 gmol51 were used without purification. As2O3 from May & Baker (UK), ferric chloride hexahydrate (FeCl3.6H2O), ferrous sulfate (FeSO4), NH4OH, oleic acid, KI, SnCl2, CHCl3, sodium diethyldithio5carbamate (NaS.CS.N(C2H5)2.3H2O), Zn5granules and other chemicals were of analytical grade. Deionized water was distilled using a glass (Pyrex) distillation apparatus. Scanning electron microscopy, SEM was performed to see the particle size distribution with a SU8000 microscope (Hitachi, Japan) operating at a voltage of 20 kV. Vibrating sample magnetometer, VSM (MicroSense, EV9, USA) was used for studying the magnetic property of composite polymer particles. FTIR (Perkin Elmer, FTIR5100, USA) was used to see the structural composition of the particles surface before and after As(III) adsorption. Adsorption 6 ACS Paragon Plus Environment Page 6 of 39 Page 7 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research study was performed by SP5300 (OPTIMA, Japan) single and UV51650 pc (Shimadzu, Japan) double beam UV5visible spectrophotometers. /,/, " 0 $ 1(!2 3 $2 4 -5 , P(LMA5DVB) polymer latex particles were prepared by suspension polymerization of LMA (3 g) and DVB (3 g) in presence of polymeric stabilizer PVA (1.2 g) in 200 mL distilled water using BPO (0.12 g) as oil soluble initiator. The polymerization was carried out in a three5 necked round bottomed flask, mechanically stirred at 100 rpm and maintained at 75°C for 24 h under a nitrogen atmosphere. The P(LMA5DVB) copolymer particles were washed repeatedly with double distilled water. P(LMA5DVB)/PGMA composite polymer particles were prepared by seeded polymerization of GMA (1.5 g) in presence of P(LMA5DVB) latex particles (3 g) as seed particles dispersed in 150 g of distilled water utilizing V550 (0.03 g) as initiator. The polymerization was continued for 12 h in a three5necked round bottomed flask at 70°C under a nitrogen atmosphere. P(LMA5DVB)/PGMA composite particles were washed by replacing the continuous phase with double distilled water following repeated centrifugation prior to the characterization. Magnetically doped P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles were prepared by co5precipitation of Fe2+ (0.556 g) and Fe3+ (0.6255 g) from their alkali aqueous solution (molar ratio 1: 2) containing 20 g of 25% NH4OH and 2.5 g of P(LMA5DVB)/PGMA composite polymer particles in 150 g of water. The magnetic composite polymer particles were washed repeatedly by magnetic separation and decantation. /,4, ) $ ' , The extent of As(III) adsorption was studied using a batch mode of experiment which was carried out by mixing 0.05 7 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 g of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles with 30 mL of 10 mg L−1 As(III) solution in a 100 mL stopper glass bottle. For pH dependent study the experiments were conducted at variable initial pH (3 to 6). The arsenic5composite mixture was magnetically stirred for 180 min at 303K. The composite polymer particles were finally separated by applying external magnetic field followed by centrifugation at 12,000 rpm. Centrifugation technique was employed to avoid the presence of any nonmagnetic dust particles and to improve the accuracy of the measurement. The supernatant was transferred to As generator and 5 mL conc. HCl, 2 mL KI solution and 0.5 mL SnCl2 were added in it. The content of the flask was swirled and then allowed to stand for about 15 min to ensure complete reduction of As to +3 state. The absorber tube was charged with 4 mL of the AgS.CS.N(C2H5)2. Granular Zn (5 g) was added to the solution in the flask and then the hydrogen sulfide scrubber was immediately inserted. The evolution of arsine (AsH3) was 99% completed within 40 min and the mixture was heated for another 5 min in water5bath at 75°C to complete the reaction. The absorber solution was transferred and its absorbance was measured at the wavelength of 535 nm by a UV5visible spectrophotometer. The amount of As adsorbed was calculated by subtracting the concentration in the medium from that of initial concentration. Calibration graph was used for this purpose. Likewise contact time5dependent adsorption measurements with variable contact time (55 300 min) were carried out at the pH value of maximum adsorption (optimized from the above experiment) using the same procedure. For comparison, reference P(LMA5DVB)/PGMA composite polymer particles were also used to check the adsorption of As(III) under identical conditions at pH 5.0, optimized from pH dependent adsorption measurement on magnetic composite polymer particles. 