Efficient visible light-driven core-shell-structured ZnS@Ag2S nanoparticles-anchored reduced graphene oxide for the reduction of Cr(vi)

A ZnS@Ag2S/RGO nanocomposite with high catalytic efficiency was synthesizedviahydrothermal method usingl-cysteine as the sulfur source. The morphology, crystal structure, and surface chemistry of ZnS@Ag2S/RGO was characterized by UV-Vis, X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), Raman, and photoluminescence (PL). The TEM image shows core-shell ZnS@Ag2S nanoparticles uniformly distributed on RGO sheets. The photocatalytic activity of ZnS@Ag2S/RGO was evaluated by the reduction of Cr(vi) under visible light irradiation. ZnS@Ag2S/RGO showed higher activity in Cr(vi) reduction compared to ZnS@Ag2S and ZnS under similar conditions. The superior photocatalytic activity of ZnS@Ag2S/RGO was ascribed to the more efficient separation/transfer of charge carriers as well as the enhanced visible light harvesting. The effect of the amount of catalyst, pH, and Cr(vi) concentration on the reduction efficiency of the nanocomposite was investigated. This study showed that the complete reduction of Cr(vi) in the presence of ZnS@Ag2S/RGO occurs within a short exposure time of as low as 40 min at optimized conditions.