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First Principles Study on Doped Anatase Titania

Author: YaoXiaoJie
Tutor: YaoMan
School: Dalian University of Technology
Course: Materials Processing Engineering
Keywords: first principle TiO2 doping electronic structure photocatalytic activity
CLC: O614.411
Type: Master's thesis
Year: 2011
Downloads: 126
Quote: 0
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Abstract


Semiconductor photocatalysts appear to be a promising technology that has a number of applications in environmental systems such as air purification, water disinfection, hazardous waste remediation, and water purification. Titania (TiO2)-based photocatalysts have received intense attention as a promising photocatalytic material in photocatalytic and photo-electrochemical field for years. Many researchers have proved that TiO2 is the most preferable photocatalysts because of its physical and chemical stability, non-toxicity and ease of availability. However, as a wide band gap (WBG) semiconductor, anatase TiO2 (Eg=3.2 eV) can only be activated under ultraviolet (UV) irradiation (λ<387nm), which accounts for only about 5%of solar energy. To enhance the optical absorption in the visible range, great efforts have been made to modify the band gap of TiO2. In this paper, we studied the doping effects of some kinds of ions on the photocatalytic activity of anatase TiO2 from first principles calculation.At first, we studied pure anatase TiO2, the obtained structure parameters of pure anatase TiO2 calculated with DFT agreed well with the experiment data, which convinced us that our calculation is reliable enough to be used to analyse the electronic properties, such as band structure and density of states.For metal doping, we study the elements from Sc to Zn in period four and elements from Y to Cd in period five. The results showed that:compared with pure anatase TiO2, the electronic structure of TiO2 after most metal doping changed, which will affect its photocatalytic activity. The effects root in the d orbitals of doped metal ions, in this paper, we classified the doping metals according their effects on electronic structure of TiO2.Afterwards, we studied the photocatalytic activity of anatase TiO2 co-doped with Zr and N and anatase TiO2 co-doped with Zr and Ce. We also studied the photocatalytic activity of anatase TiO2 mono-doped with N, Zr and Ce. It is shown that the photocatalytic activity of N-monodoped TiO2 is more limited in the visible-light region as a result of the existence of N 2p gap states, while Zr-monodoping didn’t change the band gap of pure TiO2 and eventually didn’t exhibit better photo degradation ability in visible light region, Ce-monodoping only changed the band gap of anatase TiO2 from 3.14eV to 3.09eV. Addition of Zr to N-doped TiO2 brought the N 2p gap states closer to the valence band, enhancing the lifetimes of photo-excited carriers, while at the same time, lowering the edge of the conduction band, while Ce-N co-doped case narrows the band gap more significantly than the corresponding mono-doped anatase TiO2.From above, we come to the following conclusions:as to ion-doping, the effects of diminishing the band gap are the dominating factor that decides whether the absorption threshold wavelength of anatase TiO2 has a red shift or not. On the other side, ideal dopants should induce impurity energy levels in the band gap that are not too far away from conduction band or valence band, to avoid acting as recombination center of photo produced electrons and holes. All of this can give references when choosing doped ions henceforward.

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CLC: > Mathematical sciences and chemical > Chemistry > Inorganic Chemistry > Metal elements and their compounds > Section Ⅳ group metal elements and their compounds > The titanium Vice family ( IV B group metal elements) > Ti Ti
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