A magnetically recyclable dual Z-scheme GCNQDs-CoTiO3/CoFe2O4 composite photocatalyst for efficient photocatalytic degradation of oxytetracycline

•Dual Z-scheme GCNQDs/CTO/CFO composite photocatalysts were successfully constructed.•GCNQDs/CTO/CFO composites exhibited good magnetization performance and efficient separation of electron hole pairs.•GCNQDs/CTO/CFO photocatalysts showed excellent photocatalytic performance in oxytetracycline removal.•The pathway and mechanism of oxytetracycline degradation by GCC photocatalysts were proposed. g-C3N4 exhibits excellent performance in photocatalytic degradation of organic pollutants, but the high recombination rate of photogenerated electron-hole pairs limits its application. Herein, a dual Z-scheme g-C3N4 QDs-CoTiO3/CoFe2O4 (GCC) composite photocatalyst was synthesized by in-situ growth method and ultrasonic impregnation method, which effectively increased the separation rate of photogenerated electron-hole pairs and significantly improved the photocatalytic degradation performance. The degradation efficiency of oxytetracycline can reach up to 88% and shows good stability and reusability. At the same time, the GCC composite photocatalyst can be quickly recovered by applying an external magnetic field after the photocatalytic reaction, which reflecting its good magnetic controllability. Furthermore, this work also proposed the possible degradation pathways and degradation mechanisms of the GCC composite photocatalyst to degrade oxytetracycline, which provides efficient way to prepare a low-cost and high-efficiency double Z-scheme heterojunctions.