Preparation Of Graphite Phase Carbon Nitride Matrix Composites And Photocatalytic Antibiotic Degradation Performance

Semiconductor materials have great potential for photocatalytic degradation of organic pollutants.The degradation of organic pollutants in aqueous phase based on Fenton-like advanced oxidation process has attracted much attention.Under the assistance of light,the active substances produced by the catalyst itself and the free radicals produced by the activated oxidant enhance the degradation ability of organic pollutants under the synergistic effect.Graphitic carbon nitride（g-C₃N₄）has the advantages of good photocatalytic stability,green and simple synthesis process and easy functionalization.Therefore,g-C₃N₄was selected as the photocatalyst.However,the disadvantages of g-C₃N₄,such as high recombination rate of photogenerated electron-hole pairs（e^--h⁺）,narrow light response range and low surface charge transfer efficiency,limit its practical application.Therefore,in view of the shortcomings of g-C₃N₄,the photocatalytic performance is improved by designing and manufacturing nitrogen defects,metal doping and other semiconductor composites.In addition,the chemical structure and physicochemical properties of the catalyst were systematically studied,and the photocatalytic mechanism was discussed in depth.The research contents are as follows:（1）The integration of Fe-MOF-derived Fe₂O₃nanoparticles and nitrogen-deficient graphite phase carbon nitride by calcination,namely g-C₃N_x/Fe₂O₃.The g-C₃N_xand Fe₂O₃are constructed into a Z-type heterojunction,which enhances the light absorption ability of the composite catalyst and accelerates the migration and separation of photogenerated charges.In addition,N defects can act as electron trapping centers to suppress the recombination of photogenerated e^--h⁺pairs.After various characterizations,it was confirmed that g-C₃N_x/Fe₂O₃was successfully compounded.During the photocatalytic process,the active substances produced by g-C₃N_x/Fe₂O₃and the free radicals generated by activated H₂O₂synergistically promoted the degradation of oxytetracycline.In the g-C₃N_x/Fe₂O₃system,the degradation rate of oxytetracycline reached 87%.According to the quenching experiment,it was confirmed that·OH,·O₂^-and h⁺were involved in the chemical structure destruction of oxytetracycline in the photocatalytic reaction system.（2）The g-C₃N₄-ZnCu composite catalyst was synthesized by a simple one-step thermal polycondensation method.Zn and Cu were introduced into the framework of g-C₃N₄at the same time,and the structure and morphology of g-C₃N₄changed significantly,which confirmed the successful synthesis of g-C₃N₄-ZnCu catalyst.Compared with pure g-C₃N₄,the composite catalyst broadens the light absorption range and promotes the migration and separation of photogenerated charges.Under simulated sunlight irradiation,g-C₃N₄-ZnCu was excited by light to produce photogenerated e^--h⁺,which further produced active substances by redox reaction and activated potassium peroxomonosulfate（PMS）to produce free radical to synergistically degrade tetracycline hydrochloride（TC）.In the g-C₃N₄-ZnCu system,the removal rate of TC reached 91%under the optimal conditions,and the removal rate of TC was still above 80%after four consecutive cycles,indicating that the composite catalyst had good stability and reproducibility.According to the quenching experiment,it was proved that the main active substances such as SO₄^·-,·OH,·O₂^-and ¹O₂contributed to the TC removal process.（3）A simple physical mixing method was used to integrate FeCu-LDH with a thin layer of g-C₃N₄synthesized by thermal oxidation etching,namely g-C₃N₄/FeCu-LDH.FeCu-LDH and g-C₃N₄are constructed as Z-type heterojunctions,which enhance the light response ability and inhibit the photogenerated e^--h⁺pair recombination.In the photocatalytic process,the·OH and·O₂^-produced by the composite catalyst itself and the active free radicals such as SO₄^·-and·OH generated by the activation of PMS synergistically promote TC degradation.According to various characterizations,it was confirmed that the g-C₃N₄/FeCu-LDH catalyst was successfully prepared.In the g-C₃N₄/FeCu-LDH system,the removal rate of TC reached 99%under the optimal conditions.According to the quenching experiment,the main active substances such as SO₄^·-,·OH,·O₂^-and ¹O₂contributed to the TC removal process.