Research On Synthesis And Properties Of High Catalytic Performance G-C₃N₄ Photocatalyst

Since entering the 21st century,the depletion of fossil energy and the deterioration of the environment have become the biggest problems affecting the development of human society and urgently need to be resolved.The new photocatalytic technology is able to use solar energy to decompose water to produce hydrogen and degrade environmental pollutants without secondary pollution,and has become one of the most promising technologies to solve the current energy crisis and environmental pollution.Titanium dioxide is one of the most widely studied photocatalysts in the field of photocatalysis as a representative of the first generation photocatalyst and has a high activity.However,its large bandgap leads to a narrow range of photoresponse,which makes solar energy utilization too low,which severely limits its application in reality.Therefore,a great deal of research has focused on the development of highly efficient semiconductor photocatalysts that can decompose water into hydrogen and degrade environmental pollutants under visible light irradiation.Some organic polymers and multiple metal oxide semiconductors exhibited a characteristic of visible light response.However,the lower specific surface area and higher photo-carrier recombination rate seriously affect their photocatalytic activity.Herein,the organic polymer semiconductor photocatalyst graphite phase carbon nitride?g-C₃N₄?was selected as the research object.According to its deficiency,the template-free method was designed to improve the specific surface area of the material.The specific content of this paper is as follows:1.Synthesize porous g-C₃N₄ to enhance its visible light catalytic performanceHigh-concentration HNO₃ solution was used to prepare small-size g-C₃N₄nanosheets under hydrothermal reaction conditions,and then the ultrafine water was removed by ammonia to remove impurities to obtain a carbon-defective small particle g-C₃N₄ nanometer with a specific surface area of 52 m²·g^-1.sheet.Through XRD,nitrogen adsorption-desorption,SEM,TEM,XPS,EPR and UV-vis,the formation process,composition,structure,specific surface area and pore size distribution,morphology and optical properties of the sample were analyzed.And discussed its formation mechanism.The treated sample increased the specific surface area of g-C₃N₄ from 5.4 m²·g^-1 to 52 m²·g^-1.The existence of large specific surface area and defects is beneficial to the adsorption of g-C₃N₄ to the reactants and the absorption of visible light.It is also conducive to the transport of photogenerated carriers and reactants on the surface of the material and the absorption spectrum of g-C₃N₄ obtained.A blue shift occurs,the energy band width increases by 0.11 eV,and a wider band width also favors suppression of electron-hole recombination.Finally,we analyzed the photocatalytic activity of the sample by using a visible light irradiation sample to vaporize the isopropanol gas.The results show that the photocatalytic activity of the porous g-C₃N₄ with large specific surface area and carbon defects is 9.6 times that of the original g-C₃N₄.This is mainly attributed to the fact that the porous structure enhances the specific surface area of the photocatalyst,increases the adsorption capacity of the photocatalyst to the reactants and the transportability of the reactants/products on the catalyst surface,and at the same time,the effect of defects causes the energy band structure of g-C₃N₄ to occur.Change,increase the redox ability of electrons and holes,thereby greatly improving the photocatalytic activity of the catalyst.2.Preparation of porous g-C₃N₄ nanosheets using supramolecular copolymers as precursors.Using melamine-citric acid supramolecular copolymer as a precursor,g-C₃N₄with porous nanosheet morphology was successfully obtained.The effects of melamine-citric acid ratio and heating method on the structure,morphology,specific surface area and photocatalytic performance of the formed g-C₃N₄ were systematically investigated.The formation process,structure,specific surface area and pore size distribution,morphology and optical properties of the samples were analyzed using various characterization methods,and the formation mechanism was discussed.The g-C₃N₄ obtained by the"secondary roasting"method with g-CN-3 has the largest porosity and the smallest number of layers,the specific surface area is 269m²·g^-1,and the energy band is larger than that of pure g-C₃N₄.At 0.06 eV,the lower number of layers and porosity increase the electron mobility of the sample.The photocatalytic test of the sample showed that the activity of the porous g-C₃N₄nanosheet was 5.5 times that of the original g-C₃N₄.