Preparation of ZnIn2S4 nanosheet-coated CdS nanorod heterostructures for efficient photocatalytic reduction of Cr(VI)

Nowadays, hexavalent chromium (Cr(VI)) in wastewater seriously threatens ecological systems and human health due to its acute toxicity and potential carcinogenicity. Simultaneously, semiconductor photocatalytic reduction is gaining increasing significant research attention in the treatment of Cr(VI). Hence, three-dimensional (3D) ZnIn2S4/CdS composite photocatalysts, assembled by 1D CdS nanorods and 2D ZnIn2S4 nanosheets, were prepared via a hydrothermal method for reduction of Cr(VI). The composition, microstructure, surface elements and optical properties of the ZnIn2S4/CdS composites were thoroughly characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy. The as-prepared ZnIn2S4/CdS composites showed higher photocatalytic activity for reduction of Cr(VI) compared with pure CdS and ZnIn2S4 under visible light irradiation. Meanwhile, the ZnIn2S4/CdS composite with a mole ratio of 0.33:1 displayed the best photocatalytic activity, with the efficiency for reduction of Cr(VI) (50 mg/L) reaching 100% within 30 min. The 3D heterostructure not only provided a large surface area, but also effectively separated photogenerated electrons and holes. Importantly, the structure and activity of the catalyst were maintained after three cycles, showing its superior stability. The photocatalytic mechanism of the as-prepared composites was also discussed in detail.