Concentration effect of copper loading on the reductive dechlorination of tetrachloroethylene by zerovalent silicon

摘要

The dechlorination of tetrachloroethylene (PCE) by zerovalent silicon (Si(0)) in the presence of lownconcentration of Cu(II) ion was investigated under anaerobic conditions. The mass loadings ofnCu(II) in the Si(0)-H2O system were in the range 0.06–3 wt% (0.02–1 mM). In addition, the X-raynphotoelectron spectroscopy (XPS) and electron probe microanalysis (EPMA) were used toncharacterize the change in chemical species and distribution patterns of metals, respectively.nResults showed that the pre-incubation time of 3 d was needed to activate the reactive sites ofnSi(0) before the dechlorination of PCE. Addition of low concentration of Cu(II) at 0.06wt%nsignificantly enhanced the dechlorination of PCE, while high concentration of Cu(II) would occupynthe reactive sites of Si(0), and subsequently decreased the dechlorination efficiency and rate ofnPCE. The pseudo first-order rate constant (kobs) for PCE dechlorination by 0.06wt% Cu/Si wasn0.028 h21, which was 2.8 times higher than that by Si(0) alone. However, the kobs for PCEndechlorination decreased to 0.0016 h21 when the loading of Cu(II) increased to 3 wt%. The EPMAnresults showed that the distribution of 0.06wt% Cu on the Si(0) surface was homogeneousnwithout any aggregation, which means that the maximum rate constant was observed before thentotal coverage of the active sites on the reductive metal by the catalytic metal layer. The surfacencoverage of Cu to Si(0) can theoretically calculate by estimation of the lowest energy fcc(111)ncrystallographic orientation. The calculated surface coverage of 0.06wt% Cu onto Si(0) wasnapproximately 43%, which is consistent with the experimental results obtained in this study.