Returnable MoS2@carbon nitride nanotube composite hollow spheres drive photo-self-Fenton-PMS system for synergistic catalytic and photocatalytic tetracycline degradation

In this work, we synthesized hollow sphere composites of MoS2@carbon nitride nanotube (MoS2@TCN-S) for in-situ formation of H2O2 under visible light. The photo-self-Fenton system was further coupled with peroxymonosulfate (P-SF-PMS) for promoted reactive oxygen species generation and tetracycline degradation, so that the P-SF-PMS(MoS2@TCN-S) system can remove 94.3 % TC within 120 min, and the removal efficiencies after 15 cycles decrease by less than 5 %. The P-SF-PMS(MoS2@TCN-S) system also shows excellent degradation performance for actual wastewater, with COD removal rates of domestic sewage and secondary sedimentation tank effluent reaching 64.6 % and 58.7 % within 120 min. Quenching experiment and ESR results reveal the synergy of PMS and P-SF system, which was the key to improving the degradability and pH (3–9) adaptability of the P-SF-PMS system. Under alkaline conditions, PMS and H2O2 generated on MoS2@TCN-S activate each other and form 1O2 and OH, which solves the problem of poor degradation of P-SF system under alkaline conditions. Under acidic and neutral conditions, O2– becomes the main ROS, the activation of PMS by O2– and the synergistic effect of PMS and H2O2 make the P-SF-PMS system get rid of the dependence on H+. In addition, direct Z-scheme heterojunction enables MoS2@TCN-S to exhibit faster electron transfer ability, faster H2O2 generation ability, stronger adsorption capacity for PMS, and lower activation barrier for *HSO5, which also enhances the synergistic effect between PMS and P-SF system. In this study, a new type of multi-functional water purification material is proposed, and the synergism of PMS and P-SF system is revealed.