Microwave synthesis of ZnIn2S4/WS2 composites for photocatalytic hydrogen production and hexavalent chromium reduction

Abstract

A rapid microwave synthesis route for the fabrication of ZnIn₂S₄ powder and ZnIn₂S₄/WS₂ composites is presented. Firstly, the effects of different sulfur sources – thioacetamide and L-cysteine – on the physicochemical properties and photocatalytic H₂ production of the synthesized ZnIn₂S₄ were investigated. It was found that well-defined flower-like ZnIn₂S₄ microspheres obtained from L-cysteine facilitated a relatively higher H₂ production rate. Then, different loadings of WS₂ were introduced into the well-defined flower-like ZnIn₂S₄ microspheres aiming to improve its photocatalytic H₂ production. Compared to pure ZnIn₂S₄ and WS₂, all ZnIn₂S₄/WS₂ composite photocatalysts exhibited enhanced photocatalytic H₂ production in the presence of Na₂S/Na₂SO₃ as sacrificial reagents under UV-visible irradiation, where the ZnIn₂S₄/WS₂-40% wt composite had the highest photocatalytic activity. For this material, 293.3 and 76.6 μmol h⁻¹ g⁻¹ of H₂ gas were produced under UV-visible and visible light irradiation, respectively. In addition, the photoreduction activity of hexavalent chromium (Cr(VI)) by ZnIn₂S₄/WS₂-40% wt was also investigated under visible light irradiation and it was observed that 98.5% of Cr(VI) was reduced within 90 min at pH 4.