Porous TiO₂ with a controllable bimodal pore size distribution from natural ilmenite

Ilmenite (FeTiO₃) is an inexpensive abundant natural mineral and it would be a perfect precursor for the production of porous TiO₂ if a suitable synthesis method was developed. A new method combining a series of processing steps of ball milling, high-temperature annealing, selective chemical leaching and final calcining in air is proposed in this paper. The resulting TiO₂ is a porous material with a bimodal pore structure. The pore size distribution has two clear maxima corresponding to small mesopores (2-30 nm) and large meso- and macropores (centered at around 50-80 nm). It was found that the duration of the annealing step could alter the contribution of each type of pores. A short annealing time (0.5 h) lead to the preferential formation of pores within 2-30 nm while pores centered at 50-80 nm dominated the pore size distribution after a relatively long annealing (1.5 h). The obtained porous rutile TiO₂ shows a better photocatalytic activity than that of a commercial rutile TiO₂ powder.