Preparation and characterisation of nanostructural TiO 2 –Er 2 O 3 binary oxides with high surface area derived from particulate sol–gel route

Nanostructured and nanoporous TiO₂–Er₂O₃ films and powders with various TiO₂ : Er₂O₃ molar ratios and high specific surface area (SSA) have been prepared by a new straightforward particulate sol–gel route. X-ray diffraction and Fourier transform infrared spectroscopy revealed that erbium oxide formed in the range 50–100 mol.-%Er₂O₃, whereas erbium dititanate formed in the range 25–100 mol.-%Er₂O₃. Oxygen deficient titania phases (TiO_2−x), such as Ti₇O₁₃ and Ti₂O₃, were observed for TiO₂ : Er₂O₃=25 : 75 (molar ratio) system annealed at 800°C. It was observed that Er₂O₃ retarded anatase to rutile transformation. Furthermore, TEM analysis also showed that Er₂O₃ hindered the crystallisation and crystal growth of powders. Specific surface area of powders measured by Brunauer–Emmett–Teller analysis was enhanced by introducing Er₂O₃. TiO₂ : Er₂O₃=25 : 75 (molar ratio) system annealed at 500°C produced the smallest crystallite size (1&middot2 nm), the smallest grain size (17 nm), the highest SSA (174 m² g⁻¹) and the highest roughness. TiO₂ : Er₂O₃=50 : 50 (molar ratio) system annealed at 800°C showed the smallest crystallite size (4·3 nm), the highest SSA (44 m² g⁻¹), the highest roughness with 32 nm average grain size. One of the smallest crystallite sizes and one of the highest SSA reported in the literature are obtained, and they can be used in many applications in areas from optical electronics to gas sensors.