First-principles Design And Calculation Of Novel 2D Materials In The Application Of Nitrogen Reduction And Hydrogen Purification

In recent years,atmosphere pollution and energy shortage brought about by the rapid economic development have been the main crises facing human society today.Research and development of efficient,cheap,green and highly stable catalysts are the important core technologies to solve the problems of atmosphere pollution and energy shortage.In the face of air pollution,we can find efficient exhaust gas purification systems.In the face of energy shortages,we can also design efficient energy storage conversion systems.Since the two-dimensional（2D）materials graphene was successfully synthesized,its unique physical and chemical properties have caused extensive research.We focus on exploring the value of the two-dimensional materials in the field of photocatalysis and hydrogen purification.With the rapid development of computer technology,theoretical technology has become a powerful tool for simulation.Some special phenomena of experiments and the physics-chemical properties of materials are explained by theory.In this thesis,the physical and chemical properties of the new 2D materials B@g-C₆N₆and P₂C₃are studied by first principles calculation methods,and their application potentials in the fields of photocatalysis and hydrogen purification are analyzed in depth.This thesis is divided into four chapters and the content is arranged as follows.In the first chapter,we give a brief introduction to the theoretical basis and calculation methods,and also present the used computational software package based on density functional theory.The second chapter introduce the research progress of several representative and popular 2D materials,and summaries the properties of 2D that are more common in experiments and theoretical calculations.Among them,the unique physical and chemical properties of 2D material graphene will be discussed.In addition,we also briefly introduce the properties and characteristics of common 2D materials such as graphene phase carbon nitride,black phosphorous,hexagonal boron nitride,and transition metal sulfides.The third chapter explores the catalytic activity of non-metallic B atoms doped on the g-C₆N₆monolayer for the reduction of N₂to NH₃.We found that the B@g-C₆N₆system can effectively capture and activate N2 molecules though the“acceptance-donation”electron transfer process.B atom doped g-C₆N₆can greatly improve the absorption of visible and infrared light,which makes the system become an ideal candidate for N₂fixation under visible light.Low initial potential,strong absorption of visible light,easy synthesis and high thermal stability,these characteristics make B@g-C₆N₆a high performance photocatalyst with fixed N₂.This also provides a new and efficient method to promote the sustainable production of NH₃.In the last chapter,based on density functional theory,we give a calculation and molecular dynamics simulations.We study the diffusion rate and selectivity of porous P₂C₃membranes for different gases including hydrogen（H₂）,carbon monoxide（CO）,nitrogen（N₂）,carbon dioxide（CO₂）,methane（CH₄）.We find that the diffusion barrier of H2 through the film is as low as 0.18e V,while the diffusion barrier of other gas molecules are higher than 0.5 e V,indicating that H₂and other gases can be further efficiently separated.At room temperature,the P₂C₃membrane has a high permeability.When the mechanical strain on the porous P₂C₃membrane is increased to 6%,the permeability can reach 2.22×10⁷GPU.Therefore,we can predicted that in terms of H₂selectivity and permeability,P₂C₃porous membranes have unlimited potential in the field of hydrogen purification.