First-principles Study Of Fe-N Doped Anatase TiO₂and Surface Adsorption Of NO Properties

TiO₂has attracted considerable attention in recent years due to its photocatalyticdegradation activity of organic compounds, Anatase TiO₂is more efficient than rutilefor catalysis, photocatalysis. First principles method has been used in this paper to studythe defects in bulk anatas TiO₂and anatase TiO₂（101） surface adsorption of NO.This article is divided into eight chapters. In the first and second parts of chapter1,we introduced the basic idea of density functional theory, form original Thomas-Fermimodel, Hohenberg-Kohn theorem, to Kohn-Sham equation. Then we gave a briefintroduction of some DFT based simulation packages used in the following work, suchas CASTEP.The third and fourth chapters describe the band structures, density of states, chargepopulation and optical properties of pure, Cr-doped and Mn-doped anatase-phase TiO₂.The analysis showed that there are three new impurity bands located in the middle ofband gap in Mn-doped TiO₂. The impurity bands formed mainly by the O-atom2porbital and the Mn-atom3d orbital hybridized together.The Cr-doped TiO₂produced anew band near the bottom of conduct band. The impurity band was composed of theO-atom2p orbital and the Cr-atom3d orbital hybridized together. Because of theemergence of impurity level, the band gap became smaller.It is theoretically predictedthat Cr-doped and Mn-doped anatase-phase TiO₂would lead to the red shift ofabsorption wavelength and the increase in coefficient of light absorption. A newabsorption peak in the low-energy region, corresponding to energy0.9eV has beenfound experimentally in Cr-doped anatase-phase TiO₂. A peak corresponding to energy0.8eV has been found experimentally in Mn-doped. This theory conclusion was thesame with the experiment.In the fifth chapter, the analysis from the band structure, density of states andoptical properties showed that the Fe-N co-doping generated two layers energy bands inthe forbidden band gap. One layer impurity bands mainly formed by the N-atom2porbital and the Fe-atom3d orbital hybridized together, the other impurity band mainly was composed of the Fe-atom3d orbital. Due to the emergence of impurity level, theband gap became smaller. It was theoretically predicted that Fe-N co-dopedanatase-phase TiO₂would cause the red shift of absorption wavelength and the increasein coefficient of light absorption. There was a new absorption peak in the low-energyregion, corresponding to energy was1.0eV. This theory conclusion was the same withthe experiment.The sixth chapter describes the structure, the surface energy, the band structure,density of states and charge population of anatase TiO₂（101） surface The analysisshowed that anatase TiO₂（101） crystal surface structure which the outermost and secondlayer respectively terminated by twofold coordinated oxygen atoms and fivefoldcoordinated titanium atoms was much more stable. The surface energy of18layersmodel was0.580J/m2. The surface electronic structure was similar to bulk’s, and therewas no surface state. Compared to the surface of the bulk, band gap increased0.36ev.TiO₂（101） surface has not absorbed in the low energy region. An absorption edge in theultraviolet region, corresponding to energy2.7eV, has been found.The seventh chapter describes NO is not easily adsorbed on the surface which theoutermost terminated by twofold coordinated oxygen, and is easily adsorbed on thesurface of the presence of O vacancy defects, the high concentration of O vacanciescontribute to the adsorption of NO.The eighth chapter gives a conclusion of the whole paper,and the prospectsresearch space of this subject in the future.