Theoretical Study On The Interface Structure And Properties Of Precious Metals And Their Oxides And Titanium Dioxide Heterojunction

With the rapid development of the world economy,the depletion of fossil energy and the continuous deterioration of the environment have become an important factor restricting the development of human society.Semiconductor photocatalytic technology can not only make use of solar energy to convert clean energy,but also can degrade pollutants.As one of the most promising technologies to solve the current energy crisis and environmental pollution,titanium dioxide is one of the most widely studied photocatalysts as the representative of traditional photocatalytic materials.It still has the limitations of the material itself.The synthesis process of noble metal supported on TiO₂ and its related photocatalytic properties are reported.The conclusions are based on the reaction products to speculate the reaction mechanism.Due to the presence of a small amount of noble metals,it is difficult to analyze and study the microstructure by means of characterization.The theoretical calculation method can make up for these shortcomings by comparing the noble metal supported systemically,and the annealing treatment in the noble metal supported may lead to the appearance of the transition layer including the solid solution and the noble metal oxide structure.The role of these structures in the loading of noble metals is worthy of further study.In summary,the role of noble metal oxidation and solid solution in these transition layers is systematically studied.The main research contents and conclusions are as follows:?1?In this article,the electronic structures,density of states and interfacial relaxation are discussed to provide an unambiguous micro-structures of the interface for fcc-metal?111??metal=Rh,Pd,Ag,Ir,Pt and Au?/anatase TiO₂?101?and hcp-metal?001??metal=Ru and Os?/anatase TiO₂?101?hetero-structures.The interface of micro-structures affects the distribution of space charge which is bound to produce electric dipole moment along the normal direction of the interface.Moreover,a strong built-in electric field generated by interfacial electron transfer leads to the efficient separation of photo-generated carriers and band bending.The built-in electric field at the interface is also the main driving force for separation of photo-generated carriers.Furthermore,noble metal/titanium dioxide hetero-structures demonstrate upward band bending.The electronic wave function of Pd-4d or Pt-5d state can extend to the band gap of the interface layer TiO₂ which make the interface layer TiO₂ metallized.That favorable interface state can reduce the Schottky barrier height,which means that the electron-excited transitions just need lower energy.?2?It is reported that there are metal oxides in noble metals supported on titanium dioxide after annealing.However,the larger lattice mismatch at the interface often induces unfavorable interfacial states that can act as recombination centers for photo-generated electron-hole pairs.If the hetero-structure's components have the same crystal structure,this disadvantage can be easily avoided.Both noble metal oxides and titanium dioxide have rutile crystal structure.Therefore,the interfacial properties of hetero-structures composed of a noble metal dioxide and TiO₂ with a rutile crystal structure have been systematically investigated using first-principle calculations.In particular,the Schottky barrier height,band bending,and energy band alignment are studied in order to demonstrate whether formation of the noble metal oxide transition layer in the noble metal loadong affects the photocatalytic performance.In all cases,no interfacial states exist in the forbidden band of TiO₂,and the interfacial formation energy is very small.A strong internal electric field generated by interfacial electron transfer leads to the efficient separation of photo-generated carriers and band bending.Because of the differences in the atomic properties of the components,RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures demonstrate band dividing,while RhO₂/TiO₂ and IrO₂/TiO₂ hetero-structures have a pseudo-gap near the Fermi energy level.Furthermore,NMO₂/TiO₂ hetero-structures show upward band bending.Conversely,RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures present relatively strong infrared light absorption,while RhO₂/TiO₂ and Ir O₂/TiO₂hetero-structures show an obvious absorption edge in the visible light region.Overall,considering all aspects of their properties,RuO₂/TiO₂ and OsO₂/TiO₂ hetero-structures are more suitable than the others for improving the photocatalytic performance of TiO₂.?3?In the study of solid solution materials,complex electron correlation and non-equilibrium atomic interaction as primary factors is influence the macroscopic structure and properties of solid solution.Hence,this work is concentrate to study the corresponding electronic structure and properties of Ru_1-xTi_xO₂ solid solution by using density functional theory.From the calculated results,the convincing interaction parameter between TiO₂ and RuO₂ is based on the most stable supercell model.Using the subregular solution model,the enthalpy of mixing can be represented by the expression,?₁)/·8)7)^-1=(3₄2)(3₂(35.30(3₄2)+23.08?3₂?.The calculated phase diagram is more reliable because it is consistent with the results of others'experiments.The existence of metastable phase Ru-rich solid solutions is less than 0.27 and for metastable phase Ti-rich solid solutions of minimum solubility is 0.81 at 1698 K temperature.The electron density of Ru_1-xTi_xO₂ solid solutions at Fermi level has a stronger dependence on substitution composition of Ru atom.From the data of electronic structure and optical properties,the solid solutions of lower and higher component Ti atoms support the potential advantages of its application in electrochemical and photocatalytic materials.?4?Solid solution structure composite semiconductor has been extensively studied because of their role in photocatalysis.The present work studied the interfacial structures and the electronic structures of rutile-type Ru_1-xTi_x O₂/RuO₂ and Ru_1-xTi_xO₂/TiO₂hetero-structures using first-principles calculations.It is found that the Ru_0.75Ti_0.25O₂/TiO₂heterostructure has very small lattice mismatch,slight atomic relaxation and low interfacial formation energy.The average electron density difference shows that interface electrons transfer from solid solution to RuO₂ or Ti O₂.It also shows that electrons in solid solution are mainly transferred to the bridged oxygen atoms at the interface.And the interface of Ru_0.75Ti_0.25O₂/TiO₂ heterostructure has more electron transfer quantity,which means that stronger built-in electric field could be generated at the interface.According to the direction of charge transfer,the band bending of TiO₂ in solid solution and TiO₂heterostructure is proposed.The existence of a small amount of solid solution at the interface of RuO₂/TiO₂ heterostructure is unfavorable to the separation of interface charge.Therefore,the annealing of RuO₂/TiO₂ avoids the formation of solid solution structure as far as possible.When the solid solution of Ru_0.75Ti_0.25O₂,RuO₂ and TiO₂ formed the interface with each other,the photocatalytic quantum efficiency can be improved by more efficient separation of photogenerated carriers.