Rapid dechlorination of chlorinated organic compounds by nickel/iron bimetallic system in water

Tong et al.1J Zhejiang Univ SCI 2005 64(7):627-631627Jourmal of Zhejiang University SCIENCEISSN 1009-3095htp://ww.zju.edu.cn/jzusJzuUSE-mail: jzus@zju.edu.cnRapid dechlorination of chlorinated organic compounds bynickel/iron bimetallic system in waterTONG Shao-ping (童少平)1.2, WEI Hong (魏红)，MA Chun-an (马淳安), LIU Wei-ping (刘维屏)(College of Chemical Engineering and Materials Science, State Key Laboraory Breeding Base of Green Chemistry-Synthesis Technology,Zhejiang University of Technology, Hangzhou 310032, China)(Institute of Environmental Science, Zhejiang University, Hangzhou 310029, China)*E-mail: sptong@zjut.edu.cnReceived Jan. 20, 2005; revision accepted Mar. 28, 2005Abstract: Detoxification of chlorinated organic compounds via reaction with nickel/iron powder was implemented in aqueoussolution. Compared to iron, nickel/iron bimaeallie powder had higher hydrodechlorination activities for both atrazine (ATR) andp-chlorophenol (pCP); nickeliron (2.96%, w/w) was shown to have the largest specific surface area and the optimum proportionfor the dechlorination of both ATR and pCP. Electrochemical measurements showed that the adsorbed hydrogen atom on thenickel must have been the dominant reductive agent for the dechlorination of both ATR and pCP in this system.Key words: p-Chlorophenol, Atrazine, Nicke/iron, Catalytic reduction dechlorinationdoi:10. 163 1/jzus 2005.A0627Document code: ACLC number: X703INTRODUCTIONhigh reactivity for treating low-molecule chlorinatedhydrocarbons and chlorinated phenols (Rosy et al,In the chemical process industry toxic and 1995; Wei JJ. et al., 2004), nicke/iron also provednon-biodegradable chlorinated organic compounds,effective for treatment of polychlorinated hydrocar-such as solvents, pesticides, medicine intermediates, bons (Quan et al, 1998). However, some worksetc., are produced in large quantities that present a showed that the catalytic reactivity of bimetallic sys-major environmental problem. Different methodstem always depends on the properties of chlorinatedhave been developed to treat water containing chlo- organic compounds (Quan et al, 1998; Kim andrinated organics. Reductive dechlorination technol- Carraway, 2000).ogy using zero-valent iron is considered to be aOur previous work addressed the effect of Ni/Fepromising remediation method (Schlimm and Heitz, molar ratio and different pH on the dechlorination1996; Balmer and Sulzberger, 1999; Claudia et al, efficiency of ATR, but we still have not studied the2000; Ghauch and Suptil, 2000).characteristics of Ni/Fe catalyst and the dechlorina-The reduction potential of Fe' (he standard tion mechanism of ATR (Wei H. et al, 200). For thecorrosion potential: -0.441 V) for the dechlorinationabove reasons and the cost of palladium, we studiedof some chlorinated organic compounds is too high tothe relationship between surface characteristics ofbe feasible (Graham and Jovanovic, 1999), so someNi/Fe catalyst and its catalytic activity on thebimetallic system based on zero-valent iron was in-dechlorination of both chlorinated heterocyclicvestigated recently. For example, palladium/iron hascompound- atrazine (ATR) and chlorinated aromaticcompound- -p-chlorophenol (pCP). The dechlorina-Project (No.30270767) spported by the National Naturl Science tion mechanisms中国煤化工invesFoundation of ChinaTYHCNM HG628Tong et al.1J Zhejiang Univ SCI 2005 64(7):627-631MATERIALS AND METHODSMatheson and Tratnyek (1994) reported that thereactive sites on the metal surface were involved inIron powder: (9%, 40~70 mesh), NiSO:6H2O dechlorination reactions, so metal surface area andwas of analytic purity; methanol was HPLC reagent;condition would strongly influence the reductive rateATR was purchased from Chemical Service (USA，of chlorinated organic contaminant. The surfacepurity>99%) and pCP from Shanghai Reagent Fac- morphological charateristics of iron and nickelirontory (China, purity>99%). Nickel/iron bimetallic(2.96%, w/w) powders are shown in Fig. 1 showingpowder was prepared according to Wei H. et that the surface of 2.96% nickeliron was sponge-likeal.