| As we all know,with the rapid development of modern industry,traditional energy sources,such as coal,petroleum,and natural gas,are in danger of depletion.And the large-scale utilization of these traditional energy sources also brings huge pollution to the environment,such as greenhouse effect,acid rain,hase and so on.Solving energy and environmental issues has also become a major demand in China.All of these urgently require us to develop and make full use of renewable energy,which includes tidal energy,wind energy,geothermal energy,and solar energy.Among these renewable energy sources,solar energy is considered to be the most promising source of energy because of its geographical diversity and energy richness.How to make full use of solar energy more efficiently and efficiently has become one of the most popular scientific research directions.Fortunately,in the 1972,Japanese scientists Fujishima and Honda discovered photocatalytic water-splitting on the TiO2 electrode.It opens a new chapter in the transformation and use of solar energy by humans.Photocatalytic technology can use sunlight to split water into hydrogen,or convert carbon dioxide into ethanol.This technology not only uses sunlight as a driving force for photocatalytic reactions,but also converts solar energy into clean energy such as hydrogen.After hydrogen being used,the product is water,which can reused to produce hydrogen through solar energy,and nd the process can be recycled.The conversion of CO2 is a process that turns waste into treasure.It not only alleviates the greenhouse effect of CO2,but also turns into chemical energy that is conveniently stored,such as methane and ethanol.Therefore,photocatalytic technology has great application prospects in the development of new energy sources and the treatment of environmental pollution.The carrier of photocatalytic technology is photocatalytic materials.Therefore,the development of photocatalytic materials has become the key to the effective use of solar energy.However,during the research and development of photocatalytic materials,the method widely used by experimenters is the trial-and-error model,that is,through repeated experiments to synthesize different photocatalytic materials,and then measure their performance to select the materials.It has caused a long period of development of new photocatalytic materials,and increased the cost.In addition,these waste products will cause the environment pollutants.It urgently requires us to find a more convenient and environmentally friendly way to develop new photocatalytic materials.Fortunately,the rapid development of quantum chemistry methods and supercomputer technology facilitates us to use theoretical methods to design photocatalytic materials.Therefore,the experimental synthesis based on the theoretical design has become the most efficient method for the development of new materials.Due to its wide bandgap,semiconductor materials can absorb sunlight and are often used as photocatalysts.The photocatalytic process on the surface includes charge transfer,energy transfer and material transformation.The core of these complex processes the electronic state motion.Then,understanding the movement of electronic states is crucial to the design of the material.At the same time,we know that the Schrodinger method is an advantageous tool for obtaining electronic information and provides guidance for the design of photocatalytic materials.However,because the mathematical problem in the Schrodinger equation is too large to solve,the electron density functional theory based on the KS equation simplifies the calculation process,shortens the calculation time,and facilitates us to calculate the periodic structure.In this paper,electron density functional theory is used to simulate and design new functional photocatalytic materials.This paper is divided into six chapters to illustrate the structure-activity relationship between electronic information and material design.The first chapter mainly introduces the background,reaction mechanism,research status and development prospects of photocatalysis.The photocatalytic reaction on the surface of composite semiconductor materials is a complicated process.Then there are many factors affecting the photocatalytic reaction,and it is worth in-depth exploration.First of all,how to improve the light absorption of the material itself and the utilization of absorbed photons is important to design materials.However,traditional photocatalytic materials cannot be well represented in these two aspects,which promotes the development of new composite photocatalytic materials.We construct mental-semiconductor heterojunction,p-n heterojunction to tune the band alignment of composite materials,improving the photocatalytic properties of the material.Second,the active sites on the surface are constructed to increase the interaction between the surface and the reactants.The subsurface oxygen vacancies are a very good example and will be introduced in detail in Chapter 5 of this paper.In chapter 2,we briefly introduce