Preparation of porous rutile titania from ilmenite by mechanical activation and subsequent sulfuric acid leaching

Synthesis of porous titania via mechanical activation of natural ilmenite and subsequent simultaneous dissolution and hydrolysis in dilute solutions of sulfuric acid was investigated by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), N2 adsorption/desorption measurements, energy-dispersive X-ray spectrometry (EDX) and thermogravimetric analysis (TG). This is a novel template-free approach for synthesis of microporous, mesoporous and micro–mesoporous TiO2 materials. Effects of sulfuric acid concentration and calcination temperature on physicochemical properties of the TiO2 materials were examined systematically. The results show that both the factors considerably affected the porosity of the materials. In a 15% acid solution a microporous TiO2 hydrolysate with BET surface area 109.3 m2/g was prepared. With a 10% H2SO4, we obtained a more pure micro/mesopore TiO2 hydrolysate with BET area of 257.6 m2/g. Calcining the hydrolysate at ⩾500 °C led to the formation of a mesopore TiO2. The mesoporous TiO2 generated at 600 °C still has a BET area of 92.1 m2/g. The high thermal stability is probably related to the presence of H2SO4 in the channel walls of hydrolysate. The XRD analysis indicated all the TiO2 materials prepared in this study being rutile. The mechanism for formation of the porous rutile TiO2 is mainly via in situ hydrolysis and precipitation of the dissolved titanium on the un-reacted ilmenite surface, where H2SO4 may play a very important role.