Highly photoreactive TiO2 hollow microspheres with super thermal stability for acetone oxidation

Abstract

TiO2 hollow microspheres (TiO2-HMSs) have attracted much attention because of their high photoreactivity, low density, and good permeability. However, anatase TiO2-HMSs have poor thermal stability. In this study, surface-fluorinated TiO2-HMSs were assembled from hollow nanoparticles by the hydrothermal reaction of the mixed Ti(SO4)2–NH4HF–H2O2 solution at 180 °C. The effect of the calcination temperature on the structure and photoreactivity of the TiO2-HMSs was systematically investigated, which was evaluated by photocatalytic oxidation of acetone in air under ultraviolet irradiation. We found that after calcination at 300 °C, the photoreactivity of the TiO2-HMSs decreases from 1.39 × 10−3 min−1 (TiO2-HMS precursor) to 0.82 × 10−3 min−1 because of removal of surface-adsorbed fluoride ions. With increasing calcination temperature from 300 to 900 °C, the building blocks of the TiO2-HMSs evolve from truncated bipyramidal shaped hollow nanoparticles to round solid nanoparticles, and the photoreactivity of the TiO2-HMSs steady increases from 0.82 × 10−3 to 2.09 × 10−3 min−1 because of enhanced crystallization. Further increasing the calcination temperature to 1000 and 1100 °C results in a decrease of the photoreactivity, which is ascribed to a sharp decrease of the Brunauer–Emmett–Teller surface area and the beginning of the anatase–rutile phase transformation at 1100 °C. The effect of surface-adsorbed fluoride ions on the thermal stability of the TiO2-HMSs is also discussed.