Herein, the preparation of numerous bismuth oxychloride/bismuth oxybromide/bismuth oxyiodide/graphene oxide (BiOxCly/BiOmBrn/BiOpIq/GO) composites is reported. A facile hydrothermal method was employed to synthesize these photocatalysts, which had various GO contents. A total of 10 bismuth-oxyhalide composites were isolated and characterized using FE-SEM, XRD, FE-TEM, UV-Vis-DRS, FT-IR, EPR, HR-XPS, PL, and BET. The photocatalytic efficiencies of these 10 bismuth-oxyhalide composites were measured under visible-light irradiation by estimating the concentration of 2-hydroxybenzoic acid (HBA) degradation. The findings indicated that the rate constant order of the HBA degradations was BiOCl/BiOBr/BiOI/GO > Bi3O4Cl/Bi3O4Br/Bi4O5I2/GO > Bi12O17Cl2/Bi3O4Cl/Bi12O17Br2/Bi7O9I3/GO > Bi12O17Cl2/BiOBr/BiOI/GO > Bi12O17Cl2/Bi12O17Br2/Bi7O9I3/Bi5O7I/GO > Bi3O4Cl/BiOBr/Bi3O4Br/Bi4O5I2 > Bi3O4Cl/BiOBr/BiOI> BiOCl/BiOBr/BiOI > Bi12O17Cl2/Bi5O7Br/Bi5O7I > GO. A maximum rate constant of 0.191 h(-1) was reached for BiOCl/BiOBr/BiOI/GO, providing photocatalytic efficiency that was eight times higher than that of composite BiOCl/BiOBr/BiOI. We also proposed a photocatalytic mechanism demonstrating that O-2(center dot-), h(+/-), (OH)-O-center dot, and O-1(2) are all essential for HBA degradation. (C) 2019 Elsevier Inc. All rights reserved.