The large consumption and discharge of sulfonamide antibiotics has led to the severe aquatic pollution in China.The sulfonamide antibiotic residuals and the resistance genes may pose inestimable threat to human beings and ecosystems.The persulfate-based technology is a potantial process capable of degrading the sulfonamide antibiotics.Considering the above problems,this study aims to develop novel nonradical oxidation processes based on persulfate to realize efficient sulfonamides degradation and illustrate the oxidation mechanism of persulfate nonradical pathways.Theoretical calculations were also adopted to reveal the degradation mechanisms of sulfonamides.The main contents and results are described as follows.To clarify the direct oxidation ability of persulfate,the degradation performances of inactivated persulfate processes(peroxymonosulfate(PMS)alone and peroxydisulfate(PDS)alone)on sulfonamide antibiotics were investigated.The results showed that inactivated PMS could selectively and efficiently degrade sulfonamide antibiotics.When the PMS concentration was 3.25 mmol/L,the sulfonamide antibiotics concentration was 50 mg/L,the pH was 7.5(buffer),and the reaction time was 120 minutes,the degradation efficiency of the six sulfonamide antibiotics were more than 96%,of which the highest was sulfonamide(SDZ)with99%.However,the PDS showed negligible removal efficiency on sulfonamides.Other target pollutants were chosen to verify whether PMS can selectively degrade sulfonamide antibiotics.Then the types and quantities of reactive species in PMS alone system were detected with competitive experiments,scavenging tests and electron paramagnetic resonance(EPR)analysis.These results demonstrated the PMS system involved in the novel nonradical oxidation process might largely contribute to PMS direct oxidation,which led to highly efficient degradation of sulfonamides by PMS alone.In addition,the important factors that influence and stimulate the performance of the PMS alone process,such as PMS dosage,initial SAs concentration,pH and natural inorganic ions,were further investigated.The PMS dosage played critical role in the sulfonamides degradation process by PMS alone,in which the degradation rate of sulfonamides showed linear relation ship with the PMS dosage in the proper range.However,the initial SAs concentration,pH and natural inorganic ions had little influence on sulfonamides degradation,suggesting that PMS alone system had wide adaptability to the environmental change.In view of the low direct oxidation ability of PDS and good characterestics of carbon materials,reduced graphene oxides(rGO)material was selected to activate PDS to enhance the degradation performance of sulfonamide antibiotics.The rGO were prepared from graphite by oxidation-reduction method at different temperature and were characterized by various characterization methods.The results showed that the structure and properties of rGO indicated high potential to activate PDS.The four rGO materials were prelimilarily used in PDS actibation for sulfonamide antibiotics degradation.It was confirmed that the rGO materials had certain adsorption capacity for sulfonamide antibiotics.In addition,the four kinds of rGO materials had good activation ability on PDS.The rGO-700/PDS system was constructed to study the degradation performance of sulfonamide antibiotics.The results showed that rGO-700/PDS system could efficiently degrade sulfonamide antibiotics through both adsorption and activation.When the concentration of PDS was 0.6 mmol/L,the dosage of rGO material was 0.1 g/L,the concentration of sulfonamide antibiotics was 40μmol/L,the initial pH was 5 and the reaction time was 90 min,the degradation efficiency of the six sulfonamide antibiotics were all higher than 90%,of which the highest was sulfathiazole(STZ)at 99.9%.According to the results of quenching experiments and EPR detection,the 1O2 production in the rGO-700/PDS system played an important role in pollutants oxidation.In addition,electrochemical analysis showed that the rGO-700-mediated electron transfer between sulfonamide antibiotics and PDS also contributed greatly to the degradation of sulfonamide antibiotics.Therefore,the rGO-700/PDS system was mainly through the nonradical pathways of both 1O2 oxidation and electron transfer to achieve the efficient degradation of sulfonamide antibiotics.Finally,the mineralization of sulfonamide antibiotic wastewater by rGO-700/PDS system were studied.The highest removal efficiency of TOC was 90.1%,respectively.To analyze the degradation mechanism of sulfonamide antibiotics in the persulfate nonradical oxidation systems,theoretical calculation and experimental determination were combined to propose the possible pathways.Firstly,the properties of six sulfonamide antibiotics were calculated by using Gaussian 09software and DFT method to study the stability and difference between the six sulfonamide antibiotics.Fukui function was selected as descriptor to predict the possible active sites of six sulfonamide antibiotics by PMS direct oxidation.Then the similar pathways and rules of sulfonamide antibiotics degradation in PMS alone system were confirmed and proposed by combining with mass spectrometry.Secondly,the charge distributions of six sulfonamide antibiotics were calculated to predict the active sites in the activation system.The degradation mechanism of six sulfonamides in rGO/PDS system were explored by mass spectrometry. |