Theoretical Study On The Photocatalytic Properties Of The C₄N/MoS₂ Composite Heterostructure And Novel 2D-COFs

In this thesis,density functional theory（DFT）based on first-principles is used to design and construct the microscopic structures of the C₄N/MoS₂van der Waals heterostructure consisted of two-dimensional covalent organic frameworks（2D-COFs）C₄N monolayer and molybdenum disulfide（MoS₂）monolayer and six novel2D-COFs theoretically.The visible photocatalytic properties of C₄N/MoS₂and six novel 2D-COFs are revealed in depth by theoretical calculations.The structure,electronic structure and optical properties of the C₄N/MoS₂heterostructure were studied by using the Perdew-Burke-Ernzerhof（PBE）of the generalized gradient approximation（GGA）and grimme dispersion correction for van der Waals interaction correction DFT-D2.The calculation for structural stability shows that C₄N monolayer and MoS₂monolayer can be combined to form thermodynamically stable heterojunction structures under van der Waals interaction.The electronic structure proves that the band gap of the C₄N/MoS₂heterostructure is smaller than that of MoS₂monolayer and C₄N monolayer under the interlayer interaction of van der Waals.The C₄N/MoS₂heterostructure is a type-Ⅱheterostructure.It was predicted to show potential photocatalytic activities on carbon dioxide reduction and oxygen evolution reaction.The electrostatic potential and charge density difference show that a built-in electric field exists at the interface,and the built-in electric field drives the effective separation of photogenerated charges.The absorption spectrum indicates that the C₄N/MoS₂heterostructure has strong visible light absorption ability comparing with C₄N monolayer and MoS₂monolayer.The photocatalytic capacity of the C₄N/MoS₂heterostructure is deeply revealed by analysis,which shows that the C₄N/MoS₂heterostructure would be an effective novel visible photocatalyst theoretically.Six rhombohedral pore novel 2D-COFs structures were designed by condensation reaction between 1,2,4,5-tetrasubstituted（amino,aldehyde,nitro）benzene or 3,5,9,1-tetrasubstituted（amino,aldehyde,nitro）biphenyls and 1,4-substituted（aldehyde,amino）benzene to form imine bond（-C=N-）and azo bond（-N=N-）linkages.The band structure,density of state,absorption spectrum and free energy of hydrogen evolution reaction of the 6 novel 2D-COFs were calculated by PBE functional.By comparing study,the COF-TBI-a composed of 1,2,4,5-tetraaminobenzene and 1,4-benzaldehyde through imine bond shows the strongest visible light spontaneous hydrogen evolution reaction ability.The mechanism of photocatalytic hydrogen evolution reaction driven by visible light is revealed by analyzing the free energy change of hydrogen evolution reaction,which provide theoretical basis for the design of novel photocatalysts.