8 ACS Paragon Plus Environment Page 8 of 39 Page 9 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research /,5, $ % " $ %%%! , Adsorption isotherm experiments were performed at different ) temperatures (293, 303, 313 and 323K) with different concentrations (5 to 15 mg L−1). The adsorption experiment was carried out for 180 min at pH 5.0 (optimum as found from the previous experiment). For each measurement, a mixture of 30 mL of respective As(III) solution was mixed with 0.05g composite particles. The absorption behavior of As on the composite polymer particles was measured using UV5Vis spectrophotometer as discussed above. The Langmuir model was used to explain adsorption process of homogeneous monolayer surfaces with the basic assumption that adsorption occurred at specific homogeneous sites of the adsorbent. Another model frequently used was the Freundlich to describe heterogeneous systems. Temkin adsorption isotherm that explains the chemisorptions mechanism of adsorption phenomenon was also used. The variation of the equilibrium association constant (Ka = KL) with temperature was analyzed in terms of van’t Hoff plots ln =− ∆ . + ∆ (1) from which the thermodynamic parameters: free energy change ( G◦); enthalpy change (∆H◦), and entropy change (∆S◦) were extracted. From the slope of the plot lnKa vs. 1/T of equation (1), the value of enthalpy change was determined. From the relationships: ∆ =− ln (2) =∆ − ∆ (3) and ∆ the values of G◦ and S◦ were estimated. 9 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 /,6, 7 " $ %%%! $ Page 10 of 39 , The time dependent rate of As(III) adsorption was determined by batch experiments. For this experiment, 0.3 g of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles were thoroughly mixed with 180 g of 10 mg L−1 As(III) solution. The pH value of the mixture was adjusted to 5.0 and the mixture was magnetically stirred at 303K for a period of 5–300 min (varying). Aliquots of residual As were analyzed at the different time intervals by a UV5visible spectrophotometer as described above. The adsorption kinetic data were fitted with a pseudo5first (Eq. 4) and pseudo5second5order models (Eq. 5): − !" =! # = +$ − (4) (5) % % !# Where qe and qt are the amounts of adsorbed As (mg g−1) at equilibrium and at any time t (min), respectively. k1 (min−1) and k2 (g mg−1 min−1) are the equilibrium rate constants for pseudo5first and 5second5order adsorptions, respectively. /,8, " $ %%%!, In order to evaluate the reuse of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles adsorption5desorption cycles were carried out. At first, 30 mL of 10 mg L51 As(III) solution was mixed with 0.05 g of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. The pH value was adjusted to 5.0 and the mixture was allowed to stand under stirring at 303K for 180 min. The composite particles were magnetically separated. The amount of adsorption was measured. Then for desorption, As(III)5adsorbed P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles were dried at 40°C for 24 h and then weighed up. Subsequently, the adsorbed As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles was extracted by treating with 30 mL of 0.01~0.03 M NaOH as eluent for 24 h at room temperature. Then, the composite polymer particles were magnetically separated followed by centrifugation at 12000 rpm, and the concentration of desorbed As(III) in the supernatant was determined by UV5Vis 10 ACS Paragon Plus Environment Page 11 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research spectrophotometer as discussed above. The recovered composite polymer particles were reused as adsorbent for As(III) adsorption. , At time t, the amount of adsorption, qt (mg g51) was calculated /,9, $ using the following formula: = '( )'" * (6) + where Ct (mg L51) is the liquid phase concentrations of As(III) at any time, C0 (mg L5 1) is the initial concentration of the dye in solution. V is the volume of the solution (L) and W is the mass of dry adsorbent (g). The amount of equilibrium adsorption, qe (mg g51), was calculated using the formula = '( )'# * (7) + where C0 and Ce (mg L51) are the liquid5phase concentrations of As(III) present initially and at equilibrium. The As(III) removal percentage,η was calculated as follows: η= '( )'# '( × 100 (8) where C0 and Ce (mg L51) are the initial and equilibrium concentrations of the As(III) in solution. The difference between experimental and calculated values was measured by the root mean square (rms) parameter and used to determine how well models represent the experimental data. Chi5square statistic (χ2) was determined as follows: /0 = ∑ 2!