Infrared Spectroscopic Study of Adsorption and Reactions of Glyoxylic Acid on TiO2

Abstract

Fourier transform infrared spectroscopy has been employed to investigate the adsorption, thermal reactions, and photodegradation of glyoxylic acid on TiO2 in a gas−solid system. Glyoxylic acid may exist on TiO2 at 35 °C with several dissociative adsorption forms, through the interaction of the carboxyl group or the diol group derived from carbonyl transformation. CO, CO2, HCOO (formate), and CH3O (methoxy) are found to be the thermal reaction products. A C−C bond scission pathway is proposed for the formation of CH3O via −OCH2O− (dioxymethylene), which can undergo self oxidation−reduction. However, another possible route producing oxalic acid or oxalate is not important. Moreover, O2 has no effect on the decomposition of the surface glyoxylic acid and on the formation temperature of the thermal reaction products. In the photochemistry of glyoxylic acid on TiO2 irradiated at 400 nm, it produces CO2, carbonate, and HCOO. O2 can enhance the formation of CO2 and carbonate species. The 18O2 isotopic study shows that the CO2 and carbonates formed in the initial photoirradiation stage (≤10 min) may only contain a small amount of 18O. The role dioxygen may play in the initial photodecomposition of glyoxylic acid on TiO2 is to capture the photogenerated electrons, increasing the lifetime of holes and thus the photooxidation efficiency, but hardly directly participating in the product formation.