Preparation of F-Doped TiO2 Photocatalysts by Gas–Liquid Plasma at Atmospheric Pressure

F-Doped TiO 2 was successfully fabricated using gas–liquid cold plasma with different fluorine sources, including NaF, NaF combined with [C 4 MIM]HSO 4 , and [C 4 MIM]BF 4 . The samples were characterized by XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), and BET (N 2 adsorption–desorption isotherms). Photocatalytic activity of the samples was tested by degradation of methylene blue (MB) dye under simulated sunlight. The results show that doping with different fluorine sources was beneficial to form interstitial F-doped TiO 2 , and ionic liquids used in our work were most favorable to the formation of interstitial F-doped TiO 2 . Calcination of the 0.6-F–[C 4 MIM]BF 4 –TiO 2 sample at 500 °C shows that interstitial F-doped TiO 2 has an excellent thermal stability, a suitable mesoporous structure, higher specific surface area (60.5 m 2  g −1 ) and the best photocatalytic activity. MB degradation was about 98% under the stimulated sunlight for 30 min, and its apparent rate constant was 42 times higher than photolysis and was about 2.9 times as that prepared without addition of ionic liquid. Furthermore, the stability of ionic liquids in the gas–liquid plasma was also investigated and discussed with the assistance of Fourier transform infrared (FTIR) spectroscopy.