Uniform-sized amorphous hydrous titania particles (HTPs) with nonporous or porous surface were prepared and subjected to hot-water or hydrothermal treatment to induce crystallisation of the titania phase for preparing porous titania particles with high specific surface area (SSA) and outer diameter in a micron order. Porous HTPs were crystallised under milder treatment conditions than those required to crystallise nonporous spherical HTPs. This difference was attributed to the difference in the polycondensation states of hydrous titania. The SSA of the porous titania particles crystallised by hot-water treatment at 80°C for 24 h was 216 m 2 g −1 , despite their micron-order particle size. This simple method can synthesise highly functional titania particles at low temperatures and is a generalpurpose method for preparing porous particles for use as adsorbents, catalysts and catalyst supports.

The synthesis of porous titania microparticles with high specific surface area and sufficient photocatalytic activity is an important but challenging task. To this aim, micron-sized porous titania particles exhibiting photocatalytic activity comparable to that of titania nanoparticles were prepared in this study via hydrothermal treatment of porous hydrous titania particles. First, amorphous porous hydrous titania particles were prepared via hydrolysis of titanium alkoxide followed by partial dissolution of the particle surface by soaking in ethanol. Then, porous hydrous titania particles dried at 75 °C (Dry particles) and without drying (Wet particles) were respectively crystallized using hot water (<100 °C) or via hydrothermal treatment. Both types of particles were crystallized to anatase having a mesoporous structure and a preserved spherical outer shape under hydrothermal treatment. The mesoporous structure was controllable by tuning the treatment temperature, especially in the case of Wet particles. The porous titania particles prepared from Wet particles showed better photodegradation activity toward Evans blue under UV irradiation than those prepared from Dry particles, which is attributable to the distortion of titania crystallites prepared from Wet particles. In fact, despite their micronorder size, the photodegradation ability of Wet particles hydrothermally treated at 160 °C for 24 h was comparable to that of AEROXIDE µ TiO 2 P25.