Because of the tremendous structural diversity of ionic liquids (ILs), simple transfer of observations performed for one IL used for IL-TiO 2 preparation on different samples is not possible. Therefore, four ionic liquids, all containing distinct nitrogen-bearing organic cations (pyridinium, pyrrolidinium, ammonium, imidazolium), were used for the first time for the preparation of IL-TiO 2 composites. The role of the individual IL cation in the synthesis of TiO 2 microspheres, as well as the effect of the IL structure on the mechanism of the visible-light (Vis)-induced photoactivity of IL-TiO 2 was presented and discussed in regard to structure, morphology, absorption properties, elemental composition, and reactive species involved in the photocatalytic reaction of phenol degradation. The successful modification of the TiO 2 with organic IL species including possible interactions between IL and TiO 2 surface, as well as the TiO 2 matrix (doping with N), were confirmed. The sample that exhibited the highest photoactivity under Vis irradiation (58%) was TiO 2 prepared in a presence of 1-butylpyridinium chloride with a IL:precursor molar ratio of 1:3. For this sample, the highest partial decomposition of cationic species of IL was observed resulting in interaction of N atoms with deeper sites of TiO 2 (Ti-N x ) as well as the highest surface defects in a form of Ti 3+ . The superoxide radical species O 2• − were found to be main active species responsible for high efficiency of degradation under Vis irradiation.

The effect of the ionic liquid's (IL) anion type ([BMIM][X], where BMIM=1‐butyl‐3‐methylimidazolium and X=[Br], [PF6], or octylsulfonate [OctSO4]) and IL content on the morphology, surface properties, and photoactivity of TiO2 obtained by the solvothermal method has been systematically investigated. Our results revealed that the presence of [Br] and [OctSO4] anions favor the formation of anatase phase, whereas the presence of [PF6] causes formation of anatase and Ti(OH)PO4 phase mixtures. The highest photocatalytic activity under visible radiation (approximately four times higher than pristine TiO2) was observed for the TiO2 sample grown in the presence of 1‐butyl‐3‐methylimidazolium bromide for ionic liquid to TiO2 precursor molar ratio 1:2. Visible‐light‐induced phenol degradation was found to be realized mainly by oxygen radical anions, whereas the contributions of the other processes involving reactions with trapped electrons, holes, and hydroxyl radical, are limited in the overall reaction mechanism. Quantum chemical calculations on a model of anatase vacancy suggest that the charge transfer between the bromide anion and molecular oxygen interacting with the vacancy is a source of photoactivity induced by visible photons.

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