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Abstract: Photocatalyst titanium dioxide (TiO2) thin films were prepared using sol–gel process. To improve the photosensitivity of TiO2 at visible light, transition metal of Fe was implanted into TiO2 matrix at 20keV using the metal plasma ion implantation process. The primary phase of the Fe-implanted TiO2 films is anatase, but X-ray diffraction revealed a slight shift of diffraction peaks toward higher angles due to the substitutional doping of iron. The additional band gap energy levels were created due to the formation of the impurity levels (Fe–O) verified by X-ray photoelectron spectroscopy, which resulted in a shift of the absorption edge toward a longer wavelength in the absorption spectra. The optical band gap energy of TiO2 films was reduced from 3.22 to 2.87eV with an increase of Fe ion dosages from 0 to 1×1016 ions/cm2. The band gap was determined by the Tauc plots. The photocatalysis efficiency of Fe-implanted TiO2 was assessed using the degradation of methylene blue under ultraviolet and visible light irradiation. The calculated density of states for substitutional Fe-implanted TiO2 was investigated using the first-principle calculations based on the density functional theory. A combined experimental and theoretical Fe-implanted TiO2 film was formed, consistent with the experimentally observed photocatalysis efficiency of Fe-implanted TiO2 in the visible region. [Copyright &y& Elsevier]