Enhanced Photocatalytic Activity Of Bi Decorated Cu₂O?100?:a Density Functional Study

Copper oxide?Cu₂O?as a monovalent oxide of copper is a natural p-type oxide semiconductor with a direct band gap of 2.17 eV.It has attracted much attention of researchers in the field of gas sensors,solar cells,environmental management and photocatalysis due to its characteristics of low toxicity,environment-friendly and stable chemical properties.From the economic point of view,the price of cuprous oxide is low and the cost of production is low,so it is likely to realize large-scale industrial production to solve the problem of environmental pollution and energy shortage which have become the two major obstacles for the current social development.Therefore,the researchers have set foot on the search for clean and renewable energy journey.Solar energy is considered to be one of the most promising emerging renewable energy sources with its wide distribution,huge reserves,clean and sustainable.Photocatalytic technology based on inorganic semiconductor materials is considered to be one of the best ways using solar energy to improve energy and environmental problems.The ideal photocatalytic material should be able to make full use of visible light to produce hydrogen by splitting water.Conventional photocatalysts are mostly wide bandgap semiconductor metal oxides,which have poor response to visible light and low solar energy utilization.In theory,the cuprous oxide photocatalyst has a suitable bandgap and is capable of absorbing visible light.However,the desired visible photocatalytic activity has not be observed in experiments.Early in the 1970 s,people began the study of cuprous oxide,most research focused on the anti-fouling and cleanliness,until the late 1990 s began to study the photocatalytic performance of cuprous oxide.In 1998,Ikeda et al.reported that copper oxide decomposes water under sunlight to produce hydrogen and oxygen,which indicates the visible light photocatalytic performance of cuprous oxide.Subsequently,researchers in the theoretical calculation of the electronic structure of copper oxide found that the valence band of copper oxide and the bottom of the conduction band is mainly composed of copper atoms 3d and 4s orbit,which does notmeet the photo-excited electron transition angular momentum selection.This is the main reason for limiting the photocatalytic activity of cuprous oxide.To improve the photocatalytic activity,scientists have a lot of research on modification of copper oxide.The popular method is to use ion doping method to change its band edge structure,and promote visible light absorption.In fact,the surface of the photocatalytic material is the major site of the photocatalytic reaction,so the property of the material surface has a direct impact on the photocatalytic reaction.The development of nano-materials science and nanotechnology provides the possibility for the synthesis of various forms of cuprous oxide nanostructures.Polyhedral copper oxide nanomaterials exhibit boundless prospects.In particular,the surface dependence of polyhedral cuprous oxide nanocrystals has attracted wide attention of researchers.In this thesis,we have used the first-principles calculation based on the density functional theory to study the adsorption structure,electronic structure and optical properties of the bismuth adsorbed cuprous oxide?100?surface.Absorption energy calculations show that the bismuth atoms tend to adsorb on the surface oxygen vacancy and tend to individual dispersion instead of aggregate on the surface due to the lowest formation energy and larger distance between two Bi atoms at the surface than the Bi clusters,and moreover,the larger the adsorption concentration,more stable the absorbed system.The electron density of states calculations indicate that the adsorption of low concentration cannot eliminate the surface state,and the absorption of high concentration will introduce a new surface state.The surface coverage of around 25 percent can effectively eliminate the surface states and modify the band edges to satisfy the angular momentum selection rules for light excited transition of electrons,relative positions between the band edges and the redox potentials are suitable to photocatalytic hydrogen production from the redox water,and the optical absorption spectrum also indicates a positive response to visible light,implying that the Bi25@Cu₂O?100?is a promising visible light photocatalyst.