Pivotal role of fluorine in enhanced photocatalytic activity of anatase TiO2 nanosheets with dominant (0 0 1) facets for the photocatalytic degradation of acetone in air

Surface-fluorinated anatase TiO2 nanosheets with dominant {0 0 1} facets were fabricated by a simple hydrothermal route in a Ti(OC4H9)4-HF-H2O mixed solution. The atomic ratios of fluorine to titanium (RF) exhibit an obvious influence on the structures and photocatalytic activity of TiO2 samples. In the presence of HF, TiO2 nanosheets can be easily obtained. With increasing RF, the relative anatase crystallinity, average crystallite size, pore size and percentage of exposed {0 0 1} facets increase, contrarily, BET specific surface areas decrease. All fluorinated TiO2 nanosheets exhibit much higher photocatalytic activity than Degussa P-25 TiO2 (P25) and pure TiO2 nanoparticles prepared in pure water due to the synergistic effect of surface fluorination and exposed {0 0 1} facets on the photoactivity of TiO2. Especially, at RF = 1, the fluorinated TiO2 nanosheet exhibits the highest photocatalytic activity, and its photoactivity exceeds that of P25 by a factor of more than nine times.