Photocatalytic properties and photoinduced hydrophilicity of surface-fluorinated TiO₂

Surface-fluorinated TiO₂ was prepared with the help of anhydrous hydrogen fluoride (AHF) via vapor-phase fluorination at 473 K for 2 h and characterized by XRD, SEM, UV-visible diffuse reflectance, Raman, XPS, and ATR-FTIR, respectively. XRD and UV-visible diffuse reflectance show that fluorination does not change the bulk crystal structure and optical absorption of TiO₂ under the above-mentioned preparation condition. However, the photoinduced hydrophilicity, photocatalytic H₂ evolution, and organic contaminant decomposition are greatly improved by the insertion of fluorine. XPS, ATR-FTIR, and Raman measurements of TiO₂ and surface-fluorinated TiO₂ reveal that fluorination remarkably increases the adsorption of polar molecules, including water and some organics, which is mainly attributed to the enhancement of surface acidity, and the formation of the surface hydroxyl radicals, which is beneficial for both photocatalytic oxidation reaction and hydrophilicity. Therefore, as expected, H₂ evolution from water, aldehyde decomposition, and methylene blue degradation increase, and water contact angle decreases, on the surface-fluorinated TiO₂ under UV light irradiation.