Preparation And Photocatalytic Hygrogen Evolution Performance Of Porous 3D G-C₃N₄ Based Composite Photocatalyst

Graphite phase carbon nitride(g-C3N4)has attracted widespread attention in the field of photocatalytic water splitting due to its many advantages,such as simple preparation method,cheap raw materials,good physical and chemical stability,together with adjustable band gap.The g-C3N4 obtained by the traditional direct thermal polymerization method exhibits a stacked block structure,resulting in small specific surface area,limited light absorption capacity,and poor photocatalytic performance consequene.In order to overcome these shortcomings,this thesis aims at designing a cheap,high-performance g-C3N4 based photocatalyst by i)controlling morphology to improve specific surface area and the active sites involved in the reaction,and ii)compounding with other co-catalysts to improve the visible-light-driven photocatalytic HER efficiency.The specific research contents are shown as follows:A supramolecular self-assembly method was used to prepare 3D g-C3N4(DCN)with a three-dimensional(3D)interconnected framework morphology by using melamine and cyanuric acid as raw materials and water as solvent.The specific surface area of 3D g-C3N4 reaches 112.3 m2 g-1.Subsequently,a simple hydrothermal method was used to prepare the non-noble metal promoter 1T-WS2,which was coupled with DCN to prepare a porous 3D g-C3N4/1T-WS2 composite photocatalyst through a self-assembly process.The photocatalytic hydrogen production test shows that the photocatalytic HER rate of 3D g-C3N4/1T-WS2(DCN-25%)is about 218μmol g-1h-1 after optimizing the loading under the visible light of λ≥420nm,which is approximately 18 times that of DCN without co-catalyst.No significant decrease of hydrogen production amount after five cycling runs was observed,showing the good stabiltity of DCN-25%photocatalyst.The photoelectrochemical assay results and fluorescence spectroscopy show that 1T-WS2 can significantly enhance the charge transport of the composite photocatalyst and inhibit the recombination of electron-hole pairs,which proves that 1T-WS2 is a potential photocatalytic hydrogen production co-catalyst.In order to avoid destroying the morphology of DCN or incorporating other alien heteroatoms into the DCN molecular structure during the process of supporting the co-catalyst,it is very important to choose a suitable method of introducing the co-catalyst.Herein,NixP was precisely loaded on the electron outlet points of.DCN by in-situ light deposition and finally a porous 3D g-C3N4/NixP composite photocatalyst was prepared.Photocatalytic performance test results show that the photocatalytic HER rate of DCN-20 under the optimal light deposition time of 20 min reached 1720 μmol g-1h-1,which is far higher than that of pure DCN(12μmol g-1h-1)and BCN/NixP(BCN-20)(15μmol g-1h-1).No significant decrease of hydrogen production amount after five cycling runs was observed,indicating the good stabiltity of DCN-20 photocatalyst.UV-vis absorption spectra shows that the DCN-20 photocatalyst has stronger absorption in visible light region.The reason for the photocatalytic performance improvement of was experimentally analyzed by photoelectrochemical test and PL characterization.These results indicate that the DCN-20 possess an efficient carrier separation and transport efficiency,together with a smaller interfacial charge transfer resistance.This work provides a new research ideas for the preparation of non-precious metal g-C3N4-based photocatalysts.