Self-Assembled Reduced Graphene Oxide-TiO₂ Thin Film for the Enhanced Photocatalytic Reduction of Cr(VI) Under Simulated Solar Irradiation.

In this study, reduced graphene oxide-TiO₂ (RGO-TiO₂) thin film was prepared by a simple self-assembly method at the gas/liquid interface. The as-prepared thin films were characterized by X-ray diffraction (XRD), Raman spectra, scanning electron microscopy (SEM), UV-visible-diffuse reflectance spectroscopy (UV-vis-DRS) and X-ray photoelectron spectroscopy (XPS). Photocatalytic activities of TiO₂ and RGO-TiO₂ thin film were investigated via the reduction of Cr(VI) under simulated solar light and visible light (λ > 420 nm) irradiation. The results showed that the RGO-TiO₂ thin film exhibited remarkably enhanced activity for photoreduction of Cr(VI) under simulated sunlight or visible light irradiation, with a reaction rate constant of 5.7 times greater than that of pure TiO₂ thin film. The main reason for enhanced photocatalytic activity is that introduction of RGO can restrain the recombination of photogenerated electron-hole pairs and reduce the aggregation of TiO₂ NPs. The effects of different reaction parameters such as irradiation time, irradiation source, pH values, catalyst dosage and initial Cr(VI) concentration were investigated in detail. The highest photoreduction efficiency of Cr(VI) was achieved and the reduction rate constant k was 0.0189 min-1 during the reduction of 0.5 mg L-1 of Cr(VI) with 10 cm² RGO-TiO₂ thin film at pH 2.0 and 293 K. Moreover, different scavengers were also added in the photoreduction of Cr(VI) system to identify the reactive species. Based on the results of the present study, a possible mechanism of photoreduction on RGO-TiO₂ thin film under simulated solar light was proposed. Overall, this study provides a novel approach to efficiently photoreduction of Cr(VI) by RGO-TiO₂ thin film.