A simple particulate sol-gel route to synthesize nanostructural TiO₂-Ta₂O₅ binary oxides and their characteristics

Nanostructured and mesoporous TiO2-Ta2O5 films and powders with various TiO2:Ta2O5 molar ratios and high specific surface area (SSA) have been prepared by a straightforward particulate sol-gel route. Titanium isopropoxide and tantalum ethoxide were used as precursors and hydroxypropyl cellulose (HPC) was used as a polymeric fugitive agent (PFA) in order to increase the SSA. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that powders contained both hexagonal δ-Ta2O5 and monoclinic β-Ta2O5 phases, as well as anatase and rutile. It was observed that Ta2O5 retarded anatase-to-rutile transformation. Furthermore, δ → β phase transformation temperature increased with decreasing TiO2:Ta2O5 molar ratio. Transmission electron microscope (TEM) analysis also showed that Ta2O5 hindered the crystallisation and crystal growth of the powders. SSA of powders, as measured by Brunauer-Emmett-Teller (BET) analysis, was enhanced by introducing Ta2O5. TiTa11 binary oxide (TiO2:Ta2O5 = 50:50 molar ratio) annealed at 500 °C produced the smallest crystallite size (3.4 nm), the smallest grain size (15 nm), the highest SSA (172 m2/g) and the highest roughness. Atomic force microscope (AFM) analysis revealed that columnar-like morphology with nanosized grains was obtained for TiO2-Ta2O5 films. One of the smallest crystallite size and one of the highest SSA reported in the literature is obtained, and they can be used in many applications in areas from optical electronics to gas sensors.