Study On The Modification Of G-C₃N₄ And Its Photocatalytic Properties For Hydrogen Production

With the prompt development of global economy and society,the demand for traditional fossil fuels increases rapidly,which leads to the depletion of conventional hydrocarbon fuels as the human is about to face a severe energy crisis.Under the premise of the serious energy crisis,the problem of environmental pollution is becoming prominent increasingly,especially the problem of air pollution and water pollution.At present,most countries are faced with the energy crises and environmental problems demanding to be solved urgently.Without effective improvement strategies,human beings will not be able to achieve sustainable development.So if a new strategy can be used to develop a new type of catalyst that can absorb and utilize sunlight and converted it into chemical energy quickly to produce hydrogen from water splitting.The conversion of solar energy to clean and pollution-free hydrogen energy can not only solves the problem of environmental pollution,but also alleviates the energy crisis to a certain extent.Therefore,the preparation of CFB/NH₂-MIL-125（Ti）and g-C₃N₄/B-CTF-1 composite photocatalysts by chemical modification and covalent bonding were systematically discussed in this paper,as well as the research and application of the catalysts in the photocatalytic decomposition of water for hydrogen production.（1）In this paper,the lamellar g-C₃N₄ was synthesized by high temperature calcination and thermal oxidation stripping with thiourea as the precursor.On the basis of this,the g-C₃N₄ nanosheet was benzoized by chemical modification（CFB）.Then the g-C₃N₄ after benzoic acid was introduced into the precursor of NH₂-MIL-125（Ti）to form CFB/NH₂-MIL-125（Ti）.A new type of z-type heterojunction photocatalyst was formed by hydrothermal reaction,and the two photocatalysts were bridged by benzoic acid,which was also used as the electronic medium.The experimental results show that the g-C₃N₄ can increase the catalytic efficiency of photocatalytic activity for H₂ evolution.When the amount of coupling is10 wt%,the photocatalytic effect of the composite catalyst is the best for the decomposition of water to produce hydrogen.The rate of hydrogen production is as high as 1.123 mmol·h^-1·g^-1as much as 6 times that of pure NH₂-MIL-125（Ti）.At the same time,the composite catalyst has a high stability because of the benzoic acid which as a bridge.（2）In order to prepare a new type of metal-free semiconductor catalyst with high catalytic activity and high stability,a new synthesis strategy was proposed in this paper.First the terephthalonitrile as precursor,through reflux and high temperature calcination,to synthesis covalent organic frameworks（CTF-1）which is two-dimensional frame with the lamellar structure,then modified CTF-1 with diazo salt of p-aminobenzoic acid to form benzoic acid CTF-1（B-CTF-1）.After that,the lamellar g-C₃N₄ nanosheet was modified by amide-condensation reaction between the amino group at the edge of g-C₃N₄ and the carboxyl group on the surface of B-CTF-1under the action of condensation agent,to connecte two types of semiconductor.The experimental results show that when the coupling amount of B-CTF-1 is 10%,the photocatalytic decomposition of water for hydrogen production is the best,and the rate of hydrogen production reach up to 0.8454 mmol·h^-1·g^-1as much as 2 times and 5times than that of pure g-C₃N₄ and CTF-1,respectively.