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.