Preparation And Theoretical Study Of Two-dimensional G-C₃N₄-based Nanomaterials

Graphite-like carbon nitride(g-C₃N₄)is a novel non-metallic semiconductor material with strong visible light response,high thermal and chemical stability,which has great potential for applications in hydrogen production by hydrolysis,degradation of organic matter,gas sensing and carbon dioxide reduction.In this thesis,two-dimensional g-C₃N₄ nanomaterials and their composites have been prepared and their photocatalytic degradation of organic compounds was investigated;the electronic properties as well as the optical and magnetic properties of the g-C₃N₄ adsorption system were studied based on the first principles.The main studies are as follows.In this thesis,two-dimensional g-C₃N₄ nanomaterials were prepared by a two-step method(thermal polymerization+liquid-phase ultrasonic exfoliation).SEM test results showed that the g-C₃N₄ nanosheet were exfoliated from graphite-like phase C₃N₄ materials with uniform and thin thickness;XRD showed that the g-C₃N₄ nanosheet were 3-s-triazine ring crystal structures.Finaly,the g-C₃N₄/MoS₂ composites were prepared by the impregnation-calcination method.SEM showed the morphology of uniform thickness nanosheets,and XPS and TEM indicated that the composites had both MoS₂ and g-C₃N₄ components and good crystal structures.Photocatalytic degradation of rhodamine B(RhB)experiments showed that after 90 min of light,the degradation efficiency of graphite-like phase C₃N₄,g-C₃N₄ nanosheet,MoS₂ and g-C₃N₄/MoS₂ composites were 80.2%,91%,91.5%and 99.4%,respectively,and the degradation rate of the g-C₃N₄/MoS₂ composites was 2.1 times higher than that of the monolayer g-C₃N₄ nanosheet.Thus,the successful composites of g-C₃N₄ with MoS₂ led to a significant improvement of the photocatalytic performance of g-C₃N₄ nanosheet.The electronic and ontical nrnerties of alkali monolaver g-C₃N₄ were theoretically investigated.The results show that the system is stable and the intrinsic g-C₃N₄ exhibits semiconductor properties while the alkali metal adsorbed g-C₃N₄ system shows metallic properties;the alkali metal adsorbed g-C₃N₄ shows a reduced work function;the alkali metal adsorbed system shows strong absorption peaks at visible light 380 nn,412 nm,420 nm and 476 nm,which facilitates the improvement of the photocatalytic activity of g-C₃N₄.In addition,the electronic,optical and magnetic properties of g-C₃N₄ adsorption by group ?A elements,CO and NO gases,respectively,and co-adsorption by group IIIA elements and gas molecules were investigated;the results show that all systems have negative values of adsorption energy,indicating good structural stability;the intrinsic g-C₃N₄ is a non-magnetic semiconductor,while the group ?A element adsorption g-C₃N₄ systems are all magnetic semiconductors;in the gas molecule adsorption g-C₃N₄ systems,the energy band structure of the CO/g-C₃N₄ system indicates that it is a non-magnetic semiconductor,while the NO/g-C₃N₄ system is a magnetic semiconductor,and charge transfer occurs between the gas molecules and g-C₃N₄,which facilitates the capture of the gas by g-C₃N₄;in the co-adsorption g-C₃N₄ systems of Group ?A elements and CO and NO gases,all systems show magnetic properties and have strong absorption peaks in the visible range.Thus,the results of this thesis provide potential candidate materials in terms of spintronic devices,gas sensors and photocatalysts.