Performance And Mechanism Study On Degradation Of Nitrochlorobenzene In Soil By Peroxymonosulfate Activated With Cobalt Ferrite Supported On Biochar

Chlorine-containing organic pollutants are widespread and toxic,and their degradation in natural environment is slow,making remediation in contaminated soil challenging.Among chlorine-containing organic pollutants,nitrochlorobenzenes,which are widely used in the production of pesticides,dyes and pharmaceuticals,have received widespread attention because of their strong carcinogenicity,mutagenicity and difficult degradability.For organic pollutant treatment technology,compared with traditional technologies such as physical adsorption,biodegradation and chemical degradation,advanced oxidation technology based on persulfate has advantages of faster reaction rate and stronger oxidation capacity.However,its practical application is still restricted by persulfate activation efficiency and the uncertainty of actual polluted site.Therefore,the development of efficient and stable catalyst and the systematic investigation of the influence of complex environmental factors will be conducive to the construction of an advanced oxidation system,which could be effectively and scientifically applied to actual organic contaminated sites.In this paper,firstly,biochar obtained from natural rice husk was used as a carrier and solgel method was applied to prepared biochar-loaded CoFe₂O₄ catalysts（CoFe₂O₄@BC）,which had higher stability and catalytic activity than the conventional CoFe₂O₄.After screening of types,ratios and calcination temperatures of precursor,the influences of main parameters such as the PMS dosage,catalyst dosage and p H on the degradation of p-NCB in the aqueous and soil phases by CoFe₂O₄@BC/PMS were investigated,and the stability of the catalyst was evaluated by cyclic experiments.Next,in order to clarify p-NCB degradation process in CoFe₂O₄@BC/PMS system,the catalyst crystal structure,surface morphology,surface functional groups and elemental valence states were analyzed by XRD,SEM,FTIR and XPS technologies.On this basis,the roles of BC in improving the dispersion of CoFe₂O₄,enriching the target contaminants and promoting the electron transfer of the composite was also described.The reactive oxygen species in system were identified by quenching experiments as well as EPR and the dominate reactive oxygen species in system were ·OH、surface SO4·-、O2·-.In addition to the determination of degradation intermediates and analysis of system toxicity using mass spectrometry techniques and biotoxicity simulations/experiments,the dechlorination and mineralization rates in p-NCB degradation process were also analyzed to illustrate the environmental friendliness of the CoFe₂O₄@BC/PMS system for the treatment of p-NCB.Further,the environmental matrix in the actual contaminated sites can affect the advanced oxidation process,as a result,the performance of the CoFe₂O₄@BC/PMS system was investigated when environmental matrix（Cl-、HCO3-、HPO42-and humic acid）were introduced.By varying the types and relative concentrations of the environmental matrix,their effects on p-NCB degradation were evaluated.The radical quenching,PMS activation,system p H adjustment and catalyst active site occupation roles of each environmental matrix in the system were described separately.Finally,in order to evaluate the performance of the CoFe₂O₄@BC/PMS system when dealing with contaminants in continuous migration state,one-dimensional column degradation experiment was carried out.99.5% quartz sand and 0.5% catalyst were used as the column filling medium,and the p-NCB concentration at the bottom inlet of the column was set at 10mg/L.The effects of feed flow,PMS concentration and background metal ions on the degradation system were investigated.It was determined that in the one-dimensional column degradation system,the increase of feed flow would lead to the increase of pollutant concentration at the exit of the column,but the amount of pollutants removed per catalyst was larger.It was clarified that the increase of PMS concentration in the feed solution and the introduction of background ions had a positive effect on the removal of target pollutants.In this paper,the performance and mechanism of CoFe₂O₄@BC/PMS system were analyzed,and the environmental matrix influencing factors,environmental toxicity analysis and one-dimensional column dynamic degradation system were introduced to provide a comprehensive description of CoFe₂O₄@BC/PMS system,which will provide more theoretical basis in practice.