Study On Modification Of Graphitic Carbon Nitride Nanosheets And Its Photocatalytic Performance

With the advantages of being green and making full use of solar energy,the degradation and conversion of pollutants by semiconductor photocatalysis is considered a promising way to alleviate environmental pollution and the energy crisis.Graphitic phase carbon nitride（g-C₃N₄）semiconductor materials have a unique electronic structure and excellent chemical stability,which make them promising photocatalysts and catalyst carriers.However,the single g-C₃N₄ has the disadvantage of low light utilisation and a vulnerability to compounding of photogenerated carriers.In order to solve such problems,this topic is based on the modification of g-C₃N₄ nanosheets,the composite materials were prepared by loading co-catalysts and constructing heterojunctions,which are applied to the degradation of antibiotics and the depolymerization of lignin respectively according to the different properties of the materials.Finally,characterization analysis and radical trapping experiments were carried out,on the basis of which the reaction path and mechanism of catalysis were elaborated,providing a theoretical basis for the modification and application of g-C₃N₄ photocatalysts.The specific research contents and results of this topic are as follows:（1）Theα-Fe₂O₃/g-C₃N₄ composite photocatalyst was prepared and applied to degrade antibiotics in water.Theα-Fe₂O₃ clusters were successfully introduced on the surface of g-C₃N₄nanosheets by self-assembly method and calcination.Since trinuclear iron clusters（Fe₃）can be converted toα-Fe₂O₃ clusters after calcination,the ratio ofα-Fe₂O₃ clusters to g-C₃N₄nanosheets was regulated by changing the loading of Fe₃ on g-C₃N₄ nanosheets.The results of photocatalytic experiments using tetracycline hydrochloride as the target antibiotic contaminant showed that the composite（CFCN-8）degraded tetracycline hydrochloride best when the Fe₃solution was added at 6 m L.To further improve the degradation efficiency,the photocatalytic reaction was assisted with a Fenton reaction and CFCN-8 achieved 87%degradation of tetracycline hydrochloride within 45 min.The enhanced catalytic performance can be explained by the fact that the photo-Fenton method induces a cyclic conversion of Fe²⁺and Fe³⁺,which not only improves the cyclic stability of the reaction but also promotes the separation of electron-hole pairs.（2）The Zn₄In₂S₇/g-C₃N₄ heterojunction photocatalyst was prepared and applied to the conversion of lignin model substances as a means of studying the mechanism of lignin depolymerisation.Zn₄In₂S₇/g-C₃N₄ composites were prepared by the in situ water bath method and the composite ratio of Zn₄In₂S₇ to g-C₃N₄ was adjusted by varying the amount of g-C₃N₄nanosheets added.Using 2-phenoxy-1-phenylethanol（PP-ol）as a lignin model substance,Zn₄In₂S₇/g-C₃N₄ selectively breaks theβ-O-4 bond in PP-ol.The optimum ratio composite of Zn₄In₂S₇ to g-C₃N₄（ZCN-200）converted up to 99%of PP-ol in 3h at room temperature,with the selective conversion products being phenol and acetophenone.The UV-visible absorption spectra（UV-vis）and optoelectronic properties of the materials show that the band gap of the Zn₄In₂S₇/g-C₃N₄ composite is narrowed compared to g-C₃N₄,from improving the light absorption capacity of g-C₃N₄;meanwhile,the g-C₃N₄ and Zn₄In₂S₇ energy bands are matched,forming a type II heterojunction with good ability to separate electrons and holes.