Enhanced photocatalytic reduction of Cr(VI) on silver nanoparticles modified mesoporous silicon under visible light

Abstract

AbstractThe development of visible‐light photocatalysts with desirable material characteristics and efficient performance is an existing challenge for photocatalysis community. Herein, we report on the synthesis of silver nanoparticles (AgNPs) modified porous silicon (PSi) nanopowder and its effective use in the photo‐reduction of hexavalent chromium Cr(VI) to trivalent Cr(III) under direct visible light irradiation in the presence of citric acid. The PSi was prepared via simple stain etching of Si microparticles in HF/HNO3 aqueous solution, followed by the deposition of AgNPs onto PSi by the immersion plating technique. The developed photocatalyst composed of PSi with <20 nm mesoporous structure, decorated with crystalline 15‐50 nm AgNPs. Photocatalytic experiments using unmodified Si microparticles, either PSi or sonicated one, indicated inactive catalytic behavior toward the photo‐reduction of Cr(VI). Remarkable photo‐reduction efficiency (97.4%) was achieved after 180 minutes irradiation using the AgNPs/PSi sample. The efficient photo‐reduction capability of AgNPs/PSi photocatalyst is attributed to the enhanced separation between photo‐generated electrons and holes (e−‐h+) enabling better utilization of light, as revealed from the photoluminescence measurement. Additionally, the presence of citric acid in solution promoted greatly the photo‐reduction reaction as it acted as a hole scavenger, suppressing further the rate of e−‐h+ recombination through rapid consumption of photo‐generated holes. Excellent reusability of the current photocatalyst was evidenced by performing cyclic five runs with minimal reactivity loss. Results of synthesis, characterization, photocatalytic activity and reaction mechanism are thoroughly addressed and discussed.