Surface Defect-Controlled Growth and High Photocatalytic H₂ Production Efficiency of Anatase TiO₂ Nanosheets

Facet engineering of anatase TiO₂ by controlling the {001} exposure ratio has been the focus of numerous investigations to optimize photocatalytic activity. In particular, an introduction of fluoride ions during the crystal growth has been demonstrated to be very effective and decisive in realizing the facet exposure of the crystals. However, a key role of fluoride ions in stabilizing {001} exposure and improving subsequent photocatalytic activity of anatase TiO₂ remains unclear up to date. Herein, a controlled thickness of anatase TiO₂ nanosheets has been realized by introducing different amounts of ethanol into a HF acid-assisted hydrothermal reaction. The thinnest nanosheets with a thickness of ∼2.9 nm were evaluated to have the highest H₂ production rate of 41.04 mmol·h^-1·g^-1 under ultraviolet light irradiation, and the corresponding quantum efficiency was determined to be 41.6% (λ = 365 nm). Moreover, it is proved for the first time that fluoride ions are bonded with Ti vacancies on {001} facets, and such defects are crucial for stabilizing the ultrathin nanosheets and improving their electron-hole separation, therefore leading to a highly efficient photocatalytic activity. The findings offer an opportunity to engineer facets and functionality of anatase TiO₂ by controlling surface defects.