In situ Fourier transform infrared spectroscopy has been employed to investigate the adsorption and thermal decomposition of lactic acid and poly(lactic acid) on TiO2 with and without O2. Lactic acid dissociates primarily by deprotonation of COOH to form lactate (CH 3CH(OH)COO) on TiO2 and by O-H (alcohol's functional group) bond scission to form 2-oxy-propionic acid (CH3CH(O)COOH). As the surface temperature is raised higher than ∼250 °C in a vacuum, propionate is formed with minor acetate. In contrast, only acetate is formed with simultaneous CO2 evolution in the lactic acid decomposition in the presence of O2. No other products, such as acrylate from dehydration or pyruvate from oxidation of the OH group, are found. Poly(lactic acid) can dissociate by breaking the ester linkage, forming carboxylate species, on TiO2 at 30 °C. Poly(lactic acid) has the same high-temperature reaction products as those of lactic acid on TiO2. Besides, poly(lactic acid) on TiO2 irradiated at ∼320 nm in the presence of O2 is subjected to photodecomposition, generating CO 2 and acetate. Possible mechanisms for decomposition of lactic acid and poly(lactic acid) on TiO2 are proposed.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films