Peroxymonosulfate Activation By Modified Graphite Carbon Nitride Under Visible Light For Degradation Of Sulfamethazine

Sulfonamides（SAs）are ubiquitous in the water environment,posing a potential threat to human health and ecological environment.Visible light photocatalysis combined with peroxymonosulfate oxidation technology（Vis/PMS）has attracted wide attention.Graphite carbon nitride（g-C₃N₄）,as an efficient and stable photocatalyst in the process of synergistic oxidation,can quickly respond to visible light and promote the degradation of SAs.In this study,melamine,oxalic acid and metal chloride were used as raw materials to prepare a variety of modified g-C₃N₄-based catalysts,and the best catalysts were applied to the degradation of sulfamethazine（SMZ）by visible light photocatalysis and peroxymonosulfate oxidation.By investigating the degradation effect and influencing factors of SMZ by g-C₃N₄-based catalysts,the degradation mechanism of SMZ was preliminarily analyzed,which provided a theoretical basis for the development of g-C₃N₄-based photocatalyst capable of efficiently degrading SAs.A variety of g-C₃N₄-based catalysts（g-C₃N₄,O-g-C₃N₄,Co-g-C₃N₄,M-O-g-C₃N₄）were prepared by high-temperature calcination method,and the best catalysts were selected through characterization test and degradation effect analysis.In Vis system,the photocatalytic activity of Ce-O-g-C₃N₄ is the highest,and the degradation rate of 5mg/L SMZ is 85%.In Vis/PMS system,5 wt.%Co-O-g-C₃N₄ has the highest photocatalytic activity and can completely degrade 10 mg/L SMZ in 20min.The characterization results show that the modified Co-O-g-C₃N₄ catalyst has similar morphology and structure to that of g-C₃N₄,the specific surface area of Co-O-g-C₃N₄ increases to 15.079 m²/g,the band gap decreases to 1.40 e V,and the photocatalytic performance is improved.The factors affecting the treatment effect of Co-O-g-C₃N₄/PMS/Vis system were studied.When the initial p H is 11,the dosage of catalyst and PMS is 50 mg/L and 0.3g/L,respectively,the degradation rate of 10 mg/L SMZ can reach more than 98%in10 min.Inorganic anions NO₃^-,HCO₃^-and Cl^-can inhibit the degradation of SMZ,while HPO₄^2-can promote it.The catalyst can completely degrade 10 mg/L SMZ under different water quality background conditions（deionized water,clear river water,reclaimed water plant effluent）,and it is universal for the degradation of many antibiotics（SMZ,CBZ,SMX,SMR,CLX）.The degradation rate can reach 71.28%after repeated use for four times,and the catalyst has good stability.The mechanism of Co-O-g-C₃N₄/Vis/PMS degradation of SMZ was preliminarily discussed.The free radical capture experiment and EPR test show that·OH、SO₄^·-、¹O₂、O₂^·-and h⁺are active species in the degradation process of SMZ.According to the results of HPLC-MS test,four degradation paths of SMZ are inferred.On this basis,the mechanism of Co-O-g-C₃N₄ activating PMS to degrade SMZ under visible light is expounded.