Catalytic Degradation Of Antibiotics Via Persulfate Activation Over Nitrogen And Sulfur Co-doped Carbon Derived From Chitosan

Persulfate-based advanced oxidation processes（PS-AOPs）was regarded as a promising technology in degrading the emerging pollutants due to its advantages of high efficiency,environmental protection,as well as no secondary pollution.The carbon material serves as a green peroxynitrite catalyst.This is because it contains activated persulfate sites such as jagged edge defects and oxygen-containing functional groups,as well as avoiding the leaching by ions and secondary contamination of metal catalytic materials.However,pure carbon suffered from insufficient catalytic sites and low activation efficiency in activating persulfates.While carbon-based surface defects are effective active sites for catalytic persulfation.Besides,heteroatom doping is an effective strategy for constructing structural defects in carbon materials.Therefore,in our study,nitrogen and sulfur atoms were co-doped into the carbon matrix to optimize the electronic structure and charge density of the carbon network,and to construct structural defects and catalytically active centers,thus improving the catalytic activation of persulfate performance.The specific research contents and conclusions are as follows:（1）S-modified chitosan precursors were synthesized via chitosan and sulfonyl chloride.Then N,S-co-doped carbon materials with excellent dual functions of adsorption and catalysis were synthesized via one-step carbonization.By activating persulfate（PS）,99%of sulfamethoxazole（SMX）was degraded in 90 min,with a mineralization rate of 84%.Compared to the carbon activated PS without sulfur doping(0.0008 min^-1),the rate constant of SMX by carbon after nitrogen and sulfur co-doping was higher by 72-folds(0.0578 min^-1).Thiophene sulfur and structural defects are involved in the activation of PS as the main active sites.During the degradation of SMX,¹O₂ played a major role,SO₄^·-exerted a minor contribution,and O₂^·-acts as the precursor for the production of ¹O₂.Based on the molecular weights of the six degradation products detected by HPLC-MS,six possible SMX degradation pathways were postulated.（2）Chitosan,various rates of N,N-bis（2-hydroxyethyl）-2-aminoethanesulfonic acid sodium,and sodium chloride were used as raw materials to synthesize nitrogen and sulfur doped carbon materials by one-step carbonization method.98%of SMX could be removed by BE-NSC-0.5 activated persulfate within 40 min with k_obs as high as 0.0831 min^-1.On the surface of catalyst,pyridine N,C-OH,thiophene S and structural defects served as active sites for activation of PS,which could generate ¹O₂to degrade SMX directly.It was speculated that there were nine possible degradation pathways for SMX based on the 11 intermediates detected by HPLC-MS.