Enhanced dispersion stability and photocatalytic activity of TiO2 particles fluorinated by fluorine gas

The dispersion stability and photocatalytic activity of TiO2 particles were improved by the surface fluorination using fluorine gas (F2) at a pressure less than 50.5 kPa at 25° C. Average particle sizes and zeta potentials of fluorinated TiO2 (F-TiO2) particles in all solvents were approximately 11 times smaller and 1.5 times larger, respectively, than those of untreated TiO2 particles (2.5 × 103 nm and −19 mV). In the photocatalytic activity of TiO2, the UV–vis absorption range of F3-TiO2 with Ti3+ and Ti2+ valences expanded to about 500 nm. Also, the degradation ratio of methylene blue (73%) with F-TiO2 was much higher than that (18%) with untreated TiO2 at 4 h. However, TiOF2 in F4-TiO2 synthesized at 200° C severely affected the dispersion stability and the photocatalysis of TiO2. To optimize the beneficial effects of surface fluorination considering the dispersion stability and photocatalytic activity, it is necessary to control the fluorine content (x), 0 < x < 0.5 in TiO2−xF2x.