In-Situ Construction Of G-C₃N₄ Based Heterojunctions And Photocatalytic Performance

Converting solar energy into green chemistry energy is considered as a very promising way to alleviate the energy crisis and environmental problems.The key to this technology is to improve the activity of photocatalysts.Among numerous photocatalysts,g-C₃N₄has attracted widespread attention due to its visible light responsive band structure,non-toxic,inexpensive,and easy functionalization.However,the low utilization rate of visible light and high recombination rate of photocarriers result in unsatisfactory photocatalytic performance.This paper enhances the visible light absorption,promotes the separation and transfer of photocarriers,and improves photocatalytic performance by in-situ constructing g-C₃N₄based heterojunctions（Mott-Schottky heterojunctions and electron donor acceptor heterojunctions）.The main research content is as follows:（1）A low-temperature pyrolysis strategy of organic-inorganic hybrid was developed.Ultra-smallα-MoC nanodots with a diameter of 1.8 nm were successfully prepared,andα-MoC/g-C₃N₄Mott-Schottky heterojunction with interfacial electron transfer channel（Mo-N）was constructed in situ for the first time,which delivers a110-fold enhancement of H₂production compared to bare g-C₃N₄.The experimental results and density functional theory calculations revealed that the introduction ofα-MoC reduces the activation energy of hydrogen evolution reaction,and the interface chemical bond reduces the Schottky barrier,inhibits the recombination of photogenerated electrons,and improves the photocatalytic hydrogen production performance.（2）On the basis of the above,an in-situ topology strategy has been developed to achieve preparation of defect MoN fromα-MoC.Moreover,a MoN/g-C₃N₄2D/2D Mott-Schottky heterojunction with an interface electron transfer channel（Mo-C）was constructed in-situ,with a photocatalytic hydrogen evolution performance 120 times that of unmodified g-C₃N₄.Experiments have shown that the defect MoN ratioα-MoC presents more active site for hydrogen evolution.The Mott-Schottky effect promotes the separation and transfer of photogenerated carriers and improves the photocatalytic hydrogen production performance.（3）By copolymerizing two triazole based electron deficient monomers in the NaI system,the triazole ring was successfully inserted into the structure of poly（heptazine imide）,and the electron donor-receptor heterojunction DA-PHI was constructed.Its photo synthesis performance of H₂O₂reached 206μmol h^-1,41 times higher than unmodified g-C₃N₄.The apparent quantum yield is 29.0%at 400 nm.The research results indicate that Na doping and N vacancies enhance visible light absorption ability,electron donor-acceptor heterojunction enhances internal electric field,promotes the transfer of photoexcited electron from PHI unit to triazole unit,enhances the activation and reduction of oxygen,and improves the performance of photo synthesis of H₂O₂.