Mechanism Of Pyrite-biochar In Persulfate Activation For Sulfamethoxazole Degradation

In recent years,the abuse of sulfonamide antibiotics has seriously threatened the ecosystem and human health,and persulfate oxidation is an effective means to degrade sulfonamide antibiotics.However,in conventional persulfate oxidation process,the persulfate is usually consumed due to side reactions such as radical recombination,leading to a decrease in the mineralization of the target contaminant.The successive non-radical and radical process is an emerging technology for efficient degradation and enhance mineralization of organic pollutants,where peroxynitrite activation is the key to enhance the mineralization of the target pollutant.Biochar is widely used in the activation of persulfate because of its simple preparation and abundant source,but the normal biochar has low catalytic activity and poor ability to mineralize organic pollutants.In this paper,reed biochar was modified and loaded with pyrite to produce composites,sulfamethoxazole was chosen as the target contaminant,and the effects and mechanisms of action of the modified composites were investigated in the continuous non-radical and radical oxidation of sulfamethoxazole systems based on persulfate.The results of the study can provide new ideas and theoretical basis for the system to improve the mineralization of the target pollutants.The specific results of the study are as follows:（1）The biochar composites with different pyrolysis temperatures and pyrite composite ratios were subjected to sulfamethoxazole degradation experiments,and the optimal preparation conditions were screened.The results showed that the pyrite-biochar composite（600MRSC₁）had the optimal performance of actived peroxymetho-xazole（PMS）for the degradation of sulfamethoxazole（SMX）.The pseudo first-order reaction kinetic constants is 0.0327 min^-1,which was much higher than that of the pristine biochar without the pyrite composite.（2）By applying 600MRSC₁ to the successive non-radical and radical process（SNRP）based on PMS,and exploring the optimal reaction conditions of this process.The SNRP-600MRSC₁system was found to be most effective in degrading SMX when the 600MRSC₁addition was 0.5 g/L,the PMS concentration was 1.5 m M,the SMX concentration was 10 mg/L,and the pH of the reaction solution was 7.Compared with the 600MRSC₁/PMS system,the mineralization of SMX in the SNRP-600MRSC₁system was increased to 72.8%.（3）The free radical quenching experiments,EPR tests and probe compound experiments demonstrated that the SNRP-600MRSC₁ system had no free radical generation in the first phase and the mechanism of SMX degradation was direct oxidation by PMS.The results of tert-butanol,ethanol and L-histidine quenching experiments showed that SO₄^·-,·OH and ¹O₂ were generated in the second phase of SNRP-600MRSC₁ system,and this conclusion was further confirmed by EPR spectroscopy and benzoic acid and phenol probe experiments.The results of competitive kinetic experiments using nitrobenzene,benzoic acid,furfuryl alcohol and SMX respectively showed that SO₄^·-dominated the second phase of the SNRP-600MRSC₁ system,accounting for 41.22%.The XPS spectra before and after the600MRSC₁ reaction indicated that Fe（Ⅱ）on the composite surface was the catalytic active site,and the loaded pyrite was oxidized to retard the release of Fe²⁺.The Fe²⁺/Fe³⁺cycle existed in the SNRP-600MRSC₁ system,and the sulfur species in the composite accelerated the Fe²⁺/Fe³⁺cycle so that the PMS in the system can be effectively utilized.The intermediates of SMX were measured by LC-MS and the possible degradation pathways were deduced.The results showed that SMX generated intermediates by hydroxylation in the first phase of SNRP-600MRSC1 system,and then the intermediates were attacked by SO₄^·-,·OH and other reactive substances.resulting in ring opening or oxidation of the isoxazole ring and S-N bond breakage.（4）To investigate the effects of Cl^-,NO₃^-,HCO₃^-and humic acid（HA）on the degradation of SMX by SNRP-600MRSC₁ system,the results showed that Cl^-,NO₃^-,HCO₃^-,HA had no significant inhibition on the degradation of SMX.In the river water or tap water,the SNRP-600MRSC₁ system degraded SMX better than the pure water system,which indicated that the SNRP-600MRSC₁ system was resistant to environme-ntal disturbance factors.The stability and reusability of 600MRSC1 catalyst were excellent,and the SMX degradation rate after 5 cycles was a remarkable 93.7%.