Efficacy And Mechanism Of Magnetic Biochar Activated Peroxymonosulfate For Treatment Of Antibiotic Wastewater

Fluoroquinolone antibiotics（FQs）are common and hard-to-degrade organic pollutants in the aqueous environment,and their remediation of contaminated water is of great interest.Advanced oxidation processes（SR-AOPs）based on sulfate is considered as a good strategy to treat FQs.Biochar（BC）has a large specific surface area to expose a large number of active sites and thus has an excellent catalytic performance,but biochar-based non-homogeneous catalysts are difficult to recover.Magnetic biochar has excellent catalytic properties and is also easy to separate and recover.In this thesis,magnetic nitrogen-doped biochar（MNBC）,magnetic biochar/cobalt ferrate（MBC/CoFe₂O₄）and magnetic biochar/copper-iron-nickel layered metal oxides（MBC/Cu Fe Ni LDHs）were prepared by co-precipitation and sol-gel methods using magnetic biochar as the substrate material.The comprehensive performance of the catalysts was investigated in terms of physicochemical properties,catalytic performance and stability,and the mechanism of their activation of peroxymonosulfate（PMS）for removing FQs from water was further investigated in depth.MNBC was prepared and optimized by co-precipitation method,and the physicochemical properties of MNBC were analyzed by various characterization.The catalytic performance of MNBC was tested by its effect on activating PMS to degrade ciprofloxacin hydrochloride（CIP）.The results showed that the MNBC composites had more abundant functional groups and porous structures with mesoporous pore size and excellent physicochemical properties compared with the monolithic materials magnetic biochar（MBC）and nitrogen-doped biochar（NBC）.With[catalyst]=0.8 g/L,[PMS]=0.2 g/L,p H=7 and reaction temperature=25℃,the efficiency of CIP degradation by MNBC could reached 92.6%（80 min）,which had excellent catalytic performance.The role of free radicals in the reaction system was further investigated by free radical burst experiments and electron paramagnetic resonance spectroscopy（EPR）.The results showed that the main steps of CIP degradation by the MNBC/PMS system were dominated by free radicals and supplemented by non-radicals.However,the catalytic efficiency of MNBC decreased by 9.2%after four-times resuing,and more fractures appeared on the surface of the material,indicating its structural instability.Therefore,the stability of the catalyst needs to be improved.In order to solve the problem of MNBC catalysts with low stability,the MBC/CoFe₂O₄ catalysts were prepared and optimized by sol-gel method,and the physicochemical properties of MBC/CoFe₂O₄ were analyzed by various characterization.The catalytic performance was tested by its effect on activating PMS to degrade lomefloxacin hydrochloride（LFH）.The results showed that the MBC/CoFe₂O₄ composites had more abundant surface functional groups,more diverse metal valence states,larger specific surface area,and better magnetic properties compared to MBC and CoFe₂O₄.with[catalyst]=0.6 g/L,[PMS]=0.2 g/L,p H=7,and reaction temperature=25°C,MBC/CoFe₂O₄ could degrade 86.9%of LFH in 20min with excellent catalytic performance.In order to further investigate the role of free radicals in the reaction system,it was investigated by free radical bursting experiments and EPR.The results showed that sulfate radicals,hydroxyl radicals,superoxide radicals and singlet oxygen were involved in the degradation process in the reaction system,and sulfate radicals was the main contributor.The LFH degradation efficiency only decreased by 1.5%after five cycles of the reaction,and the physicochemical properties were stable.the MBC/CoFe₂O₄ catalyst solved the problem of poor stability of MNBC catalyst,but the dissolution of highly toxic cobalt ions was high,thus further improvement of the catalyst was needed.In order to further solve the problem of high cobalt ion solubilization with strong toxicity of MBC/CoFe₂O₄,MBC/Cu Fe Ni LDHs（referred to as MC-1）were synthesized by co-precipitation method,and the physicochemical properties of MC-1were analyzed by various characterization.The catalytic performance of MC-1 was tested by its effect on activating PMS to degrade enrofloxacin（ENR）.The results showed that MC-1 composites had more superior physicochemical properties compared to MBC and Cu Fe Ni LDHs,which were block structures with hierarchical surface.With[catalyst]=0.6 g/L,[PMS]=0.4 g/L,p H=7,and reaction temperature=25°C,MC-1 could remove 93.1%of ENR in 60 min with excellent catalytic performance.The role of free radicals in the reaction system was investigated by free radical burst experiments and EPR.The results indicated that the degradation of ENR was dominated by free radicals and assisted by non-radicals.The ENR was degraded mainly by the oxidation and loss of piperazine ring.After cycling the reaction five times,MC-1catalyst still maintained high catalytic performance with stable physicochemical properties and low dissolution of Cu,Fe and Ni metal ions.MC-1 solved the problems of poor stability of MNBC and high dissolution of strongly toxic metals from MBC/CoFe₂O₄,and had good potential for application.