Catalytic Degradation Of Sulfamethoxazole By Peroxymonosulfate Activation System Composed Of Nitrogen-doped Biochar From Pomelo Peel

Sulfamethoxazole（SMX）is a widely used broad-spectrum antibiotic,which has been detected in many surface water bodies and even drinking water sources.Among the various methods for removing SMX from wastewater,sulfate radical-based advanced oxidation technology has attracted extensive attention due to its great potential in degradation and mineralization of organic pollutants.The selection of catalysts is very important in the peroxymonosulfate（PMS）activation.Carbon-based catalysts have been widely studied due to their low energy consumption,eco-friendless and non-metal ions leaching.However,the preparation process of carbon materials is complex and the raw materials are expensive.The preparation of efficient and stable carbon-based catalysts from low-cost and renewable wastes is still in its early stage.Therefore,it is necessary to further explore the preparation and application of low-cost,efficient and stable carbon-based catalysts.Nitrogen doping is an effective way to improve the catalytic performance of carbon-based materials.Nitrogen doping can not only adjust the electronic structure of the carbon network,but also formed nitrogen configuration can be used as the active site for PMS activation.In this paper,a series of nitrogen-doped biochar were prepared by using agricultural waste pomelo peel as raw material,sodium bicarbonate（Na HCO₃）as pore-forming agent,melamine as nitrogen precursor at different pyrolysis temperatures.Synthesized nitrogen-doped biochar was used for PMS activation to remove SMX.The biochar（C-N-M 1:3:4）prepared under the mass ratio of biomass,Na HCO₃ and melamine 1:3:4 and the pyrolysis temperature 800℃had the best catalytic performance.Under the conditions of C-N-M 1:3:4 dosage of 0.1 g/L,PMS concentration of 0.5 m M,initial SMX concentration of 10 mg/L and p H value of 7,the removal rate of SMX could reach 95%within 30 min.The co-existed H₂PO₄^-,NO₃^-and HCO₃^-in the system have a slight inhibition on the degradation of SMX,while the presence of Cl^-can promote the degradation of SMX.In addition,the 1:3:4 also has high stability and reusability,the removal rate of SMX still reached 80%after four cycles.The activation mechanism of C-N-M 1:3:4/PMS system was deduced by radical quenching experiment,electron paramagnetic resonance（EPR）test and PMS degradation experiment.Non-radical oxidation process based on singlet oxygen（¹O₂）and electron transfer played a major role in SMX degradation.In the process of electron transfer,C-N-M 1:3:4 acted as mediator to transfer electrons from SMX to PMS.Combined with the characterization and analysis,graphitic N,pyrrolic N,carbonyl group（C=O）and the defect may be the active sites for PMS activation.In addition,according to the phytotoxicity experiment,C-N-M 1:3:4/PMS system could effectively degrade SMX,and the toxicity of degradation products were far less than that of the original SMX solution.This study provides new ideas for the followed treatment and utilization of renewable agricultural waste,and also provides a good method for the preparation of nitrogen-doped biochar to remove SMX from wastewater.