#34 )!5(6 7 % (9) !5(6 where qmod is the modeled amount of As(III) adsorbed (mg g−1) and qexp is the experimental amount of As(III) adsorbed (mg g−1). If data from the model are similar to the experimental data, χ2 will be small. Therefore, using the non5linear Chi5square test, it is necessary to analyze the data set to confirm the best5fit isotherm.28 11 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4, # '.0)' $ Page 12 of 39 %' .''%- SEM image of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles shows in Figure 1 implies that particles are bit polydispersed. This is the common feature normally observed for polymer particles prepared by suspension polymerization.45,46 The heterogeneous protruding surface structure of composite polymer particles suggests the deposition of Fe3O4 nanoparticles. The heterogeneous non5smooth surface structure confirms the modification of particle surface by Fe3O4 nanoparticles. Some free Fe3O4 nanoparticles may also have by5produced during in situ precipitation of Fe2+ and Fe3+ from alkaline solution. The average size and coefficient of variation of composite polymer particles are around 11.3 µm and 46% respectively. The EDX spectrum of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles (not shown) indicates the presence of signal for Fe (2.54 atom%) and the amount of O (atom%) increases to 23.49% from 21.9% after magnetization of P(LMA5DVB)/PGMA composite particles. +. SEM image of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. 12 ACS Paragon Plus Environment Page 13 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research The magnetization curve of separated P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles was recorded using VSM at room temperature (Figure S1). The nearly zero coercivity and the reversible nature of the magnetization curve confirm the superparamagnetic character of composite particles at room temperature. The value of saturation magnetization is ~3.6 emu/g. This result suggests that the prepared P(LMA5DVB)/PGMA/Fe3O4 composite particles possess strong magnetic property. It was also possible to separate the magnetic composite polymer particles from the treatment solution using external magnetic field without employing time consuming separation process like centrifugation and sedimentation. 4,+, $ ( " $ %%%!, The application potential of the prepared P(LMA5 DVB)/PGMA/Fe3O4 composite polymer particles was evaluated by studying adsorption behavior of As(III) from aqueous solution. The parameters measured are detailed below. 3.1.1. Effect of pH. The adsorption of adsorbate is often controlled by the pH of the solution as it will change both the activity of active sites of adsorbent and the state of adsorbate. Therefore it is necessary to optimize the pH value of the solution for understanding the adsorption behavior of As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. Figure 2 shows that the adsorption of As(III) increases from 1.95 mg g51 at pH 3.0 to 3.48 mg g51 at pH 5.0 and then decreases with further increase in pH value. Consequently, the removal or uptake efficiency of As(III) by P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles also shows similar behavior and reaches maximum (57.98 %) at pH 5.0 (see inset Figure). In general variation of pH affects the surface chemistry of the iron oxides. It is noteworthy to mention that above the pH value of 3.0, the hydroxyl groups at the surface of the iron oxide are doubly 13 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 14 of 39 protonated (5FeOH2+) and the surface charge of iron oxide is thus positive.47 While at a certain pH, the hydroxyl group is protonated with single proton (5FeOH) having no (net) surface charge on the iron oxide. The value of this pH, called the point of zero charge, ranges between 5.5 and 9.0 for iron oxides.47 At pH value higher than point of zero charge the hydroxyl group is deprotonated (5FeO5), and thus the iron oxide surface bears a negative charge. In the present investigation the maximum adsorption of As(III) at pH 5.0 is therefore due to the electrostatic attraction between the positive charge of the iron oxide surface and the anionic form of arsenite (AsO335). The iron oxide is negatively charged at pH values above the point of zero charge which causes electrostatic repulsive forces with negatively charged arsenite and hence decreases the amount of As(III) adsorption. Comparatively the adsorption magnitude of As(III) at pH 5.0 on the reference