Dechlorination of chlorinated hydrocarbons by bimetallic Ni/Fe immobilized on polyethylene glycol-grafted microfiltration membranes under anoxic conditions Ganesh K. Parshetti, Ruey-an Doong ⇑ Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, 101, Sec. 2, Kuang Fu Road, Hsinchu 30013, Taiwan article info Article history: Received 6 April 2011 Received in revised form 18 October 2011 Accepted 19 October 2011 Available online 23 November 2011 Keywords: Bimetallic Ni/Fe nanoparticles Immobilization Nylon-66 membrane Chlorinated hydrocarbons abstract In this study, the dechlorination of chlorinated hydrocarbons including trichloroethylene (TCE), tetra- chloroethylene (PCE) and carbon tetrachloride (CT) by bimetallic Ni/Fe nanoparticles immobilized on four different membranes was investigated under anoxic conditions. Effects of several parameters including the nature of membrane, initial concentration, pH value, and reaction temperature on the dechlorination efficiency were examined. The scanning electron microscopic images showed that the Ni/Fe nanoparticles were successfully immobilized inside the four membranes using polyethylene glycol as the cross-linker. The agglomeration of Ni/Fe were observed in poly(vinylidene fluoride), Millex GS and mixed cellulose ester membranes, while a relatively uniform distribution of Ni/Fe was found in nylon-66 membrane because of its hydrophilic nature. The immobilized Ni/Fe nanoparticles exhibited good reactivity towards the dechlorination of chlorinated hydrocarbons, and the pseudo-first-order rate constant for TCE dechlo- rination by Ni/Fe in nylon-66 were 3.7–11.7 times higher than those in other membranes. In addition, the dechlorination efficiency of chlorinated hydrocarbons followed the order TCE > PCE > CT. Ethane was the only end product for TCE and PCE dechlorination, while dichloromethane and methane were found to be the major products for CT dechlorination, clearly indicating the involvement of reactive hydrogen species in dechlorination. In addition, the initial rate constant for TCE dechlorination increased upon increasing initial TCE concentrations and the activation energy for TCE dechlorination by immobilized Ni/Fe was 34.9 kJ mol À1 , showing that the dechlorination of TCE by membrane-supported Ni/Fe nanoparticles is a surface-mediated reaction. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Chlorinated hydrocarbons such as trichloroethylene (TCE) and tetrachloroethylene (PCE) are one of the most commonly found hazardous organic contaminants in subsurface environments (USEPA, 1997). These solvents are often used as degreasing agents in the automotive, metal, and electronic industries, and released into the environment via improper disposal. It has been demon- strated that both biotic and abiotic reactions contribute to the reductive transformation of contaminants under anoxic conditions (Lee et al., 2004; Doong and Chiang, 2005; Chu et al., 2006; Dar- lington et al., 2008; Elsner et al., 2008; Maithreepala and Doong, 2009; Lee and Doong, 2011). Over the past decades, zerovalent metals and bimetallic systems such as Pd/Fe, Ni/Fe, Ni/Si and Cu/Fe have been demonstrated to be an effective approach to treat the contaminated water containing chlorinated hydrocarbons by enhancing the dechlorination rate as well as by altering the dechlo- rination pathways (Li and Farrell, 2001; Zhang, 2003; Choi et al., 2008; Lee and Doong, 2008; Tee et al., 2009). However, the agglomeration and decrease in reactivity of nanoparticles resulting from the formation of metal oxide films have also been reported. The attachment of metallic particles onto polymer membranes and supports can reduce the particle loss and particle agglomera- tion (Xu and Bhattacharya, 2008; Parshetti and Doong, 2009). Sev- eral stabilizers including starch (He et al., 2007), hydrophilic carbon, poly (acrylic acid) (PAA) (Schrick et al., 2004), and carboxy- methyl cellulose (Wang et al., 2010) have been used to prevent the aggregation of nanoparticles in aqueous solutions. The use of por- ous microfiltration membranes as the support is of great interest because of their open structures and large pore sizes (Xu and Bhattacharya, 2008). PAA is one of the often used cross-linkers to immobilize bimetallic nanoparticles onto various membranes, such as poly(vinylidene fluoride) (PVDF) and cellulose acetate, for dechlorination of TCE (Xu and Bhattacharya, 2005, 2008; Wang et al., 2008). Xu et al. (2005) synthesized the bimetallic Ni/Fe and Pd/Fe nanoparticles in the PAA/PVDF composite membrane for the reductive dechlorination of TCE. In addition, the nanoscale zerovalent iron (NZVI) has been immobilized onto poly(vinyl alcohol) (Shimotori et al., 2004) and high-density polyethylene 0045-6535/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2011.10.028 ⇑ Corresponding author. Tel.: +886 3 5726785; fax: +886 3 5718649. E-mail address: radoong@mx.nthu.edu.tw (R.-a. Doong). Chemosphere 86 (2012) 392–399 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere