Synergistic adsorption-photocatalytic degradation of tetracycline by S-scheme InVO4/ZnIn2S4 heterojunction: mechanism, toxicity assessment, and potential applications

The development of materials with dual adsorption/photocatalytic functions for the removal of difficult-to-degrade organics is a very promising and challenging strategy. In this paper, a novel S-scheme heterojunction photocatalyst, InVO4/ZnIn2S4, was successfully synthesized with a unique hierarchical structure, which provides plenty of accessible adsorption/photocatalytic sites with a high light-harvesting rate (by multiple reflections). The experimental results show that optimized InVO4/ZnIn2S4 (5-IV/ZIS) has superior removal performance, whose adsorption-photocatalytic synergistic removal of tetracycline (TET) can reach 69.31 % after 15 min and 90.69 % after 45 min. Based on the analysis of the mechanism, the excellent removal performance can be attributed to the adsorption of the target onto the material by hydrogen bonding, followed by the degradation of the adsorbed target by active substances (h+ > O2•− > e- > 1O2 > •OH) generated by the S-scheme heterojunction. In addition, the possible pathways for the photocatalytic removal of TET on 5-IV/ZIS were investigated by HPLC-MS analysis. T.E.S.T. and E. coli inhibition experiments demonstrated a significant reduction in the toxicity of TET after the photocatalytic reaction. In conclusion, the novel multifunctional photocatalyst 5-IV/ZIS prepared in this study can be used for the efficient treatment of organic compounds in wastewater with a bright application prospect.