Fabrication and photoactivity of ionic liquid–TiO(2) structures for efficient visible-light-induced photocatalytic decomposition of organic pollutants in aqueous phase

To investigate the effect of the ionic liquid (IL) chain length on the surface properties and photoactivity of TiO(2), a series of TiO(2) microspheres have been synthesized via a solvothermal method assisted by 1-methyl-3-octadecylimidazolium chloride ([ODMIM][Cl]) and 1-methyl-3-tetradecylimidazolium chloride ([TDMIM][Cl]). All as-prepared samples were characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission microscopy (STEM) and the Brunauer–Emmett–Teller (BET) surface area method, whereas the photocatalytic activity was evaluated by the degradation of phenol in aqueous solution under visible light irradiation (λ > 420 nm). The highest photoefficiency (four times higher than pristine TiO(2)) was observed for the TiO(2) sample obtained in the presence of [TDMIM][Cl] for a IL to TiO(2) precursor molar ratio of 1:3. It was revealed that interactions between the ions of the ionic liquid and the surface of the growing titanium dioxide spheres results in a red-shift of absorption edge for the IL–TiO(2) semiconductors. In this regard, the direct increase of the photoactivity of IL–TiO(2) in comparison to pristine TiO(2) was observed. The active species trapping experiments indicated that O(2)(•−) is the main active species, created at the surface of the IL–TiO(2) material under visible-light illumination, and is responsible for the effective phenol degradation.