Research On Degradation Mechanism Of Sulfonamides Treated With Advanced Oxidation Processes Based On Density Functional Theory

Sulfonamides（SAs）is a class of antibiotics with the highest detection rate in water.SAs contamination can induce the resistance of natural microorganisms and lead to the emergence of resistance genes.The consequence will then posea serious threat to human health and the balance of ecosystem.Characterized by high stability and complete degradation,Advanced oxidation process（AOPs）demonstrate a broad application prospect in the removal of refractory organic pollutants.Since incomplete mineralization of SAs may lead to the production of highly toxic intermediates,it is of great significance to study the degradation mechanism of SAs degradation in advanced oxidation system.In this study,the research emphasis mainly focused on the degradation mechanism of SAs in Fe（II）-activated persulfate process.SMX was used as the target pollutant to explore the effects of Fe（II）and PS ratio,solution p H value,initial SMX concentration and the addition form of ferrous salt on degradation performance.The optimum reaction conditions for SMX degradation were proposed which was Fe（II）:PS=1:10 undr initial p H with the addition of ferrous salts in solid form.TOC removal extent came to 30%after 240 min of reaction.The reaction stoichiometric efficiency（RSE）was 2.7%.Effects of typical water matrix on SMX removal was also systematically studied.It could be conducted that although these substrates have different degrees of inhibition on SMX degradation,nearly 100%removal of SMX can still realized in 240 minutes with the existence of water matrix.The effectiveness of employing Fe（II）-activated PS system to treat water contaminated by sulfonamides was further confirmed.In order to conduct the dissociation morphology analysis and conformation search,molecular structure of SMX was chosen as the research object.Furthermore,the most stable conformation in thermodynamics was analyzed for weak interaction and the prediction of reaction sites.The wave function analysis showed that N7 was the site with the highest electrophilic reactivity of SMX molecules.Meanwhile,the simultaneous presence of SO₄^·-and·OH in the system was identified by chemical quenching which degradation experiments were carried out under the optimal reaction conditions.UHPLC-HRMS/MS was applied to detect the reaction intermediates of SMX in Fe（II）-activated PS process.Five conversion pathways of SMX were proposed based on theoretical calculation and experimental results.S-N bond cleavage product,amino oxidation product and SEP were detected,indicating that they are the main mechanism of SMX degradation.The log K_ow experimental values of 21 SAs were used as the data set,and the Q-Q plot showed that the data were representative.By using constitutional descriptors and quantum chemical descriptors based on DFT calculation,32 descriptors with significant correlation were screened out by correlation analysis between descriptors and log K_ow.Models were established and then optimized by stepwise multiple linear regression and partial least squares regression,respectively.By comparing the statistical indexes of the obtained models,the optimal model is log K_ow=-2.351+0.113?#ringatoms+0.020?A^--0.005?σ₊²,with statistical parameters p<0.01,F>15,Q²_cum>0.7,and the Y-axis intercept of Q² regression line in permutation test is less than0,which verifies the reliability of the model.