Visible-light-enhanced Cr(VI) reduction at Pd-decorated silicon nanowire photocathode in photoelectrocatalytic microbial fuel cell.

Hexavalent chromium (Cr(VI)) is a prominent toxicmetal with significant adverse human health effects. Photocatalytic reduction of Cr(VI) to less-toxic trivalent chromium(Cr(III)) is a promising method for removing Cr(VI) fromaquatic environments. However, this technique often suffers fromelectron-hole recombination of semiconductors and poor reduction efficiency. The photoelectrocatalytic microbial fuel cell (Photo-MFC), which can use wastewater and light to recover electricity, has recently been proven to improve the separation of photocarriers of semiconductors and enhance cathodic reduction of pollutants. Here, the reduction of Cr(VI) was investigated in a Photo-MFC with a Pd-decorated p-type silicon nanowire (Pd/SiNW) photocathode and a bioanode under visible light. The Cr(VI) reduction efficiency reached 98.7% in 8 h under visible light, which was much higher than that under dark condition (56.2%) and open-circuit condition (19.4%). The enhanced Cr(VI) removal was mainly attributed to the synergistic effect of Pd/SiNWphotocathode and bioanode. Cr(VI) reduction in the Photo-MFC fitted wellwith pseudo-first-order kinetics. The kinetics constants and reduction efficiencies of Cr(VI) decreased with the increase of pH, initial Cr(VI) concentration and external resistance. This work provides a promising alternative to mitigate Cr(VI) pollution in aquatic environments. (C) 2018 Elsevier B.V. All rights reserved.