Preparation Of Cu_2-xSe-based Photocatalytic Materials And Study On Their Performance Of Photocatalytic Hydrogen Production

In recent years,Green sustainable development has aroused rising attention for the progressively severe environmental pollution and energy problem.Hydrogen energy,a clean renewable energy source,is critical to address the above issues.The use of solar energy for photocatalytic splitting of water to produce hydrogen is a new green technology to prepare hydrogen.However,the traditional semiconductor photocatalysts（such as Ti O₂,Zn O,and Cd S）only respond to ultraviolet light（about 4%of solar energy）or have poor chemical stability due to their large band gap,which seriously hinders the development of photocatalytic technology.At present,exploring high-efficiency visible light semiconductor photocatalysts has become a research hotspot in the field of photocatalysis.Copper selenide(Cu_2-xSe)is p-type semiconductor with a cubic crystal system and a band gap of 1.4 e V-2.2 e V.Because of its excellent visible light capture capability and rapid photoelectric response performance,it has a broad vision of application in the field of photocatalysis.This paper takes Cu_2-xSe as the main research object for the first time,screens out the best preparation conditions of monomer Cu_2-xSe and constructs Cu_2-xSe/rGO and Cu_2-xSe/g-C₃N₄heterojunction systems,respectively.The microstructure,photoelectric performance and photocatalytic performance of the system were characterized,and the photocatalytic reaction mechanism was deeply analyzed.The specific research contents and conclusions are as follows:（1）In this paper,a simple hot-injection method is used to prepare monomer Cu_2-xSe,and the factors such as surfactant and reaction temperature in the reaction process are controlled to prepare a highly efficient and stable Cu_2-xSe photocatalyst.The best process conditions were selected:Cu（NO₃）₂and Se were used as the copper source and selenium source,ascorbic acid（AA）was used as the modifier,the reflux reaction temperature was230℃,and Cu_2-xSe nanoparticles with uniform distribution and optimal hydrogen production performance was prepared by this reaction conditions.（2）Cu_2-xSe/rGO photocatalyst was prepared by in situ hot-injection method,and rGO as a good electron acceptor was combined with Cu_2-xSe to construct heterojunction.By controlling the amount of rGO added,Cu_2-xSe/rGO heterojunction complexes with different rGO contents were prepared,and their photocatalytic performance was evaluated through the photocatalytic hydrogen production experiment,and the photocatalytic reaction mechanism was proposed.The experimental results show that Cu_2-xSe/3%rGO has the highest photocatalytic hydrogen production rate.The average rate in 3 h can reach3123.48μmol·g^-1·h^-1,which is about 3.46 times than the hydrogen production rate of the monomer Cu_2-xSe.This is attributed to the introduction of rGO,which promotes the separation and migration of photo-generated carriers and is beneficial to the photocatalytic reactions process.Four cycles of experiments show that the photocatalytic hydrogen production rate of Cu_2-xSe/3%rGO remains unchanged and has good chemical stability.（3）In this experiment,melamine was used as the precursor,g-C₃N₄was prepared by thermal polycondensation,and Cu_2-xSe/g-C₃N₄heterojunction was prepared by in situ hot-injection method,and the photocatalytic performance and mechanism of the composite were explored.SEM,TEM and XPS analysis showed that Cu_2-xSe and g-C₃N₄were successfully combined together.The experiment of photocatalytic hydrogen production indicates that Cu_2-xSe/g-C₃N₄-10%exhibits the best photocatalytic hydrogen evolution property,and the H₂generation rate can reach 1954.92μmol·g^-1·h^-1,which is about 2.19times and 18.58 times compared with that of pure Cu_2-xSe and monomer g-C₃N₄,while showing good chemical stability.The improved photocatalytic energy is due to the increased light absorption intensity of the system,the effective separation and migration of photoinduced carriers and the synergy between the interface of Cu_2-xSe and g-C₃N₄,which facilitates the photocatalytic reaction.