Insight Into The Mechanisms Of BPS And SMX Degradation By Electro-fenton Method Modified By Carbon Cathode

With the rapid development of social economy,the excessive use of endocrine interferons and antibiotics leads to a large number of persistent organic pollutants（POPs）into the environment,resulting in long-term potential harm to the environment,and will cause endocrine disorders and carcinogenic,teratogenic and mutagenic effects.In the existing studies,the removal cost of persistent organic pollutants is high,and easy to produce secondary pollution,which is an urgent problem to be solved.Therefore,some carbon-based catalysts were constructed,which used to electro-Fenton process,and the degradation performance was investigated with bisphenol S（BPS）and sulfamethoxazole（SMX）as the target pollutants.Meanwhile,the degradation mechanism was analyzed by means of liquid chromatography-mass spectrometry（LC-MS）and density functional theory（DFT）.The main results are as follows:（1）Cobalt-based nanoparticles（NPs）on the oxidized carbon black（Co-OBC）was prepared by means of nitrate oxidization,which used for cathode in the study of electro-Fenton.The characterization results showed that Co-OBC presented spherical morphology and the content of C,N,O,Co was evenly distributed.Co-OBC has high mesoporous structure,high hydrophilicity,high content of pyrrole nitrogen and oxygen-containing functional groups,which contributes to 2e^-oxygen reduction.The results of electrochemical performance test showed that the Co-OBC had a better oxygen reduction performance,including the more positive oxygen reduction potential,the onset potential,the half-wave potential and the high limit current density,and the RRDE results showed that the transfer electron number of Co-OBC is closer to 2.Therefore,when Co-OBC as a cathode catalyst for electro-Fenton,BPS can be completely degraded within 15 min,and TOC removal rate of 47.8%within 120 min under the optimal reaction conditions(c(Fe²⁺)=0.3 m M,p H 3,U=-0.5 V).The main active species in the reaction system was determined as·OH by EPR,and the reaction path of BPS attacked by·OH was explored by combining LC-MS with DFT calculation.The toxicity of intermediate products was predicted to be gradually attenuating by ECOSAR.（2）In order to further determine the influence of different types of metals on the degradation performance,Fe-OBC,Mn-OBC,Cu-OBC and Co-OBC catalysts were prepared by the same method.The morphology and structure characterization results showed that the four catalysts appeared spherical,the differences were only metal elements.The electrochemical performance test results showed that all the catalysts had good oxygen reduction performance,and the comparison of performance was as follows:Fe-OBC>Mn-OBC>Cu-OBC>Co-OBC.The SMX degradation performance was judged under c(Fe²⁺)=0.3 m M,p H 3,U=-0.5 V,and the results showed that Mn-OBC had the best degradation performance,which because the existence of Mn atom in three valence states was more conducive to the generation of·OH.Combined DFT calculate with LC-MS was used to detect the intermediates of SMX degradation process,the reaction path was speculated,and the reaction mechanism was studied deeply.（3）Due to the limitations of secondary pollution caused by homogeneous electro-Fenton.In this chapter,Co and Fe co-doped porous carbon（CoFe-NC）were derived from MOFs for the degradation of SMX by heterogeneous electro-Fenton.The morphology characterization results showed that CoFe-NC was the structure of porous carbon,with higher specific surface area and more catalytic active sites,and the results of structural characterization showed that the matching degree of CoFe-NC and Fe₃C was the highest,so the stability of CoFe-NC was very high.Electrochemical characterization results showed that CoFe-NC had a positive oxygen reduction potential,onset potential,half-wave potential and limiting current density,which was more conducive to the occurrence of oxygen reduction reaction.RRDE test results showed that the transfer electron number of CoFe-NC is closer to 2.Therefore,in this study,CoFe-NC was used as the cathode catalyst for the degradation of SMX.The results showed that the removal rate of SMX could reach 91%within 5 h and the degradation efficiency did not decrease significantly after three cycles under the optimal reaction conditions（U=-0.7 V,p H=1）.In summary,the electro-Fenton technology was adopted to degrade POPs in this manuscript.Meanwhile,the degradation mechanism and toxicity of pollutants was analyzed through various means.Then,this study provided a solution to the harm of low-concentration POPs in the environment.