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

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. Copyright © 2017 Dalian Institute of Chemical Physics, the Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.