Photoreduction of Cr(VI) to Cr(III) using reduced graphene oxide/ CuOx composites

A series of rGO/CuOx composites with different doping ratios were synthesized by the alkaline hydrothermal method and used for photoreduction of hexavalent chromium (Cr(VI)) under visible light. The morphology, crystalline structure and surface properties of the composites were analyzed by XRD, BET, FTIR, Raman, SEM, TEM, XPS, and PL characterizations, demonstrating the successful in-situ formation of CuO on the surface of rGO and the formation of heterojunction between rGO and CuO nanoparticles. The rGO/CuO0.3 composite demonstrated superior performance, achieving 100 % adsorption and 97.03 % reduction of Cr(VI) within 10 min under visible light. It also maintained over 83 % removal efficiency after five cycles, highlighting its good stability and reusability. The interfacial transfer and valence changes of Cr(VI) and Cr(III) in direct adsorption and photocatalytic reduction systems were assessed by desorption-dissolution experiments and measurement of Cr(VI) and Cr(III) concentrations in both solid and liquid phases. Based on the results of the inhibitor experiments and the characterization of used rGO/CuO0.3 composite, the photo-reduction mechanisms of Cr(VI) in Vis/rGO/CuO system were elucidated. The results indicated that the reduction of Cr(VI) was driven by the interaction of multiple mechanisms, and the synergistic effect between CuO and rGO significantly improved the photocatalytic activity of the composites. The rGO/CuO0.3 composite manifested great potential as an efficient photocatalyst for Cr(VI) removal, offering a potential pathway for advanced water purification technologies.