Synthesis of micro-sized hierarchical TiO2 particles of nano-scale effectiveness and their photocatalytic activities at various surface hydroxyl concentrations

The 3-dimensional hierarchical TiO₂ particles of micro-sized diameter were synthesized through modified sol–gel process with polyethylene glycol (PEG) as a structure-controlling agent. The anatase crystal structure was obtained after calcination at 450 °C. The size and specific surface area of particles were 1.0–1.8 μm and 96.85 m² g⁻¹, respectively. The specific surface area of the TiO₂ particles corresponded to that of the spherical nanoparticles with average size of 15.9 nm. Although the size of synthesized TiO₂ was micro-scale, they had the specific surface area similar to that of nano-scale particles due to the effect of PEG on the formation of particles. Subsequently, the surface modification with various concentration of ammonia solution was carried out for the preparation of hydroxyl-rich TiO₂ particles at surfaces. As the concentration of ammonia solution was increased, the amount of chemically adsorbed hydroxyl groups on the TiO₂ surface was increased. As an application of prepared TiO₂ for water treatment, their catalytic performances for the degradation of methylene blue (MB) were examined by using UV–Vis spectrophotometer with the assistance of UV lamp. After hydroxylation treatment, the micro-sized TiO₂ particles showed the higher performance of MB degradation than that of nano-sized P25 particles because of their large specific surface area and hydroxyl-rich surface.