Photocatalytic degradation of tetracycline by N-CQDs modified S-g-C3N4 nanotubes and its product toxicity evaluation

•The S-g-C3N4/N-CQDs composite photocatalyst with hexagonal tubular structure was synthesized by a simple solvothermal method.•The modification of N-CQDs improves the efficiency of charge separation and transfer of S-g-C3N4.•S-g-C3N4/N-CQDs composites showed good photocatalytic degradation efficiency and stability for tetracycline.•S-g-C3N4/N-CQDs composites and tetracycline degradation wastewater showed no biotoxicity to E. coli.