Excitation Wavelength Dependence of Photocatalyzed Oxidation of Methanol on TiO2(110)

Post-irradiation temperature-programmed desorption (TPD) has been used to study the photocatalyzed oxidation of methanol on TiO₂(110) surface under the irradiation of 360, 380 and 400 nm light. The photocatalytic process initiated by ultraviolet light of different wavelength are similar. Methanol has been photocatalytically converted into formaldehyde, and the released hydrogen atoms transfer to the neighboring twofold coordinated oxygen to form bridging hydroxyls. The reaction rate, however, is strongly wavelength dependent. The reaction rate under 360 nm light irradiation is 4.8 times of that in the case of 400 nm exposure, consistent with a previous femtosecond time-resolved absorption measurement on TiO₂ which shows the faster charge carrier recombination in the near-band-gap than the over-band-gap excitation. So far, the underlying factors which govern the excitation wavelength dependence of photocatalytic activity of TiO₂ and other photocatalysts remain unclear, and future studies are needed to address this important issue.