Enhanced dechlorination of tetrachloroethylene by polyethylene glycol-coated zerovalent silicon in the presence of nickel ions

In this study, the combined effect of polyethylene glycol (PEG) and nickel ions on the dechlorination of tetrachloroethylene (PCE) by zerovalent silicon (Si(0)) under anoxic conditions was investigated. PEG was first coated onto the surface of Si(0) to form PEG-coated Si(0) (Si-pEG) and the concentration effect of Ni(II) ions at 0.001-2 mM on the dechlorination of PCE by Si-pEG was evaluated and optimized. Results of X-ray photoelectron spectroscopy and electron probe microanalysis showed that addition of PEG can not only inhibit the formation of SiO2 but also change the distribution pattern of SiO2 from homogeneous distribution to discrete and localized dispersion, resulting in the enhancement of dechlorination efficiency and rat of PCE by Si(0). The dechlorination of PCE by Si-pEG followed pseudo-first-order kinetics and the pseudo-first-order rate constant (k(obs)) for PCE dechlorination was 0.36 +/- 0.02 h(-1). Addition of Ni(II) exhibited the synergistic effect on the enhanced dechlorination of PCE by Si-pEG, and the maximum k(obs) for PCE dechlorination was 0.79 +/- 0.02 h(-1), which corresponded to 220-335 times higher than that by Si(0) alone. Hydrogenolysis and hydrodechlorination occurred simultaneously for PCE dechlorination by bimetallic Ni/Si-pEG system in the presence of Ni(II) ions, and the product distribution was highly dependent on the mass loading of Ni ions. The surface coverage of Ni onto SjpEG was used to well describe the synergistic effect of Ni(II) and Si-pEG on the enhanced dechlorination of PCE by Si(0) under anoxic conditions. (C) 2013 Elsevier B.V. All rights reserved.