REMOVAL OF MERCURY FROM WATER USING POLYPYRROLE AND ITS COMPOSITES

Chinese Jourmal of Polymer Science Vol. 25, No. 4, (2007) 393-397Chinese Journal ofPolymer Science02007 World ScicnifcREMOVAL OF MERCURY FROM WATER USING POLYPYRROLEAND ITS COMPOSITESHossein Eisazadeh'Faculty of Chemical Engineering, University of Mazandaran, P.O. Box 484, Babol, lranAbstract One of the suitable methods for removing heavy metals from water is by using surface adsorption process. In thispaper, the preparation of polypyrrole and its composites as adsorbents are discussed and the capability of scpanating mercuryfrom water is investigated. The results indicated that the polypyrole and its cormposites are able to remove mercury fromaqueous media. Furthemore the adsorption percentage is related to the surface morphology, type of additives and itsconcentration.Keywords: Polyrrole and its composites; Mercury removal; Additives; Surface morphology.INTRODUCTIONThere are many studies on the importance of water quality and also on protection of different organic resourcesfrom wastewater entrance". Heavy metals such as mercury, lead, cadmium, copper, chromium and nickel aretoxic even in extremely minute quantities. Concentrations of such pollutants in environment have direct relationwith cities expansion and industries improvement and their disadvantages on environment and human health havebecome more obvious day by day2.Among these so-called pollutants, mercury (Hg) is the most toxic. Due to its low boiling point, Hg isvaporized during the high temperature incineration process. Therefore it enters the atmosphere easily and is lessinfluenced by operating parameters'3lIn recent years, considerable attention has been devoted to find new adsorbents. Fly ash from a thermalpower plant!4, waste slury from a fertilizer plant5, blast furnace industries!6] and photo film waste sludge'nhave been examined for removal of hexavalent chromium.Activated carbon is commonly used for removal of non-polar organic material in water and wastewaterS.Bentonite is used widely for adsorption of particles due to its high activated surface and their tendency to adsorbwater in the inter-layer sites!9!.The electophoresis data for polyaniline silia (PAn-SiO2), polyrole-silica (PPy-SiO2) and PPy-SnO2 :nanocomposites indicate that the surface of these particles are rich in inorganic oxide component and it is clearthat this will affect the surface charge of composite particlesto. The electr-active PAn-SiO2 and PPy-SiO2nanocomposites represent a potentially useful material for recovery of precious metals"I. A comparison of thereduction of gold from chloroauric acid solution by Py flms and powders clearly demonstrated the effect ofsurface is limited in this processl21. It was recently shown that neutral polypyrrole (PPy0) reversibly reacts withCr(VI) in aquecous sulfuric acid solutions to give Cr(I) and oxidized conducting polyrole (PPy+)"3! Theseparation of cation may depend on reduction/oxidation of PPy or metal ligand interaction|l4.Conductive electro-active polymers such as PPy possess some unique chemical and electrochemicalproperties. PPy is atractive as an electrically conducting polymer because of its relative ease of synthesis. Bulk*Corresponding author: Hossein Eisazadeh, E mail: cisazadeh@hotmai中国煤化工Received August 8, 2006; Revised September 21, 2006; Accepted SepteYHCNMHG394H. Eisazadehquantities of PPy can be obtained as fine powders using the oxidative polymerization of the monomer by selectedtransition metal ions in water or various other solutionshs”. The reaction of pyrrole with aqueous ferric chlorideis very rapid and the product is a black powder, which is insoluble in all common solvents(18]. The addition of asmall amount of appropriate polymeric additive such as poly(vinyl alcohol) to conductive polymers can changethe structure and the permeability of the film[!9.The main discussion of this paper is the removal of mercury by using surface adsorption and determining theability of polypyrole and its composites to renove merury from water.EXPERIMENTALInstrumentationA magnetic mixer model MK20, digital scale model FR 200, inductively coupled plasma (ICP) model vista-proand scanning electron microscope (SEM) Joel model LSM50A were employed.Reagents and Standard SolutionsAll reagents were used as received without further purification, unless stated otherwise. Distilled-deionizedwater was used throughout this work. Monomer of pyrrole was purified by simple disillation. Anhydrous ferricchloride was purified using simple filration. Materials used in this work were bentonite, activated carbonpowder, pyrrole (Aldrich), poly(vinyl alcohol) (PVA, weight-average molecular weight (Mw) = 15000, 10000)and poly(ethylene glycol) (PEG, Mw = 4000, 35000) obtained from Merck,Composite PreparationFeClz was used as the oxidant, with PVA, PEG, bentonite and activated carbon as additives. The reaction wascarried out in an aqueous media at room temperature for 5 h. The optimal conditions for composite formation aresummarized in Table 1.Table 1. Preparation of polypyrole compositesConcentration ofType of compositeType of adiveadditive (gL)Composite of polypyrrole with poly(vinyl alcohol) (Mw = 10000) poly(vinyl alcohol)1.5Composite of polypyrrole with poly(vinyl alcohol) (Mw = 15000) poly(vinyI alcohol).5poly(ethyleneComposite of polyprrole with polylethylene glyco)(M. =4000)glycolComposite of polyrole with poly(ethylene glycol) (Mw = 4000)3Composite of polypyrrole with poly(ethylene glycol) (Mw = 35000)5glycol)Composite of polyryrole with poly(cthylene glycol) (Mw = 35000)glyco)Composite of polypyrrole with