Synthesis Of Graphite Carbon Nitride Photocatalytic Materials For Hydrogen Evolution Performance

In recent years,due to the development of industry and social progress,human life has gradually stepped into civilization.However,while improving material living standards,human activities have run counter to the sustainable development strategy proposed by modern society in order to relieve the pressure on energy resources.The active exploration of sustainable and environmentally friendly energy resources is imminent.As a kind of clean energy,compared with other energy sources,hydrogen has abundant storage value,environmental protection in the production process,and the utilization process is also in line with my country’s sustainable development strategy,so it is considered as one of the reasonable substitutes for fossil fuels.An increasing number of researchers are beginning to explore its huge application prospects in renewable energy production and solving environmental problems.Solar energy is an inexhaustible and inexhaustible green energy.However,our use of solar energy is still very limited,so it is of great significance to explore new directions to improve the utilization rate of solar energy.It is worth noting that the reaction of splitting water into hydrogen under visible light irradiation can make full use of abundant solar energy and successfully convert solar energy into chemical energy.Semiconductor photocatalyst is a common material for photocatalytic hydrogen evolution.Under the irradiation of visible light,electrons from the semiconductor valence band can transition to the conduction band,thereby obtaining more electrons to participate in the photocatalytic hydrogen evolution reduction reaction.Since the observation of the generation of H₂ and O₂ on the TiO₂ single crystal electrode under near ultraviolet light has made it possible to produce hydrogen and oxygen through the conversion between light energy and chemical energy.For the problem of low utilization of visible light photon energy,and the photocatalytic system has high requirements on the conduction band and valence band potential of semiconductors,it is difficult to meet them at the same time.Therefore,we should actively seek and develop some reactive material that can be applied to photocatalytic hydrogen evolution reduction.Graphite-like carbon nitride（g-C₃N₄）has attracted widespread attention since it was discovered.It presents a lamellar structure with triazine ring and slowly enters the public’s vision,because it is non-toxic,easy to prepare,strong chemical stability,and the band structure can meet the potential requirements of oxidation and reduction of water to produce hydrogen.However,g-C₃N₄ also has some inherent defects that limit its application:low absorption efficiency of visible light,small specific surface area,low separation rate of photogenerated electrons and hole pairs,etc.Aiming at the above shortcomings,this article starts from the perspective of modifying the morphology of g-C₃N₄,and prepares g-C₃N₄ with a unique morphology through supramolecular self-assembly one-step method;from the perspective of constructing a heterojunction,it is combined with other materials The ternary recombination has achieved improvements in the specific surface area of g-C₃N₄,the separation of photo-generated electrons and hole pairs,and the performance of photocatalytic hydrogen evolution.The specific work content is as follows:（1）A 3D peony-like sulfur-doped g-C₃N₄ by ternary self-assembly for efficient photocatalytic hydrogen productionA simple,template-free and low-cost ternary self-assembly method was developed to synthesize 3D peony-like sulfur-doped mesoporous g-C₃N₄ with high surface area and high photocatalytic performance.Thiocyanuric acid is introduced as the third component,which self-assembles with melamine and cyanuric acid through hydrogen bonds to form supramolecular intermediates.Compared with the traditional melamine-cyanuric acid binary self-assembly,the calcined appearance changes from a spherical shape to a peony shape.The layered stacking structure of the peony-like SCNx sample can effectively increase its specific surface area and the number of active sites and the release rate of photocatalytic hydrogen is52.6 times higher than that of BCN.Compared with other metal photocatalysts,the preparation process of peony-like sulfur-doped g-C₃N₄ ingeniously introduces sulfur into the precursor while supramolecular self-assembly,which greatly shortens the reaction time and avoids the traditional method.Other impurities are introduced during the sulfur doping process.At the same time,the relationship between its morphology and photocatalytic activity was proved by TA spectroscopy and electrochemical analysis.Combined with the characterization results of XRD,XPS,BET,UV-Vis,etc.,a possible photocatalytic hydrogen evolution mechanism is proposed.（2）Construction of 1D/0D/2D g-C₃N₄ ternary heterojunction composite material for efficient photocatalytic hydrogen evolutionIn this study,we easily prepared a three-component all-solid 1D/0D/2D g-C₃N₄（CN）ternary heterojunction composite material through conventional hydrothermal and chemical precipitation methods.The particles are deposited on the surface of the 2D g-C₃N₄,and then combined with 1D Zn_0.5Cd_0.5S（ZCS）nanotubes to form a stable ZCS/PdAg/CN composite structure.The PdAg bimetallic nanoparticles make a close contact interface between CN and ZCS.Under visible light irradiation,both CN and ZCS are excited,and PdAg can act as an electron transport medium to accelerate the extraction and utilization of photo-induced electrons from ZCS to the CN surface.In addition,the CN layer reduces the photocorrosion of the ZCS,enhances the specific surface area of the composite material,and greatly improves the performance of photocatalytic hydrogen evolution.After performance testing,the composite material with 30 wt%ZCS and 4 wt%PdAg exhibits the best hydrogen evolution performance,which is 753 times the hydrogen evolution rate of single-component CN,and 12.6 times the hydrogen evolution rate of the component ZCS/CN.Combining the characterization results of PL,XRD,XPS,BET,UV-Vis,etc.,a possible photocatalytic hydrogen evolution mechanism is proposed.