the first principles,some common approximate methods for solving the Schrodinger equation,and application and development of density functional theory(DFT).The DFT is based on quantum mechanics,and particle density is the basic variable instead of the wave function.It mainly reduces the multi-particle problem to the single-particle problem by the Kohn-Sham equation,and all the approximations in the system are placed in exchange-related functionals to solve the charge density of the ground state of the system,and then obtain the basic properties of the system.In the actual calculation process,we need to select the right exchange-related functionals based on the characteristics of the research object and the purpose of the research.Subsequently,we have conducted a series of studies about the relationship between the charge polarization of the interfaces,subsurfaces,and surfaces and properties of photocatalytic materials.This part is mainly discussed in chapter 3,4,5 and 6.In chapter 3,we mainly studied the interfacial polarization of metal-semiconductor heterojunction how to tune the band alignment of the photocatalytic material.A first-principles study is performed to propose and demonstrate a novel stragey toward convenient energy band engineering in metal/semiconductor hybrids.In this design,a metallic nanoparticle(M)is interfaced with a type-? binary heteronanostructure(S1-S2).The calculatedresults indicate that the conversion from the straddling gap(type ?)of S1-S2 heterojunction to the staggered gap(type ?)of S1-(S2/M)ensures well-steered collections of electrons at the surface of the exposed nanorod stem and holesat the metal surface of the node sheath.In the ternary architecture of S1-(S2/M),the work function difference would drive free electrons to flow from M to S2 so as to level up the energy bands of S2,and eventually achieve the type-?-to-type-? conversion.In chapter 4,we designed the composite photocatalytic material that absorbs the full spectrum of sunlight,and explored the influence of the interfacial polarization of the p-n heterojunction about band alignment of the material.The full harvest of solar energy by semiconductor in light conversion requires such a material to simultaneously absorb diverse spectrum ranges of solar radiation and collect photo-generated electron and hole charges separately.We designed the ZnS-CdS-Cu2-xS heterostructure so as to realize full-spectrum absorption of solar energy.Here the localized surface plasmon resonance(LSPR)of nonstoichiometric copper sulfide Cu2-xS nanostructures enables effective NIR absorption.More significantly,the construction of p-n heterojunction between Cu2-xS and CdS forms staggered gaps.Such band alignment enables well-steered photo-generated carriers flow for electron-hole separation in the ternary system and hence efficient solar energy conversion.In chapter 5,we mainly designed a reaction site with high stability and high catalytic activity.As we all know,TiO2 material is widely-used in photocatalytic water-splitting.Surface defects of oxygen vacancy in TiO2 provide sites with high photocatalytic activity,while its photocatalytic stability is often undermined because of the trapping of oxygen species.Here we conducted a theoretic study to propose the use of subsurface defect of oxygen vacancy in anatase TiO2(101)for photocatalytic water-splitting,to combine both high activity and stability.It is demonstrated that subsurface defects expand light harvesting ability of TiO2 to visible light region,and facilitate photo-generated charge separation,which were verified by experimental test results.It also bestows high catalytic activity on the above non-defective surface sites for water adsorption and oxidation.Importantly,subsurface defects are untouchable to reactive oxygen species,ensuring high stability for the nearby surface catalytic sites.These demonstrate the role of subsurface oxygen vacancies in catalyzing oxygen evolution reaction,leading to new design strategy for photocatalytic or catalytic oxide materials.In chapter 6,we develop highly selective sites for photocatalytic conversion of CO2 to CH4 by isolating Cu atoms in Pd lattice.Photocatalytic conversion of CO2 to CH4-a carbon-neutral fuel represents an appealing approach to remedy the current energy and environmental crisis.However,it suffers from the large production of CO and H2 by side reactions.The design of catalytic sites for CO2 adsorption and activation holds the key to address this grand challenge.According to our theoretical simulations,the isolation of Cu atoms in Pd lattice can play triple roles in the enhancement of CO2-to-CH4 conversion:(1)providing the paired Cu-Pd sites for the enhanced CO2 adsorption;and(2)elevating the d-band center of Cu sites for the improved CO2 activation.This work provides fresh insights into the catalytic site design for selective photocatalytic CO2 conversion,and highlights the importance of catalyst lattice engineering at atomic precision to catalytic performance. |
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