Theoretical Design And Study Of Low-dimensional Multifunctional Materials

Due to the increasing global energy demand,continued reliance on fossil fuels for energy production and transportation,and population growth,the world is currently facing an energy crisis.The excessive burning of fossil fuels not only depletes finite natural resources but also leads to a yearly increase in CO2 emissions.Converting CO2 into fuels,chemical feedstocks,and other chemicals through redox reactions is a way to achieve carbon neutrality and turn carbon into a valuable resource.In addition,developing and utilizing green,non-polluting new energy sources such as converting renewable energy sources like solar energy into storable and transportable fuel energy,and achieving large-scale,low-energy consumption,and high stability through technological innovation can achieve the goal of replacing traditional fossil energy sources.In the past few decades,low-dimensional materials have attracted widespread attention in both CO2 reduction and new energy development.Due to quantum confinement effects,low-dimensional materials exhibit a wide variety of fascinating phenomena and unique physical and chemical properties,laying the foundation for many new applications.Although significant progress has been made in the study of low-dimensional materials,many challenges remain unresolved in basic scientific understanding and practical strategies for application.These challenges include the determination of 0D cluster structures,identification of active sites and catalytic processes in photocatalytic reactions,and the exploration of band engineering in 0D/2D heterojunctions.Therefore,the main objective of this paper is to focus on low-dimensional materials:using new computational tools to accurately describe the structure and electronic properties of Cu clusters at a low computational cost,exploring the photocatalytic mechanism of TiO2 surfaces,and designing Aun/TMDs heterojunction materials with high carrier separation efficiency.This article covers six chapters in detail,as described below.Chapter 1 introduces the research background,including the application of lowdimensional materials in energy and environment,as well as the concepts and development of 0D clusters and 2D semiconductor materials.Firstly,the global energy demand and the impact of energy on production and life are introduced.Then,the main challenges faced in energy use and their corresponding solutions are discussed,as well as the role of low-dimensional materials in addressing energy issues.Finally,the 0D clusters and their outstanding applications in alleviating environmental stress are detailed,as well as the unique advantages of photocatalysts TiO2 and 2D van der Waals heterojunctions in improving photocatalytic efficiency and energy conversion efficiency.Chapter 2 provides a brief description of the fundamental knowledge involved in computational quantum chemistry in this paper,including the development of density functional theory(DFT)and time-dependent density functional theory(TDDFT).Specifically,this chapter introduces the basic framework of DFT,the inference of important theorems,and common exchange correlation functional approximations.At the same time,this chapter introduces the Runge-Gross theorem in TDDFT,linear response density functional theory,and the minimal switching surface hopping method in nonadiabatic molecular dynamics.Finally,relevant software packages used in the computational process of this paper are briefly introduced.In Chapter 3,a global minimum energy structure search for the structure of Cun(n=10-50)clusters was performed by combining the global optimization algorithm and the deep learning potential energy model.The study obtained 35 cluster configurations with lower energy than the corresponding Cun structures included in the Cambridge Cluster Database.Based on the newly obtained cluster configurations,the chapter analyzes their structural evolution laws and basic physical properties.Additionally,the study selected three Cun clusters of different sizes(Cu13,Cu38,and Cu49,with sizes ranging from 0.86-1.22 nm)to investigate their electrocatalytic reduction of CO2.The results show that the main products of CO2 reduction by the three clusters are CO and H2,while the selectivity of hydrocarbons is suppressed.Chapter 4 investigates the thermal and photo-catalytic activation of C-H bonds during the dehydrogenation of C2H6 to C2H4 on the rutile TiO2(110)surface.Combining first-principles ground state and excited state calculations,it is shown that the photo-catalytic bond activation on the TiO2(110)surface is site-sensitive.Specifically,the C2H6 molecule is more likely to adsorb on the Ti5c site,where the reaction energy barrier for the ground state dehydrogenation process is lower than for the Obr site adsorption.In contrast,C2H6 adsorbed at the Obr site exhibits photoactivity at the initial adsorption,and the entire C-H bond activation process tends to occur in the excited state.During the C2H6 dehydrogenation process on both two adsorption sites of the TiO2(110)surface,the photo-generated electrons are always localized at the Ti4+ sites of the TiO2 substrate,while the photo-generated holes can be captured by the adsorbed C2H6 molecule to achieve the C-H bond activation.Chapter 5 designs 0D/2D Aun/TMDs van der Waals heterojunctions by loading Aun clusters with different sizes on the surface of monolayer transition metal dichalcogenides(TMDs).By changing the size of Aun clusters and the type of substrate TMDs,the bandgap of 0D/2D heterojunctions can be tuned to obtain different heterojunction types,including type Ⅰ,staggered type(type Ⅱ and S-scheme),and type Ⅲ heterojunctions,thus realizing a wide range of light absorption and utilization from the visible to near-infrared spectral range.Among them,Au20/MoS2 belongs to the S-type heterojunction,which can effectively achieve spatial separation of electrons and holes between materials and maintain strong redox capability.In addition to the potential application of the obtained staggered heterojunctions as photocatalysts,each type of heterojunctions is expected to achieve high-quality preparation and performance tuning of field-effect transistors.Chapter 6 provides a summary of the entire paper and proposes plans and prospects for future research.