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 CH3CH2CH 2OH 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 O 2, 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, OOCCH2NH 2, and carbonyl-containing species of formamide (HCONH2) and formic acid (HCOOH). However, for the OCH2CH2NH 2/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.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films