(2004).with the nickel dispersed on iron surface, so the loadExcept otherwise specified, the concentrations of nickel could probably enlarge the specifc surfaceof ATR and pCP were 20 mg/L and 200 mg/L, re-area of the iron powder and present more reactivespectively. Stock solution (300 ml) was used in each sites.experiment with the added amount of nickel/ironcatalyst being 9.0 g/L. The pH of the solution wascontrolled by 809 Titrando (Metrohm) maintained at2.0 with 1.0 mol/L H2SO4. Corresponding sample(3.00 ml) was removed periodically and filteredthrough 0.45 um membrane for HPLC analysis. Allthe experiments were conducted at room temperature.Linear voltammetry measurements were per-formed in a three-electrode cell using a Model 273Apotentiostat. The reference electrode was saturateda)calomel electrode (SCE); the counter electrode andFig.1 SEM image of iron powder (a) and 2.96% Ni/Fe (b)working electrode were Pt flake and stainless steel (orporous nickel), respectively. The apparent area ofTo confirm the possibility of the above conjec-working electrode was always 1.0 cm2. The solutions ture, the specific surface areas of different nickel/ironwere deaerated with N2 for 30 min before every catalysts were measured by N2-BET. Fig.2 showselectrochemical measurement and protected by N2clearly that the specific surface areas of nickel/ironduring all the experiments.bimetallic powders varied with the increase ofATR's concentration was analyzed by HPLC nickel's loading and that the catalyst of 2.96%(Shimadzu LC-10Advp). The separation column wasnickel/iron had maximum specific area (11.671 m'/g).YwG C18 (10 pum), and the mobile phase was 65:35methano/water solution, flow rate was 0.80 ml/min;12.0 tpCP concentration was analyzed by HPLC (Wa-。10.5-ters1525- 2996). The separation column was Symme-” 9.0try C18(5 um), and the mobile phase was 50:50methanol/4% acetic acid solution (V/V), flow rate6.was 0.80 ml/min.The amount of nickel loading on iron was de-3.0-terminedby atom absorption spectrometry (AAS,Analytik Jena GmbH, Germany); the morphological-0.5 0.0 0.5 1.0 1.52.0 2.5 3.0 3.5structure of nickel/iron was viewed with a scanningelectron microscope (SEM, Model S-570, Hitachi);Ammount ofNi (%)and its surface area was measured by N-BET (Model Fig.2 Specifc surface areas of catalysts with dfferentnickel/iron proportionsST-03, Beijing).Effect of nickel/iron proportion on dechlorinationRESULTS AND DISCUSSIONefficiencies of both| 中国煤化工ienciesCharacterization results of nickel/iron powderThe ATR andMHCNMHGTong et al.1J Zhejiang Univ SCI 2005 64(7):627-631629achieved by different nicke/iron catalysts are shown that dechlorination of chlorinated aromatic compin Fig.3 and Fig.4, respectively. Fig.3 and Fig.4 in- is more difficult than that of chlorinated heterocyclicdicate that dechlorination efficiencies of both ATRcompound under the same conditions.and pCP maximized at 2.96% nicke/iron, whichaccorded with the results obtained with various ofCatalytic reduction mechanismspecific surface area of different nicke/iron catalysts.The above experimental results show that ATRThe above results also indicate that the dechlorination and pCP can be cataltically reduced effectively byefficiencies of both ATR and pCP on nickeliron nickel/iron system, and that the reducing agents in-bimetallic particles could increase when more catalyst cluding Fe' and adsorbed hydrogen atom on thewere added to the solution. For example, the dechlo- nickel might be responsible for their dechlorination.rination eficiencies of ATR by 2.96% nickel/iron To clarify the mechanism of their dechlorination ofcatalyst loaded with 3.0 g/L, 6.0 g/L and 9.0g/L in 20 nickeliron, the linear sweep voltammetrical curvemin were 30.2%, 63.5% and 95.5% under the samewas measured using model 273A potentiostat. Figs.5aconditions, respectively; the pCP dechlorination effi- and 5b show voltammetrical curves of ATR on theciencies obtained by different concentrations of electrodes of stainless steel and porous nickel elec-2.96% nickel/iron catalyst had similar results. After trodes. It can be seen that hydrogen gas was formedcomparison ofFig.3 and Fig.4, it can be concludedobviously on these two electrodes at- -0.6 V (vs SCE)100 F70原90F60|0-70F0F240300t昌200[-0.50.00.51.01.52.02.53.0 3.5-0.5 0.00.51.01.52.02.53.03.5Ammount ofNi (%)Fig.3 Effect of nickel/iron proportion on the dechlorina- Fig.4 Effect of nickel/iron proportion on the dechlorina-tion efficiency of ATRtion efficiency of pCPReaction time: 20 min; pH: 2.0; catalyst loaded: 9.0 g/LReaction time: 90 min; pH: 2.0; catalyst loaded: 9.0 g/L542F---- 50 mg/Lp0|官3---- 50 mg/L pCP8f62-自4o0-0.2 -0.3 -0.4 -0.5 -0.6 -0.7E (V)vs SCEE(V) vs SCE(a(bFig.5 Voltammetrical curves of pCP solution at different electrodes. Scan中国煤化工(a) Stainless steel; (b) Porous nickelTHCNM HG630Tong et al.1J Zhejiang Univ SCI 2005 64(7):627-631in the blank solution (pH=2.0 of H2SO4). However,Ni'/nFe'+H+ →,Fe* +Hm -Ni/(n-,)Feno reductive peak was also observed on both elec-trodes at the potential of higher than -0.6 V when(1)ATR was added to the solution. Voltammetry meas-urement for pCP showed similar results as shown inHmm - Ni°/(0-)Fe' +R-Cl→Figs.6a and 6b. The above results indicated that Fe'was not the cause of dechlorination of ATR and pCPlFe' +R-H+CIr (2)because of its high reduction potential, the adsorbedhydrogen atom on the nickel must be the main re-ductive agent for their dechlorination under theseHaom - Ni°Fe' +H*→experimental conditions. The above results were alsoreported by Kulikov et al.(1996) and Lin and Tseng-Fe+ + Ni%/(n - 1)Fe' +H2↑(Side reaction) (3)(1999).Ni%/nFe' +2H*→Fe+t +H2↑+ Ni'/(n- l)Fe' (Side reation) (4O2(g)+2H2O+4e→40H(53F --- 20 mg/L ATRAccording to this mechanism, dechlorination)Freactions of these two types of chlorinated organiccompounds have the same reductive agent (adsorbedhydrogen atom on the nickel). Except Eq.(1), it is alsopossible to generate adsorbed hydrogen atom when-0.2 -0.3 -0.4 -0.5 -0.6 -0.7hydrogen gas becomes dissociatively sorbed onto theE (V)vs SCEnicke/iron catalyst. The dependence of catalytic re-(a)activity of bimetallic system on the properties ofchlorinated organic compounds for their dechlorina-16tion should be attributable to mainly the stability of14|their C-Cl bond. Eq.(5) also indicates that the dis-22solved oxygen in water may compete for the electrons一Blank---- 20 mg/L ATRprovided by Fe' reaction with H" , which lowers the目8dechlorination efficiency, so deoxygenation in water自4can improve the dechlorination rate of chlorinated2organic compounds.oCONCLUSION(b)Nickel/iron had great catalytic efficiency for theFig.6 Voltammetrical curves of ATR solution at differentdechlorination of both ATR and pCP in water, and thedechlorination efficiency depended very much onScan rate: 220 mV/s; (a) Stainless steel; (b) Porous nickelboth nickel/iron proportion and the catalyst concen-tration. The experimental results revealed that 2.96%nicke/iron had largest specific surface area and wasWithout regard todehclorinated products ofthe optimum proportion for dechlorination of bothATR and pCP, the dechlorination mechanisms of the ATR and pCP. Electrochemical measurementsabove two chlorinated organic compounds can be showed that the adsorbed hydrogen atom on theexpressed by following chemical reactions:nickel must have b中国煤化工agentHCNM HGTong et al.1J Zhejiang Univ SCI 2005 64(7):627-631631ction dechlorination of chlororganic compounds on car-catalytic reactivity of bimetallic system on the prop-bon cloth and metal-modified carbon cloth cathodes.Electrochimica Acta, 41(4):527-531.erties of chlorinated organic compounds for dechlo-Lin, H.C, Tseng, S.K, 1999. Electrochemically reductiverination should be mainly attributable to the stabilitydechlorination of pentachlorophenol using a high over-of their containing C-CI bond.potential zinc electrode. Chemosphere, 39( 13):2375-2389.Matheson, LJ.. Tratnyek, R.G, 1994. Reductive dehalogena-Referencestion of chlorinated methanes by iron metal. Environ. Sci.Balmer, M.E, Sulzberger, B., 1999. 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Dechlorination oftreatment process: reductive dehalogenation of chlorin-ated hydrocarbons by metals. Environmental Progress,p-chlorophenol on a Pd/Fe catalyst in amagetically stabi-lized fluidized bed; Implications for sludge and liquidWei, H, Tong, S.P, Wang, HY,, Liu, W.P, 2004. Rapid:38-47remediation. Chemical Engineering Science, 54(15-16):3085-3093.treatment of atrazine- contaminated water by nickel/ironKim， Y，Carraway, E.R， 2000. Dechlorination of penta-bimetallic system. Journal of Environmental Sciences-China, 16(6):925-927.chlorophenol by zero valent iron and modified zero valentVei, JJ, Xu, X.H, Wang, D.H, 2004. Catalytic dechlorina-irons. Environ. Sci. Technol, 34(10):2014-2017.Kulikov, S.M., Plekhanov, V.P., Tsyganok, A.I, Tsyganok,tion of o-chlorophenol by nanoscale Pd/Fe. Journal ofEnvironmental Sciences-China, 16(4):621-623.A.I, Schlimm, C, Heitz, E, 1996. 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