Sol-gel nanostructured titanium dioxide: Controlling the crystal structure, crystallite size, phase transformation, packing and ordering

The anatase phase of titania was stabilised with physically modifying particulate sol-gel process. Two major parameters, peptisation temperature and drying temperature, were identified which were responsible for retarding the anatase to rutile phase transformation, crystal growth and packing of primary particles. The critical nucleus size of transformation was controlled by natural (at 25 °C) and artificial (at 50 and 70 °C) peptisation techniques. Moreover, sintering of primary particles was controlled by cool (at 0 and 5 °C) and normal (at 25 °C) drying techniques. Fourier transform infrared spectroscopy (FT-IR) analysis confirmed that a full conversion of titanium isopropoxide is obtained by the hydrolysis reaction, resulting in formation of TiO₂ particles. X-ray diffraction (XRD) results revealed that both peptisation and drying temperatures influence on preferable orientation growth of anatase and rutile phases on (1 0 5) and (1 0 1) planes, respectively. Moreover, artificial peptisation and cool drying hindered the anatase to rutile phase transformation and crystal growth. The transformation activation energy was calculated in the range 7.5-11 kJ mol^-1 and 11-21 kJ mol^-1 based on peptisation and drying temperatures, respectively. Furthermore, the enthalpy change for crystallisation of prepared titania powders, calculated from differential scanning calorimeter (DSC) analysis, was 10.4 ± 0.3 kJ mol^-1. FE-SEM analysis confirmed that packing and ordering of artificial-peptised and cool-dried powders are much better than in the case of natural-peptised and normal-dried ones, respectively. Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Helenda (BJH) results showed that both artificial peptisation and cool drying are the effectively techniques to enhance specific surface area (SSA) and pore volume of prepared titania powders. The densification process of the powders enhanced, up to 95% of the theoretical value, with decreasing peptisation temperature.