Anchoring SrTiO₃ nanoparticles on layered ZnIn₂S₄ to construct S-scheme heterojunctions as novel photocatalysts for efficient degradation of MO dye

Water pollution can be efficiently treated by semiconductor photocatalysts under sunlight irradiation. In this study, novel S-scheme SrTiO₃/ZnIn₂S₄ composites were successfully fabricated via a facile oil-bath method. And the synthesized samples were then characterized by various characterization techniques together with Density Functional Theory (DFT) calculation. The X-Ray Diffraction(XRD)patterns show that SrTiO₃/ZnIn₂S₄ composites are composed of cubic perovskite structure SrTiO₃ and hexagonal phase ZnIn₂S₄. The High Resolution Transmission Electron Microscope(HRTEM)and Field Emission Scanning Electron Microscope (FESEM) images showed the intimate contacts between SrTiO₃ and ZnIn₂S₄ are established to form the heterojunction. The photocatalytic activity of the composite was excellent when degrading organic pollutants, which outperformed that of pristine SrTiO₃ and ZnIn₂S₄. The prepared SrTiO₃/ZnIn₂S₄-33% composite sample was proved to have the best photocatalytic activity, with 98 % degradation of organic pollutants under 32 min. The ·O₂^– is the main active reaction species for the degradation of organic pollutants, which was demonstrated by free radical trapping experiment. In addition, the mineralization of organic pollutants during the degradation process was analyzed by Total Organic Carbon (TOC) test. According to a series of experimental and theoretical calculations, the S-scheme heterojunction formed in the SrTiO₃/ZnIn₂S₄ composite is put forward for comprehending the photocatalytic degradation of organic pollutants and the formation of free radicals.