The Application Of Defect-based Electronic Structure Regulation In Photocatalysis

In recent years,due to the excessive development and overdraft of fossil fuels,human society is facing energy crisis and environmental pollution problems.Therefore,new environmentally friendly energy sources are needed to accelerate the research for realizing the sustainable development of human society in a green and safe manner.In the field of energy-related research,semiconductors are widely used as raw materials to convert solar energy into clean energy,which has been regarded as an effective means to solve the aforementioned severe problems,and has been extensively explored by researchers.In the past ten years,the booming two-dimensional nanomaterials have received high attention because of their special electronic structure and ease of operation.It has brought the possibility of achieving a substantial increase in the photocatalytic efficiency of semiconductor materials.In this article,based on two-dimensional nanomaterials,various operating methods were carried out to control the electronic structure of two-dimensional nanomaterials,like surface modification,doping,introducing vacancy defects and other operating methods of photocatalysts to establish appropriate research models,and then jointly explored the reaction mechanism behind the regulation through experiments and theoretical calculations,to provide some guidance and assistance in the research field,industrial production and practical applications for the preparation of high-performan ce two-dimensional nanomaterial photocatalysts.The main content of this paper includes the following aspects:1.The iron-doped bismuth tungstate two-dimensional nanosheet photocatalyst was successfully prepared by the ordinary hydrothermal method.At the same time,a certain amount of oxygen vacancy was introduced into the bismuth tungstate two-dimensional nanosheets through the substitution of iron atoms,which greatly promoted the photocatalytic water oxidation performance.The oxygen production rate can reach 131.2 μmol g-1 h-1 under visible-light driving and environmental conditions,which is more than three times that of pure bismuth tungstate two-dimensional nanosheets.The reason is that after iron doping,the bandgap of the catalyst became narrower,and at the same time,the position of the top of the valence band became more positive,which enhanced the visible-light absorption of the photocatalyst and the ability of photo-generated holes to be oxidized.A specific iron doping concentration can introduce a large number of oxygen vacancies,and the local electron distribution changed around the oxygen vacancies,resulting in a rapid charge transfer channel between the oxygen vacancies and adjacent metal atoms,realizing accelerated photo-generated carrier transfer.The iron dopants and oxygen vacancies in the crystal lattice synergistically promoted the separation of photo-generated holes and photo-generated electrons,so that more photo-generated holes can effectively participate in the photocatalytic water oxidation reaction.In addition,iron-doped bismuth tungstate two-dimensional nanosheets show excellent durability in an aqueous environment and have great potential in practical applications.Therefore,this kind of transition metal-doped two-dimensional nanomaterial has high potential application value and is worthy of further investigation.2.The lanthanide single-atom-doped bismuth oxychloride two-dimensional nanosheet photocatalyst was successfully synthesized by the ordinary hydrothermal method,and the photocatalytic nitrogen reduction and ammonia production were greatly improved compared to the pure bismuth oxychloride two-dimensional nanosheet.The single-atom cerium-doped bismuth oxychloride two-dimensional nanosheets achieved an ammonia production rate of 19.4 μmol g-1 h-1 without adding any sacrificial agent and cocatalyst,which is higher than that of pure bismuth oxychloride two-dimensional nanosheets by nearly three times.The structural advantage of the single-atom catalyst determines that it has better light absorption performance than the pure counterpart.For the role of 4f electrons in the photocatalytic process,it can be considered that the active 4f electrons in the single-atom-dispersed cerium atoms could act with the two-dimensional bismuth oxychloride nanosheets substrate to give rise to fast charge carrier transfer.These interactions increased the conductivity of the catalyst while inhibiting the recombination of photogenerated carriers,which greatly improved the efficiency of photocatalytic ammonia production.This work guides the development of various electronic structure control methods to obtain better photocatalytic nitrogen reduction performance.3.A pothole-rich tungsten trioxide ultrathin nanosheet photocatalyst was synthesized using a chemical topology conversion strategy,which can activate the nitrogen-nitrogen triple bond of nitrogen molecules and convert them into nitrate under ambient conditions.Among them,the average nitrate generation rate obtained by using pothole-rich tungsten trioxide ultrathin nanosheets as a catalyst is 1.92 mg g-1 h-1,which is 9.8 and 16.5 times of the performance of pothole-free tungsten trioxide ultrathin nanosheets and bulk tungsten trioxide,respectively,indicating that the potholes have a significant effect on improving the performance of photocatalytic nitrogen oxidation to produce nitrate.The rich pothole structure can provide abundant anchor points for the direct adsorption and subsequent activation of nitrogen molecules.At the same time,the pothole structure also helps to transfer the high momentum electrons in the catalyst during the photocatalytic reaction process to form more electron-hole pairs to participate in the photocatalytic nitrogen oxidation reaction,which can further accelerate the activation and cleavage of nitrogen-nitrogen triple bonds.This strategy also provides important insights into many other light-induced chemical bond activations in photocatalytic reactions,such as carbon dioxide reduction reactions and water splitting reactions.