Synthesis of novel ZnIn_0.2Ga_1.8O₄/CaIn₂S₄ composite material with S-scheme heterojunction for efficient photocatalytic degradation of organic pollutants and hydrogen evolution

Semiconductor photocatalysts that can both photocatalytic evolve hydrogen from water and degrade organic pollutants are very important to solve the problem of energy shortage and environmental pollution. The S-scheme ZnIn_0.2Ga_1.8O_4/CaIn₂S₄ complex was successfully synthesized using sol–gel and oil bath methods. Characterization technique indicates that chrysanthemum-shaped CaIn₂S₄ is anchored on the surface of irregular nanoparticles ZnIn_0.2Ga_1.8O₄, forming a closely packed heterostructure. The bandgap values of CaIn₂S₄ and Zn(In_0.1Ga_0.9)₂O₄ were determined as 2.11 eV and 3.61 eV, respectively. Under visible-light irradiation, the ZnIn_0.2Ga_1.8O_4/CaIn₂S₄-1(ZC-1) photocatalyst exhibited superior performance in degrading an organic pollutant (RhB) and generating hydrogen compared to ZnGa₂O₄, ZnIn_0.2Ga_1.8O₄, and CaIn₂S₄ alone. The photocatalytic degradation of RhB using ZC-1 was 1.7, 1.31, and 1.14 times higher than that of ZnGa₂O₄, ZnIn_0.2Ga_1.8O₄, and CaIn₂S₄, respectively. Moreover, the photocatalytic hydrogen evolution rate of ZC-1 was 5.8, 3.7, and 13 times higher than that of ZnGa₂O₄, ZnIn_0.2Ga_1.8O₄, and CaIn₂S₄, respectively. The formation of S-type heterojunctions in the composite photocatalysts was confirmed through free radical trapping and electron paramagnetic resonance tests, further enhancing hydrogen production and organic pollutant degradation. This study presents a novel approach for developing ZnGa₂O₄-based composite photocatalysts with S-scheme heterojunctions to address energy shortage and environmental pollution in the future.