The Degradation Of Organic Pollutants In Water By Fe-mn Binary Oxides Modified Biochar-based Fenton-like Reaction And Mechanism Study

Biochar,a low-cost and carbon-rich porous substance produced by pyrolysis of various waste biomass,has the characteristics of rich functional group and well-developed pore structure.Meanwhile,biochar is capable of catalyzing H₂O₂because of persistent free radicals（PFRs）.Using biochar as heterogeneous Fenton-like catalyst can overcome some drawbacks of homogeneous Fenton reaction such as limited working p H range and generation of iron sludge.However,PFRs existed on biochar surface cannot be regenerated,limiting the catalytic capacity of biochar,and biochar is also difficult to recover from wastewater.Recent studies have reported that chemical modification can dramatically enhance catalytic activity of biochar.Hence,in this study,Fe-Mn binary oxides modified biochar（FeMn/biochar）was fabricated via impregnation-calcination method and used as heterogeneous Fenton-like catalyst to degrade organic contaminants such as polycyclic aromatic hydrocarbons（PAHs）,dyes,and antibiotics.Meanwhile,the impacts of visible light irradiation and reducing agents on catalyst activity and·OH yield were also investigated.Results of SEM,BET,XRD and FTIR suggested that Fe-Mn binary oxides were bounded to the surface of biochar via interacting with-OH and-COOH,and biochar obviously prevented the aggregation of Fe-Mn binary oxides.Besides,ESR results indicated that metal treatment can also promote the generation of PFRs.FeMn/biochar-H₂O₂photo-Fenton system can remove 82.2%of naphthalene within 148min When catalyst dosage and H₂O₂dosage was 1.0 g/L and 150 m M,respectively.XPS measurement and PFRs quenching experiment showed that surface Fe（II）,Mn（II）and PFRs existed on FeMn/biochar were involved in the activation of H₂O₂.The prominent degradation efficacy of naphthalene was ascribed to the following reasons:（I）the synergy effects of Fe-Mn binary oxides and biochar benefitted generation of PFR and alleviated aggregation of Fe-Mn binary oxides,which not only increased the amount of active sites,but also increased access of H2O2 and naphthalene to active sites on FeMn/biochar surface;（II）the synergy effects of Fe and Mn can effectively control the decomposition rate of H₂O₂and increase the amount of·OH;（III）visible light irradiation promoted Fe（III）/Fe（II）cycle,which was beneficial for the regeneration of Fe（II）.Moreover,FeMn/biochar showed good stability and reusability during photo-Fenton process and this FeMn/biochar/H₂O₂photo-Fenton system can work effectively at a wide p H range.In addition,systematic assessment of reducing agents（RAs）effects on FeMn/bochar-H2O2 process suggested that RAs can affect performance of heterogeneous Fenton-like system from diverse aspects.Among which sodium borohydride（SBH）and oxalic acid（OA）inhibited FeMn/biochar-H2O2 reaction,sodium thiosulfate（STS）slightly promoted degradation of pollutants in FeMn/biochar-H2O2 system.While hydroxylamine（HA）and oxalic acid（OA）can significantly enhance FeMn/biochar-H2O2 reaction and FeMn/biochar-H2O2-HA system showed best catalytic performance.FeMn/biochar-H₂O₂-HA system can degrade 92.8%of ciprofloxacin within 90 min when ciprofloxacin concentration,catalyst dosage,H₂O₂dosage and HA dosage was 10 mg/L,0.2 g/L,2 m M and 3 m M,respectively,which was higher than that（48%）in FeMn/biochar-H₂O₂-visible light system with the same dosage of FeMn/biochar and H₂O₂,indicating that FeMn/biochar-H₂O₂-HA system can effectively degrade contaminants with relatively lower catalyst and H₂O₂dosage.The prominent performance of FeMn/biochar-H2O2-HA system was attributed to the efficient surface metal cycle（Fe（III）/Fe（II）cycle and Mn（III）/Mn（II）cycle）and aqueous metal cycle(Fe³⁺/Fe²⁺cycle and Mn³⁺/Mn²⁺cycle)promoted by HA,which was beneficial for the generation of·OH.Besides,FeMn/biochar-H2O2-HA system can work effectively over various wastewater.Based on above-mentioned evidences,FeMn/biochar-H2O2-HA system is undoubtedly confirmed as a promising method that can be widely used to remove organic pollutants in water.