Rapid synthesis of a TiO2 hollow microsphere assembly from hollow nanoparticles with enhanced photocatalytic activity

A novel hierarchical anatase TiO2 hollow microsphere (TiO2-HMS) assembly synthesised from TiO2 hollow nanoparticles (TiO2-HNP), denoted TiO2-HMS-HNP, was rapidly fabricated by a simple hydrothermal route in a Ti(SO4)2–NH4F–H2O2 mixed solution at 180 °C for only 3 h. The influence of NH4F and H2O2 on the formation of TiO2-HMS-HNP was studied. A novel mechanism for the formation of TiO2-HMS-HNP based on a H2O2-assisted fluoride-induced self-transformation (FIST) process is proposed. The prepared TiO2-HMS-HNP showed much higher photocatalytic activity than TiO2-HMS, when the activity was evaluated both by the photocatalytic degradation rate of brilliant red X-3B (an anionic azo dye) and by the rate of formation of photo-induced hydroxyl radicals (˙OH) under UV irradiation.