Siloxene: An advanced metal-free catalyst for efficient photocatalytic reduction of aqueous Cr(VI) under visible light

In this work, we reported the synthesis of siloxene catalysts from calcium silicide at various topotactic reaction conditions and demonstrated their photocatalytic activity for Cr(VI) reduction under visible light irradiations. The topotactic reaction time influenced the surface area, structure, and optical characteristics of the siloxene, which altered the Cr(VI) photocatalytic elimination efficiency. A large specific surface area (47.04 m(2) g(-1)) and a narrow bandgap (2.45 eV) with hydroxyl-terminated layered silicon of the S-12 h catalyst could enable more active sites for photocatalytic reaction, which results in the improved catalytic performance for Cr(VI) removal. The Density Functional Theory calculations proved the siloxene's direct bandgap feature and narrow bandgap. The initial Cr(VI) concentration, solution pH, temperature, inert gas, and different scavenger's effects on the photocatalytic performance of the S-12 h catalyst were also investigated. The S-12 h photocatalyst exhibited the Cr(VI) reduction efficiency of 98.6% for the electroplating wastewater that demonstrates the potential application in industrial for treatment of heavy metal ions removal.