Abstract
To investigate the effect of the ionic liquid (IL) chain length on the surface properties and photoactivity of TiO2, a series of TiO2 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 TiO2) was observed for the TiO2 sample obtained in the presence of [TDMIM][Cl] for a IL to TiO2 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–TiO2 semiconductors. In this regard, the direct increase of the photoactivity of IL–TiO2 in comparison to pristine TiO2 was observed. The active species trapping experiments indicated that O2•− is the main active species, created at the surface of the IL–TiO2 material under visible-light illumination, and is responsible for the effective phenol degradation.
Highlights
The development of heterogeneous photocatalysis to degrade organic pollutants in aqueous and gas phases requires visiblelight responsive, stable materials and a basic understanding of these materials [1,2,3,4]
To understand the nature of the visible-light-induced activity (IL:TBOT molar ratio equal to 1:3 and 1:10), the photocatalysts possessing the highest and lowest activity have been selected for further detailed study (SEM, X-ray photoelectron spectroscopy (XPS) and X-ray powder diffraction (XRD))
The results presented in this study revealed that visible-lightresponsive TiO2 microspheres could be successfully obtained by a solvothermal method assisted by ionic liquids, such as 1-methyl-3-tetradecylimidazolium or 1-methyl-3-octadecylimidazolium chlorides
Summary
The development of heterogeneous photocatalysis to degrade organic pollutants in aqueous and gas phases requires visiblelight responsive, stable materials and a basic understanding of these materials [1,2,3,4]. In this comparative study, we have continued the elucidation of the role of the IL (alkyl chain length in the imidazolium cation) as well as the effect of the IL structure on the formation of TiO2 photocatalysts with improved activity towards visible irradiation.
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