Preparation and characterisation of nanostructural TiO2–Ga2O3 binary oxides with high surface area derived form particulate sol–gel route

Abstract

Nanostructured and nanoporous TiO2–Ga2O3 films and powders with various Ti:Ga atomic ratios and high specific surface area (SSA) have been prepared by a new straightforward particulate sol–gel route. Titanium isopropoxide and gallium (III) nitrate hydrate 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 rhombohedral α-Ga2O3 and monoclinic β-Ga2O3 phases, as well as anatase and rutile. It was observed that the Ga2O3 formed from the nitrate precursor retarded anatase-to-rutile transformation. Furthermore, transmission electron microscope (TEM) analysis also showed that Ga2O3 hindered the crystallisation and crystal growth of powders. SSA of powders, as measured by Brunauer–Emmett–Teller (BET) analysis, was enhanced by introducing Ga2O3. Ti:Ga = 50:50 (at%/at%) binary oxide annealed at 500 °C produced the smallest crystallite size (2 nm), the smallest grain size (18 nm), the highest SSA (327.8 m2/g) and the highest roughness. Ti:Ga = 25:75 (at%/at%) annealed at 800 °C showed the smallest crystallite size (2.4 nm) with 32 nm average grain size and 40.8 m2/g surface area. Ti:Ga = 75:25 (at%/at%) annealed at 800 °C had the highest SSA (57.4 m2/g) with 4.4 nm average crystallite size and 32 nm average grain size. 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.