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TiO2 has attracted considerable attention because it is known to have strong activity as a photocatalyst. TiO2 films with thicknesses of about 500 nm were deposited on glass slide substrates, sputtering from facing targets. Nitrogen was introduced at gas flow rate of 0 and 5 ccm. Subsequently, the sputtering pressure was fixed at 0.8 Pa introducing mixed gas of Ar and O2. Ar/O2 ratios (GR) were 8:2, 7:3 and 6:4. The decomposition of gaseous methyl alcohol was performed to investigate the dependence of the photocatalytic reactions on the crystallographic structures and optical properties of films. In all TiO2 films, the A(002), A(211) and A(112) diffraction peaks were observed from the x-ray patterns regardless of nitrogen doping and GR, while the A(101) diffraction peaks were slightly observed, where A indicates anatase TiO2. The changes in the optical transmittance spectra of the TiO2 films were very small with varying GR and doping nitrogen. The optical transmittance spectra of films showed changes, with characteristic waveforms that depend on photon interference due to film transparency. The transmittances of all the TiO2 films were constant at 70-90 % for wavelengths in the range of 900 nm to 380 nm. At wavelength less than 380 nm, the transmittance abruptly decreased to zero. The as-deposited films successfully photocatalyzed the decomposition reaction of CH3OH to CO2 and H2O, according to the infrared transmittance spectra. The maximum values of the decomposition rates were found at GR values of 7:3 for 0 ccm nitrogen doping, and 6:4 and 8:2 for 5 ccm nitrogen doping. For films deposited at GR value of 6:4 and 5 ccm nitrogen doping, the CO2 formation rates were about 2 times higher than those prepared with 0 ccm nitrogen doping for a solar irradiation time of 180 min. In conclusion, TiO2 films deposited in this study showed the significant dependence of gas ratio and nitrogen doping on decomposition of gaseous methyl alcoho1. |