Preparation Of Chitin Carbon-based Composite Catalyst And Its Application In Fenton-like Catalytic System

Advanced oxidation technologies such as hydrogen persulfate（PMS）and hydrogen peroxide（H₂O₂）activation are widely studied and applied to wastewater treatment.In recent years,with the rise and application of various new carbon materials,carbon-based composite materials such as activated carbon,carbon nanotubes,graphene,carbon nitride,and biomass carbon have been studied a lot in advanced oxidation technology,and the reaction of the catalytic degradation of pollutants shows very excellent catalytic performance,and its potential application value is extremely high.Chitin is a common biomass raw material.It is widely present in the extracellular matrix of various invertebrates and is second only to plant cellulose in nature.In this paper,chitosan and its derivative chitosan are used as precursors.Heterogeneous biomass carbon-based composite catalysts are prepared by pyrolysis,sol-gel and mechanochemical methods for PMS,H₂O₂ and hydrogen sulfite.Advanced oxidation techniques such as sodium（Na HSO₃）activation,and explore its reaction mechanism.The specific work carried out is summarized as follows:（1）Manganese oxide octahedral molecular sieve（MnO₂）is a molecular sieve material with a tunnel structure.It shows good performance in advanced oxidation technologies such as PMS activation,but its activity is greatly affected by the p H of the solution.Based on the pyrolysis method to obtain chitin carbon material,a simple mechanochemical method was used to synthesize a composite catalyst（MnO₂/NC）of chitin carbon and MnO₂,and its structure was characterized.Compared with MnO₂ alone,the crystal form and morphology of MnO₂ in the MnO₂/NC composite catalyst have not changed significantly;however,there is a strong interaction between MnO₂ and carbon,resulting in valence of Mn species and the key of Mn-O bonds energy can be reduced.This interaction can significantly increase its activity of activating PMS to degrade pollutants such as acid orange 7（AO7）,and can adapt to different solution p H and repeated use.The study of the reaction mechanism shows that the conventional strong oxidative sulfate radicals and hydroxyl radicals have less degradation on the substrate,and the direct electron transfer process from pollutants to MnO₂/NC catalysts to PMS contributes more.（2）Homogeneous cobalt ion-bicarbonate system can effectively activate H₂O₂ to degrade many organic pollutants in wastewater,but there are few studies on the preparation of efficient heterogeneous cobalt-based catalysts to solve the problem of cobalt ion recovery.In this paper,a simple sol-gel method and a pyrolysis method were used to successfully synthesize the linear natural polysaccharide product chitosan obtained from the chitosan with all or part of its acetyl group as the carbon precursor and cobalt acetate as the metal cobalt source to synthesize the heterogeneous Co_xO_y/NC composite catalyst.The catalyst can activate H₂O₂ in an aqueous solution of HCO₃^-,thereby generating strongly oxidative·OH radical and degrading organic pollutant AO7.After various characterization analyses,it is confirmed that the main active species in the material is metallic cobalt,and the outer layer CN wraps the inner structure of the cobalt oxide compound,making it trapped in the catalyst,insoluble in water,and avoiding secondary pollution of cobalt ions.（3）Sulfite activation can also generate strong oxidizing SO₄^-·radicals.Compared with persulfate,sulfite has the advantages of low price and wide range,but the current researches are mainly based on homogeneous iron-based catalysts.In this paper,a simple sol-gel method and a pyrolysis method are used to prepare a heterogeneous Fe₃O₄/CN catalyst using chitosan as a biomass carbon precursor and ferrous sulfate as a metal iron source to activate hydrogen sulfite to degrading organic pollutant methyl orange（MO）.The experiment found that the pyrolysis temperature has a certain effect on the existing crystal form of the catalyst,and the various parameters of the reaction also have a certain effect on the catalytic activation performance of Fe₃O₄/CN,which leads to different manifestations of the degradation rate of MO as a macro.The experimental free radical quencher and EPR experiments show that although there are certain SO₄^-·and·OH radical in this system,the main active species are¹O₂ and O₂^-·.Although the catalyst’s reusable performance is still Need to be further improved,but Fe₃O₄/CN materials still have a certain relative stability.