The Influence Of Soluble Components In Water Environment On The Photochemical Conversion Of Sulfamethazine

Sulfonamides?SAs?are ubiquitous in natural water environments,They have attracted much attention due to their ecological toxicology,the induction of bacterial flora resistance and the generation of resistance genes and other ecological effects.Photochemical conversion is the main conversion pathway of antibiotics in the water environment,and is significantly affected by the dissolved components.At present,extensive research has focused on the effects of single dissolved components on the photochemical conversion of SAs,while the multiple dissolved components in the actual water environment coexist,the effect of dissolved components on the multi-component complex effect of SAs photodegradation at ambient concentration levels is unclear.In this study,sulfamethazine was selected as the research object,and the four common dissolved components:dissolved organic matter?DOM?,NO₃^-,HCO₃^-and Cu²⁺in the water environment were selected.The combined effects of four dissolved components on the photodegradation of sulfamethazine were studied,and the mechanism of the effect of solubility combination on the photodegradation of sulfamethazine was studied.The main research contents and results are as follows:?1?The composite effect of the four dissolved components of DOM,NO₃^-,HCO₃^-and Cu²⁺on the photolysis kinetics of sulfamethazine was studied by response surface methodology.The experimental results show that significant level of p<0.05,the single dissolved components DOM,HCO₃^-and Cu²⁺can significantly promote the photodegradation of sulfamethazine;DOM-DOM and HCO₃^--HCO₃^-interactions have significant inhibitory effects on the photodegradation of sulfamethazine.The Cu²⁺-DOM interaction is significant at the 90%confidence level and contributes to the photodegradation of sulfamethazine.?2?The mechanism of the effect of DOM on the photodegradation of sulfamethazine was studied by laser flash photolysis?LFP?experiment and free radical quenching experiments.The results show that the high reactivity of ³DOM^*with sulfamethazine promotes photodegradation,and the degradation reaction is caused by electron transfer between ³DOM^*and sulfamethazine.The inhibition of the DOM-DOM interaction is due to the ground state DOM quenching ³DOM^*or the oxidation intermediation of sulfamethazine induced by ³DOM^*can be quenched by DOM.?3?The mechanism of the interaction between Cu²⁺and Cu²⁺-DOM on the photodegradation of sulfamethazine was studied by free radical quenching experiments.The results showed that sulfamethazine could form a complex with Cu²⁺,which enhanced the photo-activity of sulfamethazine and increased the quantum yield,then promoted the photodegradation of sulfamethazine.Irradiation from sunlight can cause electron transfer from DOM-Cu²⁺to O₂ to form·OH,thereby promoting the photodegradation of sulfamethazine.?4?The mechanism of photodegradation of sulfamethazine by HCO₃^-was studied by LFP and steady-state photolysis experiments.The results showed that HCO₃^-was easily oxidized by triple-excited sulfamethazine to produce carbonate radical anion?CO₃·^-?,it was found that CO₃·^-and sulfamethazine have high reactivity(secondary rate constant was 2.2×10⁸ L·mol^-1·s^-1)by LFP,so HCO₃^-has a promoting effect on photodegradation of sulfamethazine.The inhibition of photodegradation of sulfamethazine by HCO₃^--HCO₃^-interaction is attributable to the quenching of CO₃·^-by HCO₃^-.?5?The photolysis products of sulfamethazine was determined by HPLC-MS-MS in the presence of DOM or HCO₃^-.Degradation pathway analysis shows that sulfamethazine produces corresponding photolysis products mainly through the two methods of hydroxylation and desulfonation in the presence of DOM or HCO₃^-.