N and S co-doping of TiO2@C derived from in situ oxidation of Ti3C2 MXene for efficient persulfate activation and sulfamethoxazole degradation under visible light

Visible-light-driven photocatalysts with synergistic persulfate (PS) activation and photocatalysis possess enormous pollution-control potential. Herein, nitrogen and sulphur co-doped TiO2@C hybrid (N/S-TiO2@C) featuring the complementary visible-light photocatalysis and synergetic PS activation was synthesized by in situ oxidation of Ti3C2 MXene and thereafter co-doping with N and S. Both anatase and rutile phases of TiO2 were attained in N/S-TiO2@C. The decrease of TiO2 bandgap (about 1.81 eV) and the defect of carbon layer caused by the N and S co-doping in both TiO2 crystal and carbon layer enabled the synergistic enhancement of PS activation and photocatalysis. Complete degradation and 93.4% mineralization of sulfamethoxazole (SMZ, 10 mg/L) were achieved by dosing PS (2 mM) and N/S-TiO2@C (0.4 g/L) under visible light within 30 min. The degradation rate by N/S-TiO2@C through PS activation under visible light was 27.9-, 11.1-, and 2.30-fold higher than that by PS, N-TiO2@C, and S-TiO2@C alone, respectively. Reactive species SO4−,1O2, OH, and O2−, especially the former two, were determined dominating the SMZ degradation, and the degradation pathways were illustrated through intermediates identification. Moreover, N/S-TiO2@C kept excellent performance in activating PS to degrade SMZ in real water samples. These results indicate that N/S-TiO2@C is a stable and promising PS activator under visible light and has a good application potential in organic wastewater treatment.