Photocatalytic Oxidation of Acetone Over High Thermally Stable TiO₂ Nanosheets With Exposed (001) Facets

Anatase TiO₂ (A-TiO₂) usually exhibits superior photocatalytic activity than rutile TiO₂ (R-TiO₂). However, the phase transformation from A-TiO₂ to R-TiO₂ will inevitably happens when the calcination temperature is up to 600°C, which hampers the practical applications of TiO₂ photocatalysis in hyperthermal situations. In this paper, high energy faceted TiO₂ nanosheets (TiO₂-NSs) with super thermal stability was prepared by calcination of TiOF₂ cubes. With increase in the calcination temperature from 300 to 600°C, TiOF₂ transforms into TiO₂ hollow nanoboxes (TiO₂-HNBs) assembly from TiO₂-NSs via Ostwald Rippening process. Almost all of the TiO₂-HNBs are disassembled into discrete TiO₂-NSs when calcination temperature is higher than 700°C. Phase transformation from A-TiO₂ to R-TiO₂ begins at 1000°C. Only when the calcination temperature is higher than 1200°C can all the TiO₂-NSs transforms into R-TiO₂. The 500°C-calcined sample (T500) exhibits the highest photoreactivity toward acetone oxidation possibly because of the production of high energy TiO₂-NSs with exposed high energy (001) facets and the surface adsorbed fluorine. Surface oxygen vacancy, due to the heat-induced removal of surface adsorbed fluoride ions, is responsible for the high thermal stability of TiO₂-NSs which are prepared by calcination of TiOF₂ cubes.