Low temperature solvothermal synthesis of anatase TiO2 single crystals with wholly {100} and {001} faceted surfaces

Abstract

A facile hydrothermal approach for synthesizing anatase TiO₂ single crystals with wholly {100} and {001} facets under a reaction temperature as low as 100 °C is reported. NaBF₄ and NaF are used as the facet control agents instead of HF, which are safer and much easier to use. By adjusting the reaction conditions, the lowest energy {101} facets can be completely eliminated. The anatase TiO₂ with 45% {100} and 55% {001} facets exhibits a considerably higher specific surface photoreactivity than P25. The formation mechanism of the high surface energy facets is explored by XPS and DFT calculations. The results confirm that the reactions of the –OH groups on the surface of anatase TiO₂ that are replaced by F atoms are exothermic and can lower the surface energy of {100} and {001} facets, indicating that anatase TiO₂ with pure high energy facets can be prepared at temperatures as low as 100 °C with the existence of the surface lattice F. It is the first report that the surface lattice F generated in the reaction may stabilize and lead to the disappearance of the lowest surface energy {101} facet under low temperature.