Preparation and characterisation of nanostructural TiO2–Er2O3 binary oxides with high surface area derived from particulate sol–gel route

Abstract

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 (TiO2−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 (1·2 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.