Estudo Químico-Quântico do Óxido Ti(1-x)CexO2-δ na Fase Anatase

• Ano de defesa: 2014
• Autor(a) principal: Albuquerque, Anderson dos Reis
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal da Paraí­ba; BR; Química; Programa de Pós-Graduação em Química; UFPB
• Palavras-chave em Português: TiO2; Dopagem com cério; Defeitos pontuais; Modelos periódicos; Anatase; Ce-doping; Point defects; Periodic models; CIENCIAS EXATAS E DA TERRA::QUIMICA
• Link de acesso: https://repositorio.ufpb.br/jspui/handle/tede/7154

Titanium dioxide (TiO2) in anatase phase has been the most studied metal oxide in the last two decade due to its potential technological aplication in many areas, such as dyes, (photo)catalysts and solar cells. Computational and experimental methods has been employed to understand the mechanical, electronical and catalytic properties of anatase. In this context, the introduction of dopants and induction of point deffects formation (mainly oxygen vacancies) are responsible for tunning those properties in many situatuions, e.g. increasing the (photo)catalytic efficience. In the present study, we investigated the effect of Ce-doping on the formation of oxygen vacancy and reduced Ti3+ and Ce3+ centers in anatase TiO2 (bulk and (001) surfaces) by means of computational quantum chemical calculations. All calculations were performed at the density functional theory (DFT) level taking into account the periodicity of the systems. The bulk phase was initially studied without dopant, and the Grimme DFT-D2 dispersion potential was reparameterized for octahedral [TiO6] interaction in anatase polymorph within the B3LYP (GTO) approach (hereafter named B3LYP-D*). Several properties were calculated from bulk with B3LYP-D* in good agreement with experimental values from anatase single crystals, such as: Wulff construction of single crystal in thermodynamic equilibrium, elastic constants, infrared and Raman vibrational frequencies, and electronic structure calculations (band structure and density of states). Two DFT approachs were used for mitigate the self-interaction error (SIE) in both reduced and/or Ce-doped systems: the on-site Dudarev DFT+U correction and the hybrid B3LYP (20% HF) functional with plane-wave or Gaussian-type basis set. Only a small local perturbation was associated with the Ce-dopant introduction in the octahedral site (bulk) and Ce(5c) (surface). The Ce-doped systems presented lower oxygen vacancy formation energy than pristine TiO2. The most stable VO configuration in the bulk were in the next neighbors from the reduced [CeO6]/ center, instead the low-coordinated [CeO5] centers. Similarly, the dopant on the subsurface distoted octahedral [CeO6]d site of (001) surface boosted the remotion of O(2c) in the outmost layer of the surface. This behavior was not observed with the dopant on the low-coordinated [CeO5] site. The Ti3+ [3d 1] and Ce3+ [4f 1] midgap states were found up to ~ 1.0 eV bellow de conduction band. These founds are in agreement with experimental evidences of the enhanced facilitation of VO formation in Ce-doped anatase, and superior (photo)catalytic activity when compared with undoped TiO2. In the general way, the vacancy formation energy decreased significantly in the following situations: (i) oxide reduction in the presence of Ce as dopant; (ii) VO in the nearest neighbor sites of the reduced [CeO6]/ octahedra (iii) introduction of two Ce dopants around VO; (iv) VO in the outmost layers plus [CeO6]/ at the subsurface.