First-Principles Study Of Efficient Two-Dimensional Carbon Nitride-Based Van Der Waals Heterojunction Photocatalysts

Photocatalytic technology converts solar energy into hydrogen energy by photosplitting water,realizing the chemical conversion and storage of clean energy,which is expected to completely solve the increasingly serious energy and environmental problems.In this thesis,aiming at the narrow photoresponse range and low photogenerated electron-hole separation efficiency that restrict the semiconductor photocatalysis technology,based on the first-principles density functional theory,so as to promote carbon nitride-based photogenerated electron hole pairs for the directional transfer and improve the quantum efficiency of photocatalytic reaction as the main line,starting from the construction of carbon nitride-based van der Waals heterojunctions.On the one hand,the microscopic mechanism of interfacial interaction and interfacial photogenerated carrier migration is discussed,and the effect of effective heterojunction interface and photogenerated electron and hole separation on the photocatalytic activity of the material is revealed.On the other hand,the effect of adjusting the interlayer spacing and applying an electric field on photocatalytic materials are explored,and feasible schemes for effectively regulating the photocatalytic performance are identified.As a result,the construction of carbon nitride-based catalysts with stable structure,excellent performance and high efficiency are realized,and the mechanism for effectively regulating of photocatalytic performance is established,which broaden the horizon for experimenters to design high-efficiency carbon nitride-based van der Waals heterojunctions photocatalysts.The main research contents are as follows:（1）Photocatalytic properties of Silicon Carbide/Carbon Nitride（Si C/C₂N）heterojunctions.The phonon dispersion and ab initio molecular dynamics analysis show that the Si C/C₂N Structure has good dynamical and thermodynamic stability.The band structure and atomic projected density of states of the Si C/C₂N heterojunction indicate a class type II heterojunction with a mild band gap of 1.58 e V,and its band edge position meets the redox potential requirements for water splitting,which greatly facilitates the effective separation of photogenerated electron-hole pairs and improves the catalytic activity.Moreover,the Si C/C₂N heterojunction also well retains the excellent visible light responsiveness of the original C₂N monolayer,further demonstrating its application potential as an efficient visible light-driven photocatalyst.（2）The photocatalytic properties of GaN/CNs heterojunctions formed by the composite of two different graphite-like carbon nitride materials（C₂N and g-C₃N₄）and gallium nitride materials were studied,and the performance comparisons were carried out.Due to its type II band alignment and high carrier mobility,the Ga N/C₂N heterojunction exhibits obvious advantages in promoting the efficient separation of photogenerated electron-hole pairs,while the better visible light absorption range and capability,making it promising in the application field of visible light catalyst.The Ga N/g-C₃N₄ heterojunction has a direct band gap of 3.43 e V,which is suitable for the field of optoelectronic devices.（3）The photocatalytic performance enhancement mechanism of carbon nitride-based heterojunctions was investigated.Based on the study content（1）,the band edge position of the Si C/C₂N heterojunction relative to the standard hydrogen electrode is regulated by the strategy of adjusting the interlayer spacing.Based on the study content（2）,the band gap and redox potential of the Ga N/C₂N heterojunction are regulated by applying an electric field.The results show that both adjusted interlayer spacing and applied electric fields can effectively regulate the band edge positions of standard hydrogen electrodes and enhanced visible light responsiveness.With the above methods,the purpose of regulating the visible light catalytic activity of carbon nitride-based photocatalysts by multiple means is achieved,and the hydrogen production efficiency of photocatalytic water splitting is further explored.