One-step solvothermal synthesis of TiO₂-reduced graphene oxide nanocomposites with enhanced visible light photoreduction of Cr(VI)

Hexavalent chromium, Cr(VI), is a mutagenic and carcinogenic heavy metal environmental pollutant. Photoreduction is one of the remediation methods of the hexavalent chromium Cr(VI), which necessitates design of an efficient catalyst for visible light performance. Here, we report a one-step solvothermal synthesis of TiO₂-reduced graphene oxide (TiO₂-xRGO) composite catalysts using a mild reducing agent, dimethylformamide (DMF). Nanoscale TiO₂ particles in the size range of 4–9 nm were formed on the reduced graphene sheets. The formation of the composite catalysts was accompanied by the appearance of a large fluorescence quenching, which indicates an efficient separation of photogenerated electrons and holes. The composites displayed excellent photoreduction of Cr(VI) in the visible light, which was found to be a function of the weight percentage of RGO in the composite. At the optimum composition of TiO₂-xRGO, a maximum removal rate of 96% was recorded, which was higher than that of the pristine TiO₂, which showed no appreciable catalytic activity under the same condition. The performance degraded with increasing RGO content in the composite, which can be attributed to the higher electron-hole recombination on the RGO surface. The Cr(VI) photoreduction also exhibited a pH dependence. The highest removal rate was observed in the acidic medium.