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 H-2 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, H-2 evolution from water, aldehyde decomposition, and methylene blue degradation increase, and water contact angle decreases, on the surface-fluorinated TiO2 under UV light irradiation.