BACKGROUND The formation of heterojunction is an effective mean for increasing the photocatalytic activity of single-phase semiconductor photocatalyst. RESULTS In this report, KNbO3/N-defected g-C3N4 (KNO/CNx) composites were prepared by an impregnation heat method. The optimized photocatalyst 3% KNO/CNx possesses excellent photocatalytic activity (100 mL, 10 mg/L; 84% degradation within 120 min) in the degradation of tetracycline (TC) under visible light (lambda > 420 nm), and it can reach about 125, 10.71 and 3.75 times the degradation kinetic constants, compared with KNO, CN, and CNx, respectively. Furthermore, 3% KNO/CNx possesses relatively high stability during the entire photoreaction process. CONCLUSION This enhanced photocatalytic activity of KNO/CNx is mainly ascribed to the synergistic effect between the heterojunction and defect engineering, which expand the visible-light adsorption and accelerate the separation efficiency of photo-induced electron-hole pairs. The research is expected to be used to improve the structure and properties of KNO-based composites, which provides a possibility for practical application of environmental restoration. (c) 2020 Society of Chemical Industry