The Structure And Characteristics Of Photocatalytic In TiO₂:the First Principle Study

As the global depletion of energy such as coal, oil, and the greenhouse effect, acid rain andhaze caused by the increasingly serious environmental problems, development and utilization ofrenewable energy, effective control and treatment of environmental pollution have become themajor issues facing the world and to be resolved. Solar energy and hydrogen energy with theirenvironment-friendly and sustainable use and other characteristics are considered to be one of theworld’s major sources of energy in the future. In1972, Japan Fujishima and Honda reported waterin light irradiation on TiO2electrode spontaneously decompose and produce hydrogen. Catalyticactivity of TiO2for its high resistance to corrosion, low costs were extensively studied by scientists.However, as the ideal semiconductor photocatalytic materials, the application of TiO2is severelyconstrained because of its wide band gap (3.2eV). In this thesis, we use the spin-polarized densityfunctional theory by using Quantum Espresso and VASP simulation codes, calculate and analyzethe influence on the electronic structure and optical properties of TiO2after codoping the transitionmetal and nonmetal as well as nonmetal codoping. We find that non-metallic C/N and transitionmetals Re doping has lower defect formation energy and higher binding energy, which caneffectively change the band edge thus to enhance the efficiency of TiO2photo-splitting water.Moreover, we find that stress and hole has a very significant effect on nonmetal doping system.When the dopant complex on neighboring oxygen sites contains a large radius atom, and the dopedsystem has at least one net hole, the dopants will strongly couple to form a pair through the locallattice strain induced by the large dopant. The coupling results in bandgap narrowing due to theappearance of the fully occupied mid-gap states, leading to a much more effective band gapreduction than that induced by mono-doping or conventional donor-acceptor codoping. Thecalculated absorption spectra show that acceptor-acceptor codopings could shift the absorptionedge to the visible light region. We propose a hole-strain-mediated coupling mechanism betweenco-doped acceptors in anatase TiO2. Using both the new mechanism and the double holes mediatedcoupling mechanism, could better explain the underneath mechanism for the red-shift of opticalabsorption spectra caused by the acceptor-acceptor codoping in TiO2.