| In recent years,Advanced Oxidation Process(AOPs)based on persulfate(PS)has been extensively studied and used for soil and wastewater remediation.Compared with the disadvantages of high energy consumption for thermal activation and harsh conditions of photocatalytic,solid heterogeneous catalyst activated PS has gradually become a research hotspot due to its low energy consumption and strong effect.In this paper,with self-made supported biochar as catalyst and tetracycline(TC)as target pollutant,the activation pathway of different types of biochar for PS was studied,and the degradation mechanism of TC was analyzed preliminarily.The main research results are as follows:(1)The nitrogen and copper co-doped biochar(N-Cu/BC)was prepared and applied to activate PS to degrade TC in water.The results showed that compared with N or Cu doping alone,co-doped biochar had the best catalytic effect.Under the optimal conditions,20 mg/L of TC could be completely removed within 90 min.This system had the advantages of low demand for PS,high catalytic effect,wide application range of p H and strong anti-interference ability,etc.High concentration of chlorine ions and bicarbonate ions had little impact on the degradation of pollutants.By means of quenching experiment,EPR detection and residual PS concentration determination,two possible reaction pathways about radical pathway and nonradical pathway were proposed,and the radical pathway was the dominant one.Under the radical pathway,the copper substance on the surface of the material activated PS to generate hydroxyl radicals(HO·),and the HO· directly reacted with the pollutants to generate a series of intermediate products and even directly mineralized TC.However,due to the loss of copper,the catalytic performance of the material decreased after repeated use.Under the non-radical pathway,the TC adsorbed on the material surface was directly degraded by electron transfer with PS.The intermediate products of the reaction system were analyzed by LC-MS,the main intermediate products of P2 and P7 were formed and two main conversion routes were proposed.(2)The nitrogen-doping biochar material(N-BC)was successfully prepared by using thiourea as a nitrogen precursor and straw as biomass through sufficient grinding and pyrolysis.The biochar was applied to activate PS to degrade TC in water and the effect and mechanism of nitrogen doping on PS activation of biochar were investigated.Compared with the biochar supported transition metal catalyst in part 1,it needed higher concentration of PS and longer reaction time to completely remove 20 mg/L of TC in the nitrogen-doped biochar system,but it can effectively avoid secondary pollution.The SEM results showed the biochar has obvious pore structured.The specific surface area of biochar at different pyrolysis temperature was studied by BET,it was found that pyrolysis temperature played a key role in the specific surface area of the material,while nitrogen doping played a little role.The influence of nitrogen doping on the structure of biochar was studied by XPS and Raman,it was found that nitrogen doping could increase the graphite nitrogen content in biochar,the defect edge of the material increased and further form the graphitization structure,and enhanced the catalytic performance of the material.Therefore,the catalytic performance of the material was mainly attributed to the graphitization carbon structure caused by nitrogen doping.The results of quenching experiments,EPR detection and electrochemical experiments showed that the removal of TC by N-BC/PS system mainly depended on the electron transfer between pollutants and PS,while the effect of free radicals was not significant.In general,the NCu/BC/PS system was dominated by free radical pathway,while the N-BC/PS system was dominated by non-radical pathway. |
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