Morphology control in anatase TiO₂ mesocrystals through hydrofluoride incorporation for photocatalytic application

Mesocrystal is a promising material for improving photocatalytic activity because of its large specific surface area and almost single crystalline structure. In this work, anatase TiO₂ mesocrystals were synthesized via a simple hydrothermal process and the morphology and consequent photocatalytic property was controlled through hydrofluoride (HF) addition. The morphology of TiO₂ was significantly varied with the amount of HF addition. The pure TiO₂ was elliptical mesocrystal, having bipyramidal sub units with high portion of {101} facets, arraying in the [001] direction. Similar mesocrystal morphologies were obtained, but the sub unit size decreased as HF content increased to 0.01 wt%, and the shape of the sub unit then changed to nanosheet with the introduction of further HF (1-2 wt%). The 0.01 wt% sample exhibited superior photocatalytic activity over the pure sample, decomposing ∼70% and ∼80% methylene blue in 1 h for the pure sample and 0.01 wt% sample, respectively, resulting from enlarged specific surface area and fluorinated surface. The photocatalytic activity reduced to ∼20% for the 1-2 wt% particles due to the decrease in surface area and formation of the TiOF₂ phase. The present work suggests that the morphology and photocatalytic activity of TiO₂ mesocrystal are facilely modified through HF introduction.