activated carbonactivated carbonComposite of polypyrole with bentonitebentoniteReaction conditions: FeCl 53 g/L; Pyrrole 14.9 x 102 molL; Volume of solution 100 mL; Reaction time 5 h at roomtemperatureIn a typical experiment, 1 mL of pyrrole was added to a strred aqucous solution (100 mL) containing 5.3 gof ferric chloride and 1.5-3 g of one of the aditives. After 5 h polymer was filtered and to separate theoligomers and impurities, product was washed several times with deionized water and dried in room temperature.It should be mentioned that in the preparation of PPy composites when the amount of surface active agentssuch as PVA and PEG are low, the stabilization is inefficient and so the macroscopic precipitation of polymeroccurs.For determining the amount of mercury removal by PPy and its composites, 50 mL of differentconcentrations of mercury were mixed with 0.25 g powder of PPv and its comnnsites and then stired using中国煤化工TYHCNMHGRemoval of Mercury from Water Using Pobpyrrole and Is Compositesmagnetic mixer for 30 min and then was filtered respectively. The concentration of mercury from the resultantsolution was determined using ICP tes.RESULTS AND DISCUSSIONAdsorption is atibuted to the afnity interaction between the adsorbent's activated sites and the adsorbate. Theadsorption capacity is affected by the adsorbent's properties such as its structure, size and chemistry of thesurface. Activated carbon with low polar properties is a typical adsorbent20.Adsorption of the stabilizer on the PPy particles is primarily due to the hydrophobic component in thestabilizers, probably via a hydrogen bonding mechanism with the pyrrole N- -H groupl'".The chemical method can be a general and useful procedure to prepare conductive polymer and itscomposites. PPy and its composites were prepared by chemical method using different additives such aspoly(ethylene glycol), poly(vinyl alcohol), bentonite and activated carbon powder in an aqucous media.The conditions for preparation of PPy and its composites are sbown in Table 1. Different concentrations ofHg*(1.8x 10-,3x 10-, 6x 10- g/L) were prepared by solving Hg(NO)h in water and were used as inletsolutions. The average pH value of solutions used in these experiments was approximately 4. For determining theamount of mercury removal from different samples, 50 mL of preparedt mercury was mixed with 0.25 g ofvarious adsorbents such as polyrrole and its composites, bentonite and activated catbon powder for 30 minrespectively.After filtration the concentrations of solutions were analyzed by ICP and the resuts are shown in Table 2. Itshould be mentioned that the ICP is a very aggressive ion source. Because the source operates at a temperature of7000 K, virtually all molecules in a sample are broken up into their component atoms.As seen in Table 2, PPy has the desired procedure in mercury removal with 93% and can be improved to98.9% by using PPy composite with activated carbon powder. Also by using the composite of PPy with PEG andPVA, the amount of mercury removal from the solution reaches 97.9% and 96% respectively. So the separationof mercury from the solution by PPy and its composites is dependent on the ability of surface absorption.PEG and PVA are stbilizing agents and could afet the sie, morphology and the homogceneity ofparticles'2. 23), because the additives are adsorbed physically or chemically by the growing polymer, The role ofPVA and PEG on the surface of the PPy particles has to be studied so as to clanify is infuence on the structuralarrangement of the particles in the matrixl4.In Figs. 1 and 2, SEM micrographs of the PPy and its composites are shown. As it can be seen PPy particlessynthesized by suspension polymerization (without stabilizer) are larger than the PPy particles using surfaceactive agents. The tendency to form agglomerates is lower which leads to more homogenous distribution in thematrix._5 μm_Fig.1 Scanning electron micrograph of PPy in anFig. 2 Scanning electron micrograph of PPy compositeaqueous media without additivein an aqueous media using PEG (Mw = 35000, 3 g/L)Reaction conditions: FeC]z 53 g/L: Pyrole 14.9 x 10~2Reaction conditions: FeCl; 53 g/; Prrole 14.9x 102mol/L; Volume of solution 100 mL; Reaction time 5 hmol/L; Volume of solution 100 mL; Reaction time5 hat room temperature中国煤化工TYHCNMHG396H. EisazadehTable 2. The results of ICP test for mercury removalMercuryAverageRemovalmercuryconcentration concentrationremovalNo.Sarnpleconcentrationpercentageconcentration after removal after removal(mg/L)(wt%)(mg/L )Polypyrole1.2.40.060.1996.6793Polytrole30.3289.332 Composite of polypyrrolewith poly(vinyl alcohol)1.80.12595.2(Mw = 15000)Composite of polypyrrole93.673Composite of polypyrrolewith poly(vinyI alcohol)4.50.120.18)696(Mw = 10000)Composite of polypyrole60.24(Mw = 00000)4Cormposite of polypyrrolewith poly(ethylene glycol)4.0.11(Mw = 4000, 1.5 g/L)0.1098.33(Mw= 4000, 1.5 g/L)Composite of polypytrole0.090.149796.9(Mw = 4000, 3 g/L)96.83Mw = 4000, 3 gL)6 Composite of polypyrrolewith poly(ethyiene glycol)0.959897.9(Mw = 35000,3 g/L)0.1397.83(Mw= 35000, 3 g/L)7 Composite of polypyrole3.60.020.0498.89with activated carbon98.6798.9Cormnposite of polypyrole)90.0398.7with bentonitewith benloniteActivated carbon0.06598.40.0798.83Bentonite0.0359999.299.33 _中国煤化工MYHCNMHGRemoval of Mercury from Water Using Pobyprrole and lts Composites397CONCLUSIONSThe effect of PPy and its compositcs on the removal of mercury was investigated and the results indicatedthat all composites show good adsorption and remove high percentage of mercury. 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