The adsorption of water and deuterium oxide on TiO2 surfaces was investigated in the dark as well as under UV(A) irradiation using in situ ATR-FTIR spectroscopy under oxygen and oxygen free conditions.

The simultaneous photocatalytic degradation of formaldehyde and hydrogen evolution on platinized TiO2 have been investigated employing different H2O/D2O mixtures under oxygen-free conditions using quadrupole mass spectrometery (QMS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The main reaction products obtained from the photocatalytic oxidation of 20% formaldehyde were hydrogen and carbon dioxide. The ratio of evolved H2 to CO2 was to 2/1. The HD gas yield was found to be dependent on the solvent and was maximized in a H2O/D2O mixture (20%/80%). The study of the solvent isotope effect on the degradation of formaldehyde indicates that the mineralization rate of formaldehyde (CO2) decreases considerably when the concentration of D2O is increased. On the basis of the ATR-FTIR data, the formaldehyde in D2O is gradually converted to deuterated formic acid during UV irradiation, which was confirmed by different band shifting. An additional FTIR band at 2050 cm–1 assigned to CO was detected and was found to increase during UV irradiation due to the adsorption of molecular CO on Pt/TiO2. The results of these investigations showed that the molecular hydrogen is mainly produced by the reduction of two protons originating from water and formaldehyde. A detailed mechanism for the simultaneous hydrogen production and formaldehyde oxidation in D2O is also presented.

The adsorption and photocatalytic degradation of acetate on TiO2 surfaces was investigated in H2O and D2O by ATR-FTIR and EPR Spectroscopy respectively. These studies were carried out in the dark and under UV(A) illumination to gain additional insights into the adsorption behaviour with the identification of paramagnetic species formed during the oxidation of acetate. Isotopic exchange during the adsorption of D2O on TiO2 surface led to different interactions between the adsorbate and OD groups. At different pH levels, several surface complexes of acetate can be formed such as monodentate, or bidentates. Under UV(A) irradiation of TiO2 aqueous suspensions, the formation of hydroxyl and methoxy radicals evidenced as the corresponding spin-adducts, were found to dominate in alkaline and acidic suspensions respectively. Two possible pathways for the oxidation of acetate have been suggested at different pH levels in solution in terms of the source of the spin adduct formed.These proposed pathways were found to be in good agreement with ATR-FTIR and EPR results.

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