Degradation Of Sulfadiazine By Persulfate Catalyzed By Sulfidated ZVI : Performance And Mechanism

As a common antibiotic,sulfadiazine is widely used in human medical and livestock diseases due to its low price and stable effect.The sulfadiazine detected in water and soil is not only toxic to organisms,but also can induce the generation of resistance genes,thus posing a potential threat to the stability of the ecosystem.In this study,micron zero-valent iron（mZVI）was vulcanized by ball milling to prepare sulfurized zero-valent iron（S-mZVI）for activation of persulfate（PDS）to degrade sulfadiazine（SDZ）.The effects of initial pH value,persulfate concentration and concentration of mZVI and S-mZVI on the degradation of sulfadiazine in mZVI/PDS system and S-mZVI/PDS system were investigated.The optimal performance parameters were obtained:the initial pH of the solution was 4.0,the initial concentration of zero-valent iron was 56 mg/L,and the initial concentration of persulfate was 0.5 mmol/L.The effects of different anions（sulfate ions,chloride ions and nitrate ions）on the two systems were investigated,and the effects of the vulcanization process on the zero-valent iron activated persulfate system at different concentrations of anions were investigated.Combined with chemical quenching experiments and EPR spectroscopy,the active species in the reaction system were analyzed,supplemented by quantum chemical calculations,the possible reaction sites were calculated,and the intermediate products produced during the reaction were detected by mass spectrometry,and the possible reaction pathways were speculated.When the initial pH value is 3.0,the sulfurization treatment does not enhance the effectiveness of zero-valent iron-activated persulfate degradation of sulfadiazine.However,when the initial pH value is in the range of 4.0-9.0,the performance of the S-mZVI/PDS system for degrading sulfadiazine is significantly better than that of the mZVI/PDS system.When the initial concentration of zero-valent iron is 5.6mg/L to 112 mg/L,and the initial concentration of persulfate is in the range of 0.1mmol/L to 2 mmol/L,the effectiveness of S-mZVI/PDS system for degrading sulfadiazine is Better than the mZVI/PDS system.The performance experiment determined that the optimal experimental parameters were initial pH of the solution of 4.0,initial concentration of zero-valent iron of 56 mg/L,and initial concentration of persulfate of 0.5 mmol/L.Sulfate ions and chloride ions can strengthen the corrosion of zero-valent iron surface and reduce the difference in the efficiency of S-mZVI/PDS and mZVI/PDS removal of sulfadiazine.However,in the presence of different concentrations of nitrate ions,vulcanization can always strengthen mZVI/PDS system degrades the efficacy of sulfadiazine.The quenching experiment and EPR experiment proved that the main oxide species in the S-mZVI/PDS system was·SO₄^-,and·SO₄^-production in the S-mZVI/PDS system was higher than that in the mZVI/PDS system.The molecular structure of sulfadiazine was calculated and optimized by density functional theory（DFT）in quantum chemical calculation.The charge distribution and CDD value of the atom were obtained,and the possible reaction sites in the sulfadiazine molecule were determined to be 7S and 14C.From the results of mass spectrometry,it can be seen that·SO₄^-completes the degradation of sulfadiazine mainly by attacking the S-N bond of sulfadiazine and the-NH₂ group.