Co, Fe co-doped g-C3N4 composites as peroxymonosulfate activators under visible light irradiation for levofloxacin degradation: Characterization, performance and synergy mechanism

To improve the degradation efficiency of g-C3N4 (CN), transition metal elements (Fe and Co) were doped into CN. A novel Co, Fe co-doped CN (Co/Fe-CN) photocatalysts with small size and irregular flake structure were successfully prepared by thermal polymerization of melamine. Co/Fe-CN has a large specific surface area (55.76 m2/g), which provides more adsorption sites and reaction sites for the activation of peroxymonosulfate (PMS). Good visible light response performance (474 nm) and suitable band gap (2.83 eV) ensure that it could be excited by visible light. The active species of •O2-, 1O2, •OH and SO4•- could be stably produced in Co/Fe-CN/Vis/PMS system with appropriate redox potential. Meanwhile, Co and Fe elements doped in CN also could effectively activate PMS and promote the generation of active species. Besides, the continuous generation of photogenerated electrons promoted the cycling of Co3+/Co2+ and Fe3+/Fe2+, and further enhanced the degradation efficiency of Co/Fe-CN/Vis/PMS towards Levofloxacin (LVFX). LVFX could be rapidly removed, reaching 92.1% within 50 min under visible light illumination, and the kinetic rate constant of LVFX was 0.0638 min-1. The quenching experiments verified that the 1O2 was the main active species in the reaction process. The cycling experiments revealed that the Co/Fe-CN/Vis/PMS system had favorable stability and applicability. This work provides a simple preparation method to fabricate bimetallic co-doped CN for the enhancement of degradation rate in the Photocatalyst/Vis/PMS system.