P(LMA5DVB)/PGMA composite polymer particles was almost zero (data not shown). This result indicates that the adsorption of As(III) by P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is resulted from the interaction with iron oxide nanoparticles rather than with functional epoxide groups of the polymer matrix. Few literatures are also available which supports the interaction of As with iron oxide nanoparticles.37,38 14 ACS Paragon Plus Environment Page 15 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research /. Effect of pH on adsorption of As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles at ambient temperature. Inset Figure shows the removal percentage of As(III). Conditions: As(III), 10 mg/L; Polymer solid, 0.05 g; contact time, 180 min; total volume, 30 mL; temperature, 303K. 3.1.2. Effect of Contact Time. Contact time is crucial for the determination of rate of adsorption process. The effect of contact time on the adsorption amount (mg g51) of As(III) was measured up to 300 min at pH 5.0 where the initial arsenic concentration was 10 mg L51 for 0.05 g of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. Figure 3 shows that initially the adsorption of As(III) is slow and gradually increases until attaining a steady value after reaching the equilibrium at about 180 min. This contact time was selected as the equilibrium time for subsequent experiments. The initial fast adsorption rate is due to higher initial concentration of As and large number of available vacant active sites on the composite particle surface. The adsorption did not increase beyond the equilibrium time owing to the significant decrease in the number of active sites on the adsorbent. It is worthwhile to note that a higher amount of 15 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 16 of 39 composite polymer particles (~0.1 g) is necessary to effectively reduce the As(III) concentration from 10 mg L51 to below the US EPA recommended level of 10 Yg L51. 4, Effect of contact time on the adsorption of As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. Conditions: As(III), 10 mg/L; Polymer solid, 0.3 g; total volume, 180 mL; pH, 5.0; temperature, 303K. 3.1.3. Effect of Initial Concentration and Temperature. The effects of initial As concentrations (C0) in the range of 5 to 15 mg L51 on the equilibrium amount of adsorption (qe) (investigated under the optimized conditions; pH: 5.0 and contact time: 180 min) at different temperatures are shown in Figure 4. This measurement was carried out to see the effect of initial concentration and temperature on the amount of adsorption rather than to find the equilibrium initial concentration. In the experimental range the amount of adsorption at different temperatures increases with the increase of initial concentration. The increase of initial concentration enhances the driving force for transferring As(III) ions from the aqueous phase to the composite particle surface and hence increases the interaction between As(III) and magnetic 16 ACS Paragon Plus Environment Page 17 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research nanoparticles present at the particle surface. This effect is more pronounced at higher temperature. Therefore, a slightly higher temperature is found to be favorable for the adsorption of As(III) onto P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. 5, Initial As(III) concentration and temperature dependent adsorption behavior on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. Conditions: Polymer solid, 0.05 g; total volume, 30 mL; contact time, 180 min; pH, 5.0. 3.1.4. Equilibrium Study. The factors such as heterogeneity/homogeneity of adsorbents, the type of coverage and possibility of interaction between the adsorbate species determine the distribution of the adsorbate species among liquid and adsorbent which can be described by the mathematical models of adsorption isotherms like Langmuir, Freundlich and Temkin. These isotherms relate equilibrium amount adsorbed per unit mass of adsorbent, qe, to the equilibrium concentration of adsorbate in the bulk fluid phase Ce. 17 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 18 of 39 The main point of assumptions of the Langmuir model48,49 are as the maximum adsorption occurs when a saturated monolayer of solute molecules is present on the adsorbent surface, there is no migration of adsorbate molecules in the surface plane and the energy of adsorption is constant. The Langmuir isotherm is given by: = !5 89 '# (10) :89 '# By plotting (1/qe) versus (1/Ce), the constants in the Langmuir isotherm can be determined making use of above equation rewritten as: !