Enhanced Norfloxacin Degradation By Iron And Nitrogen Co-doped Biochar Via Persulfate Activation

Between 2000 and 2015,the total global consumption of antibiotics rose from 21.1to 34.8 billion DDDs（defined daily doses）,and their long-term abuse posed a significant threat to the aquatic environment.Antibiotics in the liquid phase are not effectively removed after the traditional and advanced treatment units of the sewage treatment plant,and it may still accumulate in the biosolids,which triggers the risk of the spread of antibiotic resistance genes in the aquatic environment.Therefore,the development of an efficient antibiotic degradation process has become increasingly urgent.In recent years,sulfate radicals based advanced oxidation processes（SR-AOPs）have attracted in the field of antibiotic treatment,due to its extensive attention higher oxidation-reduction potential（E₀=2.5-3.1 eV）,longer half-life（30-40μs）,and resistance to pH changes,good adaptability and cost-effective.In this study,a one-step carbonization-pyrolysis method was applied to synthesize a new type of iron and nitrogen co-doped biochar catalyst（Fe@N co-doped biochar）,which was first applied to norfloxacin（NOR）removal through persulfate（PS）activation.In this study,we systematically studied the performance of the catalyst to adsorb and degrade NOR under different influencing factors,explored the catalytic mechanism of Fe@N co-doped biochar activated PS,and proposed the degradation pathways of NOR.The main content and discussion are as follows:（1）This paper uses a direct carbonization pyrolysis process to transform maize straw into a series of highly efficient heterogeneous catalysts.It was confirmed by SEM,FE-TEM,XRD,XPS,BET,Raman,FTIR and other characterization methods that the iron and nitrogen co-doping modification method successfully doped the iron element in the form ofα-Fe⁰,α-Fe₂O₃ crystals in the biochar,it also endows the biochar with a mesoporous structure with a high specific surface area,a higher degree of surface defects,abundant active sites,and vast nitrogen and oxygen-contained functional groups.（2）The electron paramagnetic resonance test（EPR）confirmed that·OH,·SO₄^-and¹O₂ are the three main active oxygen species in the catalytic reaction.Through combined XPS and quenching experiments,the catalytic mechanism was proposed,that is,α-Fe⁰,α-Fe₂O₃ activate PS through electron transfer to produce·OH and·SO₄^-,nitrogen-containing functional groups（Graphical-N,C-OH/C=N）accepted electrons from PS to generate ¹O₂.（3）A heterogeneous persulfate advanced oxidation system through Fe@N co-doped biochar was applied to construct a heterogeneous persulfate advanced oxidation system for antibiotic degradation.The effect of NOR degradation under different conditions were systematically investigated and the optimal reaction conditions were screened out.It was found that under the optimal reaction conditions,10 mg/L NOR could degrade 95%within 20 minutes.After five repetitive experiments,the removal rate of NOR can still reach 80%,and almost 50%of the NOR is completely mineralized,showing highly efficient catalytic degradation ability.（4）The possible degradation pathways of NOR were proposed by UPLC-TOF/MS,including defluorination,decarboxylation,piperazine ring breakage and nalidixic ring transformation.