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Formation of a surface complex between organic molecules and TiO₂ is one of the possible strategies for the development of visible light-induced TiO₂ photoactivity. Herein, three ionic liquids (ILs) with the same cation and different anions (1-butylpirydynium chloride/bromide/iodide) have been applied for the surface modification of TiO₂ and to understand the role of anions in visible light-induced activity of ILs-TiO₂ systems. Photocatalytic screening tests (the measurements of phenol photodegradation reaction rate) revealed that anion type affected visible light activity (λ > 420 nm) of TiO₂ obtained by the ILs-assisted solvothermal method. Density functional theory (DFT) calculations demonstrated that interactions between halogen anions and oxygen vacancies (OV) on the surface of the TiO₂ particles could be responsible for the specific wavelength-induced excitation and finally for the observed photoactivity of titania under visible light. Finally, our theoretical calculations have been proven by experiments using monochromatic light (the apparent quantum efficiency was measured) and the properties of obtained samples were characterized using scanning electron microscopy (SEM), X-ray powder diffraction analysis (XRD), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS).