Synthesis Of Metal Oxide/g-C₃N₄ Composite Material And Its Photocatalytic Hydrogen Production Performance

The progress of science and technology is accompanied with consumption of energy.Whether it is the era of steam instead of manual factories or the era of electricity instead of steam,it is accompanied by the consumption of traditional energy sources such as coal and oil.The storage of coal and petroleum energy is limited and unevenly distributed.In the near future,traditional energy will become a scarce resource.Therefore,it is urgent for us to develop a new energy source that is easy to obtain and widely distributed.Solar energy is inexhaustible.How to effectively use the energy of solar energy to convert it into other new energy sources is important.In addition,solar energy is widely distributed,stable,high energy density,clean and environmentally friendly,easy to store and transport,so how to use solar energy to convert and obtain hydrogen energy is a promising way.Photocatalytic cracking of water to produce hydrogen is a research project with good development prospects.The use of sunlight to decompose water under the action of photocatalysts to obtain hydrogen energy has attracted widespread attention,and catalysts with high catalytic activity and stability have become key factors.Among many catalysts,graphite phase carbon nitride（g-C₃N₄）is an organic polymer semiconductor that can absorb visible light.It is easy to prepare.Graphite carbon nitride with good morphology can be prepared only by heat treatment with melamine.However,its weak absorption of visible light,fast photogenerated electron-hole recombination,and small specific surface area limit its photocatalytic hydrogen production activity.Therefore,to effectively improve its photocatalytic activity is important.As a widely used modification method,loading can expand the absorption of visible light by introducing new substances on g-C₃N₄,inhibit the recombination of photogenerated electron-hole pairs,increase the surface area,and improve the catalytic hydrogen production activity.The graphite phase carbon nitride is compounded with La₂O₃ by a one-step method.The AFM characterization shows that the prepared composite material has a few-layer lamellar structure,and the thickness of the g-C₃N₄ lamellar is about 2.3 nm,which is only three to five layers of g-C₃N₄ thickness,and the thickness of the La₂O₃ sheets is 2.9 nm.The BET test results show that the specific surface area of the composite material is increased to about 10 times than g-C₃N₄,and the increased specific surface area helps to expose more active sites.The fluorescence test shows that the photogenerated electrons of the composite material have a longer lifetime.The composite material loaded with La₂O₃ has a shorter electron transmission path,and La₂O₃ has a good electron transmission efficiency.These factors all contribute to the more photogenerated electrons transfer to the surface to participate in the redox reaction and increase the photocatalytic hydrogen production activity of g-C₃N₄.In the stability test of the composite material,after four cycles of La₂O₃,the total amount of photocatalytic hydrogen production was still 83.9%than total amount of the first cycle,indicating that the photocatalytic performance of this composite material was relatively stable.Using indium nitrate as the source of indium,the In-MOF precursor is prepared in an autoclave,and then the prepared precursor is mixed with melamine,and the mixture is heat-treated in a tube furnace with nitrogen as a protective gas to obtain In₂O₃ supported g-C₃N₄ composite material.FESEM can see that the surface of this composite material has a porous lamellar structure.The nitrogen adsorption and desorption results show that the specific surface area and pore diameter of the composite material loaded with In₂O₃are about 1.5 times than g-C₃N₄,and the pore volume of the composite material is about2.3 times than g-C₃N₄.The band gap spectrum and conduction band of g-C₃N₄ and In₂O₃can be obtained through the Kubelka-Munk function and the Mott-Schottly basis point.The valence band and the conduction band can be obtained from the conduction E_VB=E_CB+E_g.The heterojunction is successfully constructed from g-C₃N₄ to In₂O₃.In addition,through DFT calculations,it can be seen that the construction of heterojunction caused the accumulation of holes and electrons from g-C₃N₄ to In₂O₃ to produce a polarization field,which can effectively promote the separation of photogenerated electron-hole pairs,and the increase of the specific surface area is conducive to the exposure of more surface active sites,and the synergistic effect of the constructed heterojunction and increased specific surface area promote the enhancement of catalytic activity.