Fabrication and photoactivity of ionic liquid-TiO 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, a series of TiO 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) was observed for the TiO sample obtained in the presence of [TDMIM][Cl] for a IL to TiO 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 semiconductors. In this regard, the direct increase of the photoactivity of IL-TiO in comparison to pristine TiO was observed. The active species trapping experiments indicated that O is the main active species, created at the surface of the IL-TiO material under visible-light illumination, and is responsible for the effective phenol degradation.