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 (CH3CH(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 CO2 and acetate. Possible mechanisms for decomposition of lactic acid and poly(lactic acid) on TiO2 are proposed.

In situ Fourier-transform transmission infrared spectroscopy has been employed to investigate the adsorption and photochemistry of 2-ethanolamine (HOCH2CH2NH2) on TiO2 as well as the interaction of CO2 with 2-ethanolamine-modified TiO2 surfaces. Intact HOCH2CH2NH2 and the dissociative form of OCH2CH2NH2 are found to be present on the surface with the saturation coverage of 2-ethanolamine at 35 °C, in comparison to the adsorption of CH3CH2CH2OH and CH3CH2CH2NH2 on TiO2. CO2 reacts with the −NH2 basic centers of the surface 2-ethanolamine molecules, forming carbamate (−NHCOO−) and ammonium (−NH3 +). Bicarbonate (HCO3 −) is also formed due to the presence of residual water. The carbamate species of OCH2CH2NHCOO− has a better thermal stability than HCO3 −. In the presence of O2, as the TiO2 surface with the saturation coverage of 2-ethanolamine is photoirradiated at 325 nm, the infrared studies suggest the formation of isocyanate (NCO), absorbed CO2, OOCCH2NH2, and carbonyl-containing species of formamide (HCONH2) and formic acid (HCOOH). However, for the OCH2CH2NH2/TiO2 surface, H2O, formate (HCOO), carbonates, and a surface species carrying a CN group are found, in addition to NCO. The photoproducts of NCO and absorbed CO2 reveal the C−C bond dissociation pathway of the surface 2-ethanolamine under illumination. Photoreaction mechanisms involving hole capture at different reaction centers and formation of organoperoxide or tetraoxide species have been proposed, on the basis of the products and intermediates identified in the 2-ethanolamine photocatalytic degradation on TiO2 in the presence of 16O2 and 18O2.