Abstract: In this paper, g-C₃N₄ and In₂S₃ were synthesized by thermal polycondensation and hydrothermal method, respectively. In₂S₃/g-C₃N₄ composite photocatalyst was prepared by simple mechanical grinding technology. The crystallographic structure, morphology, microstructure and optical properties of In₂S₃/g-C₃N₄ composite photocatalyst were characterized by X-ray diffraction (XRD), scanning electron microscope(SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR), and UV visible diffuse reflectance spectrum (UV-Vis DRS). The photocatalytic activity was evaluated by degradation of tetracycline (TC) under visible light irradiation. The results show that the In₂S₃/g-C₃N₄ composite photocatalyst with grinding molar ratio of 1∶4 displays the best photocatalytic activity. The observed rate constant of TC degradation under xenon lamp is 0.025 1 min^-1, which is 2.9 times and 1.6 times higher than that of In₂S₃ and g-C₃N₄, respectively. The observed rate constant of TC degradation under natural light is 0.010 4 min^-1, which is 2.6 times and 1.4 times higher than that of In₂S₃ and g-C₃N₄, respectively. The superior photocatalytic performance of In₂S₃/g-C₃N₄ composite photocatalyst is attributed to the efficient migration and separation of charge carriers and the enhanced light absorption capacity. This paper provides a promising approach for designing and developing visible-light-response photocatalysts applied to antibiotic wastewater treatment.

Key words: In₂S₃/g-C₃N₄ composite photocatalyst, mechanical grinding, tetracycline, photocatalysis, In₂S₃, g-C₃N₄