Density Functional Theory Calculation On The Structure And Properties Of Metal Nitride Photocatalytic Materials

Because of the increasingly serious environmental pollution,developing clean energy becomes highly demanded all over the world.Researchers have carried out a lot of investigations on the mechanism of photocatalytic water splitting.The researches show that designing the structures of photocatalysts to adjust the properties can reduce the recombination of photogenerated electron-hole pairs and accelerate the surface catalytic reaction.There are many methods which have been adopted to enhance the photocatalytic performance,such as loading cocatalysts,constructing semiconductor heterostructures and so on.This dissertation focuses on the study of the structure and properties of metal nitride photocatalytic materials based on density functional theory（DFT）to explain the microscopic mechanism of photocatalytic water splitting process,and to provide a theoretical foundation for the experimental synthesis of highly efficient photocatalysts.The main chapters in the dissertation are as follows:The first chapter introduces the related background of the dissertation.The second chapter briefly presents the theoretical methods adopted,including the fundamental theorem of DFT,exchange-correlation functional and so on.The third chapter describes the DFT calculations of the photocatalytic reaction mechanism ofβ-Ge₃N₄ system loaded with RuO₂ nanoparticles.β-Ge₃N₄ is the first successful non-oxide photocatalystic system for overall water splitting in the ultraviolet region.According to experimental reports,RuO₂ nanoparticles act as a co-catalyst in the process of water splitting to produce H₂ and O₂ in theβ-Ge₃N₄ photocatalytic system.However,the photocatalytic reaction mechanism of this system is not clear.Loading cocatalysts is conducive to the separation of photogenerated electron-hole pairs and improves the photocatalytic performance of theβ-Ge₃N₄ system.The fourth chapter focuses on tantalum nitride（Ta₃N₅）,one of the promising materials for realizing overall water splitting in the visible light region.Theoretically,Ta₃N₅ meets the thermodynamic requirement of realizing overall water splitting,but it is found experimentally that Ta₃N₅ has a much stronger oxygen production capacity than hydrogen production capacity so that the photocatalytic overall water splitting cannot be easily accomplished.Recent experiments found that Ta₃N₅can selectively grow on the edge of KTaO₃ during the short nitridation process due to the novel precursors,which can achieve high charge separation.In order to reveal the reason for the the increased photocatalytic activity of Ta₃N₅/KTaO₃ system,we performed DFT theoretical calculations.It is found that the formation of the interface is beneficial to the separation of photogenerated carriers and effectively improves the efficiency of producing H₂ and O₂.The calculated results have reasonably explained the photocatalytic mechanism of the Ta₃N₅/KTaO₃ interface.The fifth chapter is related to the structural details and stability of the four possible Ta₃N₅ surfaces,with and without various single noble metal atoms（Rh,Pt,Ir,and Ru）by using DFT calculations.We investigate the most stable structures of the single-atom（Rh,Pt,Rh,and Ir）adsorbed on Ta₃N₅ surfaces,the electronic properties and hydrogen adsorption behavior of the Ta₃N₅ surfaces with and withoutadsorbed single metal atoms.Our restuls indicate that loading single metal atoms on the Ta₃N₅ surface can remarkably decrease the Gibbs free energy of HER compared to the clean ones.This study provides appropriate explanations for the high hydrogen production ability of the single-atom catalyst system.