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Fourier-transformed infrared spectroscopy has been employed to study the adsorption, thermal reactions and photodegradation of glycolic acid (HOCH 2 COOH) on TiO 2 in a gas–solid system. The intriguing research focus is the reactivity and evolution of the two functional groups. Glycolic acid can exist on TiO 2 at 35 °C in two dissociative adsorption forms, OCH 2 COOH and HOCH 2 COO, which are derived from hydrogen loss of the COH and COOH groups, respectively. Heating the surface to a temperature higher than ∼100 °C causes a largely enhanced carbonyl stretching band at ∼1750 cm −1 , indicative of oxidation of the OCH 2 groups of the surface glycolic acid molecules. This chemical process is supported by the adsorption of glyoxylic acid (HCOCOOH) on TiO 2 . As the surface temperature is further increased to 200 °C or higher, formate (HCOO) and methoxy (CH 3 O) are produced. Their formation is proposed via dioxymethylene (OCH 2 O) intermediate. CO and CO 2 are found to be the final thermal products. Photoirradiation of a TiO 2 surface covered with glycolic acid at ∼325 nm leads to its decomposition, generating CO 2 , CH 3 O, HCOO and carbonate species. O 2 is found to promote the photochemical reactions of glycolic acid on TiO 2 to form CO 2 , HCOO and carbonates. O 2 may play a role hampering recombination of photogenerated electron–hole pairs and participating in the formation of CO 2 and HCOO.

Adsorption, thermal decomposition, and photoreactions of ethylene oxide (EO) on powdered TiO 2 have been studied by Fourier-transformed infrared spectroscopy. Most of the adsorbed EO molecules at the saturated coverage on 35 °C TiO 2 remain intact. As the temperature is increased (≥100 °C), the surface EO molecules dissociate into ethylene glycol-like species (-OCH 2 CH 2 OH or -OCH 2 CH 2 O-) by ring rupture and crotonaldehyde (CH 3 CH=CHCHO) possibly via acetaldehyde from EO isomerization. The ring-opening process is enhanced in the presence of coadsorbed H 2 O molecules. EO with the highly strained three-membered ring is thermally more reactive than 1,4-dioxane on TiO 2 . EO molecules adsorbed on TiO 2 readily undergo photodegradation in O 2 , forming surface H 2 O, CO 2 , HCO 3 , CO 3 , and HCOO. The comparative studies of 16 O 2 and 18 O 2 indicate that both O 2 and lattice oxygen take part in the EO photodecomposition. The reaction pathways involving the two oxygen species are discussed.

Adsorption and reactions of 2-iodoethanol on TiO(2) have been studied by Fourier transform infrared spectroscopy. ICH(2)CH(2)OH possesses two reactive centers of C-I and C-OH. It is found that its decomposition leads to the formation of crotonaldehyde on TiO(2). A reaction sequence of ICH(2)CH(2)OH --ICH(2)CH(2)O- --CH(3)CHO --CH(3)CH=CH-CHO is proposed. Although the decomposition routes of C(2)H(5)OH and C(2)H(5)I, both forming C(2)H(5)O- on TiO(2), suggest that -OCH(2)CH(2)O- may play a role in the crotonaldehyde formation, reaction of HOCH(2)CH(2)OH on TiO(2) shows that this is not the case. Adsorbed H(2)O is formed in the ICH(2)CH(2)OH decomposition on TiO(2); however, it is found that ICH=CH(2), possibly generated by ICH(2)CH(2)OH dehydration, is not important in the crotonaldehyde formation.