FTIR study of adsorption and photoreactions of acetic acid on TiO2

Fourier-transformed infrared spectroscopy has been employed to study the adsorption and photoreactions of acetic acid on powdered TiO2. Molecular acetic acid and acetate groups are present on TiO2 following acetic acid adsorption at 35 degreesC. Acetic acid is adsorbed via hydrogen bonding or Lewis acid-base interaction and is removed at 170 degreesC, leaving acetate on the surface. The adsorbed acetate groups adopt a bidentate coordination. CO2(g) is detected as a photoproduct in the UV irradiation of surface acetate. In the presence of water, some surface acetate is converted into acetic acid, and, in this case, both CO2(g) and CH4(g) are observed in the photoillumination. However, effect of water on the reaction rate for CO2(g) and CH4(g) formation is not significant. O-2 can increase the photodecomposition rate of acetic acid on TiO2, and in addition to CH4(g) and CO2(g), oxygenated compounds such as CH3OH(g), CH2O(g) and HCOOCH3(g) are detected. It is likely that these species are generated due to O-2(-), produced from photoelectrons and O-2, attacking adsorbed acetic acid molecules instead of attacking acetate groups.