Structural, Electronic And Optical Absorption Properties Of TiO₂Nanotube Adsorbed With Cu, Ag Or Au Clusters

The titanium dioxide nanotube(TiO2NT) material with noble metal particles deposited on the surface is potentially valuable in realizing much advanced functionality. It can not only enhance the separation of electron-hole pairs, but also alter the energy band structure of TiO2NT, expanding the optical absorption region to longer wavelengths. In this thesis, TiO2NTs were constructed from the (101) surface of anatase TiO2and Mn/TiO2NT systems which TiO2NTs were adsorbed with noble metal clusters Mn (where n=1-4and M denotes Cu, Ag or Au), have been investigated based on first-principle calculations. The stability, electronic structures and optical absorption properties of these adsorption systems have been systematically analyzed. The main results obtained are summarized as below:1. The theoretical TiO2NT models were successfully constructed. TiO2NTs of two chiralities,(6,0) and (0,3), were constructed by rolling up the (101) surface of anatase TiO2along different directions. The calculated electronic structures revealed that the band gap of the (6,0) TiO2NT is direct, while that of the (0,3) TiO2NT is indirect.2. After geometric structure optimizing, the ground-state structures of the adsorption systems Mn/TiO2NT have been identified through comparing the average values of adsorption energy. Cun clusters and Agn clusters share common adsorption law that the values of their average adsorption energies show odd-even oscillations; while Aun clusters exhibit different adsorption behaviors.3. The electronic structures of the ground-state Mn/TiO2NTs have been calculated.The results indicated that the adsorption of noble metal cluster can lead to a shift of the Fermi level, as well as introduce impurity states into the band gap and valence band of the TiO2NT. The impurity states can reduce the energy needed for electron transition and bring obvious redshift of absorption edge for the TiO2NT, leading to enhanced visible light responsivity. Further more, the impurity states can enhance the separation of electron-hole pairs, improving the photocatalytic ability of TiO2NT. In addition, the increase of the density of state around the valence band top can also raise the possibility of electron transition, which is likely to make contribution to the enhancement of light absorption intensity of the TiO2NT.4. The optical absorption properties of the ground-state Mn/Ti02NT systems have been further calculated. In all cases, the optical absorption spectra are inclined to expand to the region of longer wavelength, with increased absorption intensity. Among the three kinds of Mn clusers, Cun cluster adsorption produces the best overall performance of visible light absorption for the TiO2NT. For the same kind of Mn clusters with different size, M4cluster adsorption corresponds to the best absorption properties of the TiO2NT.