Acceleration Of Goethite-catalyzed Fenton-like Oxidation Of Ofloxacin By Biochar

Ofloxacin?OFX?is one kind of quinolone antibiotic that has been widely used in medical,breeding and animal husbandry industries.The entering of ofloxacin into environments during its production and application brings potential ecological risks.Iron-bearing mineral-catalyzed heterogeneous Fenton-like oxidation technology can be used for antibiotics degradation.However,the cycling of Fe?III?/Fe?II?in heterogeneous Fenton-like systems is slow.Improving Fe?III?/Fe?II?conversion efficiency is the key issue for promotion of the catalytic activity of heterogeneous Fenton-like systems.It has been suggested that the addition of reducing and complexing agents could improve the Fe?III?/Fe?II?conversion efficiency and catalytic activity in Fenton-like systems.Biochar?BC?is a carbon-enriched material derived from the pyrolysis of biomass under limited oxygen.BC is not only widely sourced and low cost,but also has good redox activity.It can adsorb and complex with metal ions.Here,this study explored whether BC could promote OFX degradation in goethite?Gt?catalyzed Fenton-like system.BC300 and BC600 samples were prepared by pyrolysis of wheat straw at 300? and600?,respectively.It was found that BC greatly stimulated the degradation of OFX in Gt-mediated Fenton-like system.In 4 h,while only 38.4%and 48.4%OFX?20 mg/L?were removed in Gt/H2O2 and BC600/H2O2 systems,the removal efficiency reached over 94.0%in Gt/BC600/H2O2 system.And the pseudo-first-order rate constant of Gt/H2O2,BC600/H2O2and Gt/BC600/H2O2 systems were 0.12,0.16 and 0.72 h^-1,respectively,indicating the occurrence of synergistically catalytic degradation.BC600 showed better stimulation effects than BC300.Through investigation of the impacts of factors like BC concentration?0-0.4g/L?,H2O2 concentration?0-4 mM?and pH condition?2-7?,the optimum reaction condition of Gt/BC600/H2O2 system was determined to be 0.2 g/L Gt,0.3 g/L BC600,2 mM H2O2 and pH 3,which led to 94.2%OFX degradation within 4 hours.Around 94.2%,87.8%,82.4%and75.5%OFX were removed in a four-round repeated treatments,which indicated the good stability of catalytic OFX degradation in the Gt/BC600/H2O2 system.The results of free radical scavenging experiment and electron spin resonance spectrum analysis showed that·OH was the main oxidant in the Gt/BC600/H₂O₂ system.Both the H₂O₂utilization efficiency and the·OH production in the Gt/BC600/H₂O₂ system were higher than those of Gt/H2O2 and BC600/H2O2 systems.BC600 was pre-treated with H2O2 to partially eliminate the persistent free radicals?PFRs?on its surface.The OFX removal efficiency in Fenton-like systems added with BC600 depleted-24 were around 11%lower than those of their counterpart systems added with pristine BC600 samples,indicating that the PFRs of BC participated in the oxidative degradation of OFX.The results of Fe species analysis,X-ray spectroscopy and FTIR analysis showed that although BC could not directly reduce the Fe?III?in Gt,it improved the cycling of Fe?III?/Fe?II?through complexing with Fe?III?by its carboxyl group.HPLC-MS analysis detected 8 OFX degradation products in the Gt/BC600/H2O2 system.It was speculated that the potential pathways of OFX degradation in the Gt-BC coexisting Fenton-like system included demethylation,defluorination,hydrogen loss and hydroxylation reactions.