Effect of Post-Heat Treatment on Physical Properties of Nanostructured TiO2 Powders Prepared by a Sol–Gel Method

Abstract

A nanostructured TiO2 powder was produced by a sol–gel method. The resultant powder was sintered at different temperatures ranging from 300°C to 800°C, for a constant time of 2 h. X-ray diffraction (XRD) results indicated that an increase in sintering temperature caused a transformation of the TiO2 powder from amorphous to polycrystalline. At temperatures lower than 500°C, a pure polycrystalline anatase phase was present, while a rutile phase was present at 800°C. A gradual transformation from the anatase to rutile phase occurred between 500°C and 800°C. A high-resolution transmission electron microscope (HRTEM) with selected area electron diffraction (SAED) capability was used to elucidate the shape and size of the particles as well as their electron diffraction. The TEM images displayed an increase in particle size from 20 nm to 90 nm when the sintering temperature was increased from 300°C to 800°C. The SAED patterns supported the XRD results. The diffuse reflectance data for the investigated samples were used to estimate their bandgap energy ($$ E_{\rm{g}} $$), which revealed that samples sintered at 500°C and 800°C had energy gap values of 3.18 eV and 3.01 eV, corresponding to pure anatase and pure rutile phases, respectively. Current–voltage (I–V) measurements were carried out on the sintered samples to calculate sample resistivity at room temperature. The results showed a slight increase in conductivity with increased sintering temperature up to 700°C, followed by a significant increase at 800°C.