Influence of nickel loading on reactivity of Ni/Fe bimetallic nanoparticles toward trichloroethene and carbon tetrachloride

Bimetallic Ni/Fe-nanoparticles has been developed to enhance the dechlorination reactivity of nano-sized zero-valent iron. The physical structures of Ni/Fe-NPs with Ni loading ranged from 0.5wt% to 20wt% and the structure dependent reactivity variation towards to trichloroethene (TCE) and carbon tetrachloride (CT) have been fully investigated. A Ni-accumulated surface can be observed for the Ni/Fe-NPs with high Ni loading (20 wt.%), and the structure of other Ni/Fe NPs were identified as a Ni/Fe alloy-like structure with 5wt% Ni/Fe NPs owning the highest surface area and Fe0 content. While the best CT dechlorination rate was 2.5-fold of B-nZVI at 5wt% Ni loading, the best TCE reduction was 12-fold of B-nZVI at medium Ni loading (3wt%-5wt%). Since the primary TCE degradation mechanism is via atomic hydrogen (H*) whereas degradation of CT proceeds via direct electron transfer, the more efficient reduction mechanism for the Ni/Fe NP system was preferably H* reduction. The reduction-rate and the by-products yield variation between medium loading((3wt%-5wt%) and low/high (0.5wt%,20wt%) loading was more significant for TCE than CT. It has been found that Medium Ni loading (3wt%- 5wt%) obviously boosted the β-elimination of TCE to VC due to good storage of H* in Ni catalyst. The production of H* and enhanced electron migration rate were well demonstrated by CV curve and Tafel curve, respectively. The occurrence location of direct electron transfer and H* catalyst in bimetallic Ni/Fe system was further discussed.