# =! + 5 (11) !5 89 '# where the Langmuir constants, qm represents the maximum adsorption capacity for the solid phase loading and KL represents the energy constant related to the heat of adsorption. The plots of 1/qe against 1/Ce for the experimental data (Figure 5) exhibit high correlation coefficient (R2>0.99) of the linearized Langmuir equation (Table S1). Comparative results reveal that the adsorption data fits the Langmuir adsorption isotherm best at 323K as correlation coefficient is maximum at this temperature. Overall, Langmuir model can explain the adsorption of As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. The calculated values of qm and KL obtained from the intercept and slope of the respective straight line are presented in Table S1. The maximum adsorption capacity (qm) of P(LMA5DVB)/PGMA/Fe3O4 for As(III) is 21.51 mg g51 at 293K and increases with increasing temperature. Thus corresponding to maximum adsorption capacity it is favorable to carry out adsorption at higher temperature. It can be mentioned that the surface of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is homogeneous and the adsorption of As(III) formed a monolayer on its outer surface.50 18 ACS Paragon Plus Environment Page 19 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research 6, Langmuir isotherms of As(III) adsorption on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles at different temperatures. Conditions: Polymer solid, 0.05 g; total volume, 30 mL; pH 5.0; contact time, 180 min. The dimensionless constant called the separation factor (RL) is an essential feature of the Langmuir isotherm model. This shows the nature of the adsorption process as unfavorable (RL>1), favorable (0<RL<1), linear (RL=1) or irreversible (RL= 0). From the Table S1, it is observed that the RL values are in the range of 0. 64×1055 to 5.57×1055, which are less than unity, indicating that the adsorption of As(III) onto P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is a favorable process and thus it can act as an adsorbent for As(III). 19 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 20 of 39 The Freundlich adsorption model is applicable to multilayer adsorption on a heterogeneous surface of the adsorbent and active sites with different energy. Both nonlinear and linear forms of Freundlich model are given as: = ;< >= = ?@ ?@ (12) ; + = ?@< (13) where KF (mg g51) indicates the multilayer adsorption capacity and n (g L51) represents the effect of concentration on the adsorption capacity and represents adsorption intensity. Figure S2 represents the linear plots of logqe versus logCe at different temperatures. The values of KF and n determined from the intercept and the slope are presented in Table S1. The Freundlich constants KF and n are in the range 0.3150.56 and 0.596451.1100 respectively. In the present study a value of n of above unity observed at 293K is indicative of cooperative adsorption, whereas at higher temperature a value for n below unity implies that multilayer adsorption is unfavorable but a monolayer adsorption is favorable.51 Hence the Freundlich model can explain the adsorption process with the best fit at 293K, as also supported by correlation coefficient (R2) which is relatively close to unity. The Temkin model explains the adsorbate5adsorbent interaction isotherms. This model considers that the heat of adsorption of molecules on the adsorbent surface decreased linearly with saturation due to the adsorbate5adsorbent interaction. The Temkin isotherm52 has been used in the following form: = A B< (14) A linear form of the Temkin isotherm can be expressed as: = 0.C C A ?@B + 0.C C A ?@< (15) 20 ACS Paragon Plus Environment Page 21 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research = D + E ?@< where, D = 0.C C A (16) ?@B and E = 0.C C A , R is gas constant (8.314 Jmol01K01), T is temperature (K). The sorption data can be analyzed according to equation (8). Therefore, one can determine the constants a and b from the plot of qe versus logCe. The values of the Temkin constants a and b are listed in Table S1 and the plot of this isotherm is shown in Figure S3. Correlation coefficient (R2) lies in the range of 0.95750.979 indicates that adsorptions of As(III) on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles can be explained well with Temkin model. A relative study of the three isotherm models suggests that at 293K the Langmuir isotherm is the best fit model because it has the higher correlation coefficient (R2 = 0.9990) compared to those of the Freundlich (0.998) and Temkin (0.979) models. Hence at 293K the adsorption of As(III) predominantly followed monolayer physisorption. But the lowest χ2 (0.0022) value confirms the best fitness of the Freundlich adsorption isotherm rather than the Langmuir (χ2 = 0.0031) and Temkin (χ2 = 0.027) models indicating the multilayer physisorption. This is probably because of the surface homogeneity of bulk of the composite, monolayer and multilayer physisorption predominates over chemisorption. At 303K, both the highest value of correlation coefficient, R2 (0.9987) and the lowest χ2 (0.0137) value confirm the best fitness of adsorption data with Langmuir adsorption isotherm indicating the monolayer physical adsorption of As(III) onto polymer composite particles. Again, at 313K and 323K, the Langmuir isotherm seems to be the best model because it has the higher R2 (0.9991 and 0.9998) and the lower χ2 (0.0035 and 0.0006) values than those of R2 (0.995, 0.996, and 0.957, 0.957) and χ2 (0.0091, 0.0075, and 0.1246, 0.1486) of the Freundlich and Temkin models respectively. Hence of the 21 ACS Paragon Plus Environment Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Page 22 of 39 three isotherm models, the Langmuir isotherm seems to be the best model at any of the experimental temperatures indicating physical sorption of As(III) onto the surface of P(LMA5 DVB)/PGMA/Fe3O4 composite polymer particles. 3.1.5. Thermodynamic Parameters. The variation of thermodynamic equilibrium constant Ka with temperature can be used to deduce the thermodynamic parameters via van’t Hoff equation. The free energy changes ( G0) are tabulated in Table 1 and the feasibility and spontaneity of the adsorption of As(III) onto composite polymer particles is confirmed by the negative values of G0.53 The magnitude of G0 increases with increasing temperature which suggests that the degree of spontaneity increases at higher temperatures. The values of H0 and S0 are found to be 61.46 kJ mol−1 209.7 J mol−1 K−1 respectively. The positive value of H0 shows that the adsorption is endothermic and the positive value of S0 indicates that the randomness increases at the solid/solution interface during the adsorption of the As. The positive value of H0 again confirms that higher temperature facilitates the adsorption of As(III) onto P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. The enthalpy value for a sorption process can also be used to distinguish between chemical and physical adsorptions. For chemisorption, values of enthalpy change ranges from 83 to 830 kJ mol51 or greater.54 The enthalpy change (61.46 kJ K51 mol51) in the present investigation therefor confirms the cooperative adsorption process. 22 ACS Paragon Plus Environment Page 23 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research ) +. Equilibrium Constants and Thermodynamic Parameters for the Adsorption of As(III) on P(LMA5DVB)/PGMA/Fe3O4 Composite Polymer Particles. Temperature (K) Ka×1052 (L mg51) 293 303 313 323 1.197761 1.573998 5.964693 10.484403 H° 51 (kJ K mol51) 61.46492 S0 (J K51 mol51) G0 (kJ mol51) 209.7361 510.7734 510.4533 57.3331 56.0535 3.1.6. Kinetic Studies. The time5dependent adsorption study of As adsorption on P(LMA5DVB)/P(GMA)/Fe3O4 composite polymer particles was performed and analyzed using pseudo5first and pseudo5second5order kinetic equations to understand the kinetic mechanism. Lagergren’s first5order rate equation,55 one of the most widely used equations for the adsorption of adsorbate from a solution is: log log !# !# )!" − $ . = 0.CH (17) C =− $H 0.C C . + log (18) In a true first order process logqe should be equal to the intercept of a plot of log(qe–qt) against t. The pseudo5second5order equation, also based on the adsorption capacity of the solid phase, predicts the behavior over the whole range of data. Furthermore, it agrees with chemisorption being the rate controlling step. Ritchie proposed a method for the kinetic adsorption of gases on solids considering it to be a pseudo5second5order reaction.56 According to Ritchie pseudo5second5order equation (Eq. 5) a plot of t/qt against t should give 1/qe from the slope. Both pseudo5first5order and pseudo5second order kinetic plots are linearized as illustrated in Figures 657. However, the experimental adsorption capacities and the theoretical ACS Paragon Plus Environment 23 Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 values estimated from the pseudo5first and second5order equations presented in Table 2 give different results. The theoretical qe value (1.245 mg g51) estimated from the pseudo5first5order kinetic model (Figure 6) is significantly different from the experimental (3.48 mg g51) ones. Thus, the pseudo5first order kinetic model cannot describe the adsorption of As(III) by P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. On the contrary theoretical qe value (3.773 mg g51) estimated from the pseudo5second5order kinetic model (Figure 7) is comparatively close to the experimental values. Thus, the pseudo5second5order equation is better to describe the kinetic data than the pseudo5first5order equation. 8. Pseudo5first5order kinetic plot for the adsorption of As(III) on P(LMA5 DVB)/P(GMA)/Fe3O4 composite polymer particles. ACS Paragon Plus Environment 24 Page 24 of 39 Page 25 of 39 9, Pseudo5second5order kinetic plot for the adsorption of As(III) on P(LMA5 DVB)/PGMA/Fe3O4 composite polymer particles. /, The Pseudo5First5Order and Pseudo5Second5Order Kinetic Constants for Adsorption ) of As(III) on P(LMA5DVB)/PGMA/Fe3O4 Composite Polymer Particles. Experimental (K) Temperature 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research 303 qe (mg g51) 3.48 4,/, # First5order kinetic k1×1052 qe 51 Second5order kinetic k2×1052 qe (min51) (mg g ) (g mg51 min51) (mg g51) 0.58 1.245375 29.94 3.773 , The recovery of adsorbent is an important ' issue from the perspective of economic feasibility, industrial application and environment safety. In the present study recovery of adsorbent was attempted by treatment with 0.0151.0 M NaOH for 24 h at room temperature. Treatment with stronger (>0.01 M) NaOH did not produce good desorption as the colloidal stability was affected. Desorption upto 40% of the adsorbed As(III) was achieved. The repeated adsorption study showed that three times regeneration cycles maintaining ~37% of adsorption capacity (Figure 8) can be achieved. ACS Paragon Plus Environment 25 Page 26 of 39 Industrial & Engineering Chemistry Research Thus the prepared P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles showed fair recycling potential for being used as an effective adsorbent. ! 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 " :. Relationship between regeneration cycles and the percentage removal of As(III) ions by P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles. Conditions: at initial concentration 10 mg/L, temperature 303 K, polymer solid, 0.05; total volume, 30 mL; pH 5.0, contact time, 180 min. 4,4, " $ %%%! $ , The bare epoxide functional polymer matrix has almost no affinity for As(III) as the magnitude of adsorption was close to zero. The interaction of As(III) with P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is further evaluated by FTIR spectra analysis. Before As(III) adsorption, the spectrum of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles shown in Figure S4 exhibits the characteristic bands due to stretching vibrations of Fe5O bonds at 562 and 493 cm51. After As(III) adsorption the stretching vibrations of Fe5O bonds are shifted to 531 and 485 cm51 and the peak shape bit changed/broadened indicating the interaction of Fe3O4 nanoparticles with As(III). The characteristic sharp signal for ester carbonyl group appears at 1730 cm51 and those of epoxide group appear at 991 and 915 cm51 respectively remained identical following As(III) adsorption. While the signal attributes to the stretching vibration of surface water ACS Paragon Plus Environment 26 Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research molecules and hydrogen bonded surface –OH groups appears at 3487 cm51 is also changed following As(III) adsorption, which indicates the coordination of As(III) with protonated hydroxyl groups (5FeOH2+) as well. Therefore it can be said with confidence that at pH 5.0 the adsorption of negatively charged arsenite (AsO335) ions on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles is driven by electrostatic attraction with the doubly protonated hydroxyl groups of iron oxide (5FeOH2+) nanoparticles doped on composite particle surface. It is to be noted that doubly protonated hydroxyl groups (5FeOH2+) and the positive surface charge of the iron oxide exist at lower pH value (< point of zero charge). P(LMA5DVB)/PGMA/FeOH + H3O+ + AsO335 → P(LMA5DVB)/PGMA/Fe(OH)2+ 5 AsO335 + H2O A probable second sorption option is complexation through the formation of inner5 sphere complex via a ligand5exchange mechanism.6,57,58 In this reaction arsenite oxyanion competes with and exchanges with protonated surface hydroxyl (5FeOH2+) groups at pH 5.0 to form both bidentate binuclear5bridging