Conductive-polymer-supported palladium-iron bimetallic nanocatalyst for simultaneous 4-chlorophenol and Cr(VI) removal: Enhanced interfacial electron transfer and mechanism.

Nanoscale zerovalent iron (nZVI) reduction offers a wide range of applications in source-zone remediation, but the reactivity of nZVI is largely hampered due to its low electron-transfer ability and tendency to aggregate. Based on the dual function of conductive polymers (CPs) as support and electron transfer carrier, we combined CPs with nZVI and prepared a series of Pd/Fe bimetallic materials that successfully address the challenges of nZVI reduction. These Pd/Fe@CPs particles showed strong catalytic ability for the simultaneous removal of 4-chlorophenol (4-CP) and Cr(VI). The removal rate of 4-CP was significantly enhanced by 1.5-6.2 times after supporting Pd/Fe nanoparticles (NPs) with CPs. The enhanced reactivity of supported Pd/Fe NPs was attributed to their highly stabilized and dispersed state and the promoted electron transfer due to the synergistic effect between CPs and nZVI bimetallic particles. The various catalytic activity over Pd/Fe@CPs was attributed to the distinctive properties of CPs and their different interfacial electron transfer ability. Importantly, this study provides insights into distinguishing both mechanisms of direct electron transfer and atomic-hydrogen-mediated indirect electron transfer, and their quantitative relationship to the dehalogenation performance over Pd/Fe@CPs materials. This work provides better understanding of the remediation process and mechanisms of nZVI reduction.