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Abstract: Titanium dioxide (TiO2), co-deposited with Fe and N, is first implanted with Fe by a metal plasma ion implantation (MPII) process and then annealed in N2 atmosphere at a temperature regime of 400–600°C. First-principle calculations show that the (Fe, N) co-deposited TiO2 films produced additional band gap levels at the bottom of the conduction band (CB) and on the top of the valence band (VB). The (Fe, N) co-deposited TiO2 films were effective in both prohibiting electron–hole recombination and generating additional Fe–O and N–Ti–O impurity levels for the TiO2 band gap. The (Fe, N) co-deposited TiO2 has a narrower band gap of 1.97eV than Fe-implanted TiO2 (3.14eV) and N-doped TiO2 (2.16eV). A significant reduction of TiO2 band gap energy from 3.22 to 1.97eV was achieved, which resulted in the extension of photocatalytic activity of TiO2 from UV to Vis regime. The photocatalytic activity and removal rate were approximately two-fold higher than that of the Fe-implanted TiO2 under visible light irradiation. [Copyright &y& Elsevier]

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]

Abstract: Nano-scale TiO2 thin films were synthesized by using sol–gel and spin-coating techniques on glass substrates for photo-catalytic applications. The Ti(IV) butoxide-based TiO2 thin films were optimized for transforming into the high-purity crystalline anatase phase when calcined at 500 °C. To further enhance the photo-catalysis sensitivity of TiO2 thin films for use in visible light environments, a metal plasma ion implantation process was implemented to modify the band gap electron configuration of Ti. Various transition metal atoms such as Ni, Cu, V, and Fe were ionized and accelerated at 20 keV to impinge on the surface of TiO2 substrates at a dosage of 5×1015 ions/cm2. ESCA analysis confirmed the binding energy shift of Ti by 0.8–1.2 eV, which accounted for the increased effective positive charge of Ti, resulting in more effective electron trapping capability and, thus, the electron-hole pair separation. In addition, the absorption spectroscopy demonstrated that optical absorption in the visible light regime occurred in specimens implanted with transition metal ions, likely due to the formation of extra impurity energy levels within the original TiO2 band gap energy structure. Among all tested implant materials, the band gap energy of TiO2 was effectively reduced by Cu and Fe ion implantation by 0.9–1.0 eV, which was sufficient enough to excite valence electrons over the band gap in visible light environments. The feasibility of the metal-doped TiO2 thin films for effective applications under visible light irradiation was further confirmed by using super-hydrophilicity contact-angle measurement. [Copyright &y& Elsevier]