Effect Of Biochar-modified Cathode On The Degradation Process Of Sulfonamide Antibiotics Through Electro-fenton

Antibiotics,as a common antibacterial drug,are widely used in the treatment of a variety of diseases.In recent years,China has become one of the countries with the largest production and employment of antibiotics.However,the subsequent misuse and abuse of antibiotics have caused serious environmental pollution.In order to reduce the impact of sulfonamides,one of the most widespread antibiotic residues in the environment,and to find a suitable route for the ecological treatment and disposal of Taihu blue algae,a pollutant that seriously affects the aquatic ecological environment nearby Wuxi city,China.Algal biochar materials were prepared by pyrolysis of Taihu blue algae at high temperature under anaerobic conditions.The surface structure and functional groups of algal biochar were improved with the adding of activator,then the electrode was prepared by biochar coating to construct the electro-Fenton（EF）system.Expectedly,biochar coated cathode can effectively degrade Sulfadiazine（SDZ）,a type of widely implemented sulfonamide antibiotic,aiming to achieve efficient degradation and mineralization.In addition,degradation products were examined and the changes in their ecotoxicity were assessed.The main conclusions are as follows:（1）The activated algal biochar material A-BC600 was prepared with Taihu blue algae as biomass material and activator at 600℃,with a specific surface area of 1361.2 m²/g and an average pore diameter of 2.097 nm.It was confirmed by X-ray photoelectron spectroscopy（XPS）that it had a highly-content pyridine N structure.Also,its good electrochemical properties were verified by cyclic voltammetry（CV）,electrochemical impedance spectroscopy（EIS）and other electrochemical means.Moreover,capability of producing H₂O₂by 2-electron oxygen reduction reaction was verified by Electrocatalysis experiment,and the accumulation amount can reach about three times of the bare steel electrode in the same time.（2）A-BC600 modified cathode was prepared through the coating with polyvinylidene difluoride（PVDF）,and an EF system was constructed to degrade sulfadiazine.The generation of ·OH was verified by electron paramagnetic resonance（EPR）.The optimal experimental parameters were determined by single factor experiment as:p H at 3,50 m M Na₂SO₄as electrolyte,current density of 20 m A/cm²,and the removal rate of SDZ exceeded96%after 240 min of degradation.Notedly,after four repeated recycling using the modified cathode,the removal rate can still be maintained at more than 96%.（3）The molecular structure of SDZ was optimized by density functional theory（DFT）calculation.Combined with Fukui function and frontier orbital theory,the free radical attack sites of SDZ were predicted,and 19 of SDZ possible degradative intermediates were speculated.According to the prediction of free radical attack sites,the 19 of predicted degradative intermediates were summarized into four propable degradation paths.（4）Through the simulation of SDZ intermediate products on each degradation path by ecological structure activity relationship（Eco SAR）and Toxicity Estimation Software Tool（T.E.S.T.）,the biotoxicity and bioconcentration factors of most of the end products of each degradation pathway were lower than those of SDZ.It seems that the EF system constructed by biochar-modified cathode can effectively degrade SDZ.Thereby avoided the toxic effect of its intermediates on organisms,and finally reduced its enrichment in organisms.