complexes and monodentate mononuclear complexes. The probable structure of inner5sphere complexes of As(III) on iron oxide surface are illustrated in Figure 9. ;, Mechanism of complexation of arsenite with protonated surface hydroxyl groups on P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles at pH 5.0. ACS Paragon Plus Environment 27 Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 From the view point of above mentioned mechanism it can be said that P(LMA5 DVB)/PGMA/Fe3O4 composite polymer particles exhibited considerable adsorption capacity at acidic pH range of 3.055.0 and hence can be useful for commercial exploitation purpose. A comparative study of As(III) adsorption by different materials and composites found in literature is shown in Table S2. In literature a variety of composite materials have been studied for treatment of As contaminated water. It is known that the adsorption magnitude is largely dependent on size and size distribution of composite materials and such data is not available in most cases. Based on this knowledge, nanomaterials are expected to offer higher adsorption capacity due to comparatively larger specific surface area. However, Table 4 indicates that Fe3O4 nanoparticles possessed abnormally low adsorption capacity. This result can be explained by considering the aggregation and subsequent reduction in surface area that often occurred for bare magnetic Fe3O4 nanoparticles. The initial concentration (2 mg L51) was also reportedly low. In our experiment the fixation of Fe3O4 nanoparticles on the polymer matrix prevented their aggregation and thus might contribute to higher adsorption capacity. Table S2 also suggests that biodegradable composite particles based on chitosan and cellulose exhibit the highest adsorption capacity. But these types of adsorbent materials would find limited application potential considering the reusability, stability and even sometimes can pose serious problem while disposing off As loaded sludge. 5, - 0.'%- ' P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles were prepared by a three5step process. The morphology and magnetic properties were confirmed from SEM image and VSM analyses. The application potential of P(LMA5DVB)/PGMA/Fe3O4 composite polymer particles as adsorbent for As(III) adsorption from aqueous solution was evaluated. The maximum adsorption capacities of the P(LMA5DVB)/PGMA/Fe3O4 composite polymer ACS Paragon Plus Environment 28 Page 28 of 39 Page 29 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 Industrial & Engineering Chemistry Research particles (0.05 g) for 10 ppm As(III) solution was found at pH 5.0 achieving a removal efficiency of 57.98%. The magnitude of As(III) adsorption increased with contact time and the maximum adsorption was attained after about 180 min and remained constant after equilibrium is reached. The amount of adsorption was dependent on the initial concentration of As(III) and higher temperature (323K) favored the adsorption. The dimensionless constant separator factor (RL) was less than unity, indicated the adsorption of As(III) on P(LMA5 DVB)/PGMA/Fe3O4 composite polymer particles as a favorable process and hence it could be used as an effective adsorbent for As(III). The correlation coefficients and model parameters of the Langmuir, Freundlich and Temkin adsorption isotherms confirmed that the Langmuir isotherm is the best model at any of the experimental temperatures to describe adsorption process. The lower value of ∆H0 clearly demonstrated that the interaction between As(III) and composite polymer particles was weak. The time5dependent adsorption study was performed and analyzed using pseudo5first and pseudo5second5order kinetic equations. A comparison between the experimental adsorption capacities and the estimated theoretical values confirmed that the pseudo5second5order equation can better describe the kinetic data than the pseudo5first5order equation. $''- %$) ' - ) ) " Figures listed S1, S2, S3, S4 and Tables listed S1, S2 as mentioned in the text. $ < The authors acknowledge the support from Central Science Laboratory, Rajshahi University, for necessary instrumental support. ACS Paragon Plus Environment 29 Industrial & Engineering Chemistry Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 # # ' (1) Wang, J.; Cheng, C.; Yang, X.; Chen, C.; Li, A. A New Porous Chelating Fiber: Preparation, Characterization, and Adsorption Behavior of Pb(II). Ind. Eng. Chem. Res. /=+4, 52 (11), 407254082. (2) Wai, C. M.; Wang, J. S.; Yang, M. H. 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