Construction Of Carbon-iron Dual-reaction-center Fenton-like Catalysts And Their Degradation Performance Of Antibiotics

Antibiotics are challenging to remove using traditional sewage treatment techniques because of their complicated structure and stability.The dual-reaction-center Fenton-like catalyst has become a research hotspot because it realizes the efficient decomposition of H₂O₂ and oxidation of pollutants through the electron-poor/electron-rich dual-reaction centers.Thus,developing of dual-reaction-center Fenton-like catalysts with high activity,high stability,and universality for various antibiotics have important valuable theoretical and engineering practical for the efficient treatment of different types of antibiotics.In this paper,starting from the design of dual-reaction centers structure and electron transport channel,three types of dual-reaction-center Fenton-like catalysts were constructed by hydrothermal and in situ pyrolysis/vulcanization methods with the guidance of density functional theory（DFT）.The typical antibiotics of tetracycline hydrochloride（TCH）,norfloxacin（NOR）,and amoxicillin（AMX）were taken as the representative to carry out the degradation experiment.The relationship between the structure,composition,and performance of the catalyst was systematically studied,the process conditions of antibiotic degradation were optimized,and the catalytic mechanism of catalysts and the possible degradation paths of three antibiotics were analyzed.The dual-reaction-center Fenton-like catalyst with universality for the efficient degradation of the above three antibiotics was selected for a preliminary 20 times scale-up experiment.The structure model of the dual-reaction center with C-O-Fe bond bridge as the electron transport channel was constructed by theoretical calculation,forming electron-rich Fe and electron-poor C centers.The Fenton-like catalyst containing C–O–Fe bond of Fe₃O₄ nanoparticles uniformly loaded on three-dimensional reduced graphene oxide（Fe₃O₄/rGO）was prepared by hydrothermal method.Under the condition of 9 mmol/L H₂O₂ and 0.8 g/L catalyst dosage,the degradation efficiency of TCH by Fe₃O₄/rGO-5 catalyst reached 98.7%within 60 min at p H=4.5.At p H≈6,the degradation efficiencies of TCH,NOR,and AMX were 96.9%,89.5%,and 93.2%within 90 min,respectively.In the Fenton-like process,·OH played a leading role.Antibiotics and their intermediates were adsorbed on the electron-poor rGO throughπ-πstacking,and the electrons were supplemented to Fe center through the C-O-Fe channel to complete the regeneration of≡Fe（II）,resulting in new·OH for the degradation of antibiotics.To shorten the electron transport distance,a dual-reaction-center structure model with short C-Fe bond bridge was constructed.The nitrogen-doped carbon nanotubes loaded with iron nanoparticles（Fe/Fe₃C/NCNTs）containing C-Fe bond Fenton-like catalyst was prepared by in-situ pyrolysis.The short C-Fe bond promoted the reduction of≡Fe（Ⅲ）to≡Fe（II）.The reaction rate constant of Fe/Fe₃C/NCNTs for norfloxacin degradation was 0.0109 min^-1.To solve the agglomeration of active center in the catalyst,Fe/Fe₃C/NCNTs on carbonized loofah（Fe/Fe₃C/NCNTs-CL）was developed with the loofah sponge as the carrier.When p H≈6,H₂O₂ concentration was9 mmol/L,and catalyst dosage was 0.6 g/L,the degradation efficiencies of TCH,NOR,and AMX by Fe/Fe₃C/NCNTs-CL-800 were 98.5%,93.8%,and 99.2%within 90 min,respectively.The agglomeration of active centers of iron nanoparticles was improved by the uniform dispersion of iron ions on the loofah,and the rate constant(0.0275min^-1)of norfloxacin degradation was 2.5 times of that the catalyst without loofa h sponge support.Based on the C-Fe dual-reaction centers,reducing S was introduced to construct a structural model containing C-Fe/C-S-Fe bond.Fenton-like catalyst of Fe₇S₈/SC with C–Fe dual-reaction center structure was prepared by hydrothermal and in-situ vulcanization methods.There were C-Fe and C-S-Fe interactions between Fe₇S₈ and carbon skeleton.The S^2-and S_n^2-in Fe₇S₈ had the reductive effect on≡Fe（Ⅲ）,which was advantageous in promoting the formation of≡Fe（II）.Moreover,the sulfur site can also obtain electrons from C-center through the C-S-Fe bond to achieve electron supplement,which greatly improved the Fenton-like catalytic activity of the catalyst.Reducing the catalyst amount to 0.2 g/L and shortening the reaction time to 40 min,three antibiotics of TCH,NOR,and AMX could degrade effectively by Fe₇S₈/SC-700,and the degradation efficiencies were as high as 99.3%,97.8%,and 98.9%.Fe₇S₈/SC-700 was selected for 20 times scale-up experiment,and the effects of inorganic anions and humic acid on Fenton-like degradation were studied.The degradation efficiencies of TCH,NOR,and AMX by Fe₇S₈/SC-700 were 95.7%,90.4%,and 98.4%within 60 min.In simulated AMX wastewater,Cl^-promoted the degradation of AMX,while NO₃^-,HCO₃^-,and humic acid all showed inhibitory effects on the AMX degradation.