In Situ ATR-FTIR Investigation of the Effects of H2O and D2O Adsorption on the TiO2 Surface

Abstract

We have investigated the behavior of H2O and D2O adsorption on TiO2 surfaces in the dark and under UV irradiation using in situ ATR-FTIR spectroscopy. The influence of an electron scavenger (oxygen) and a hole scavenger (ethanol) on the hydroxyl group and/or hydration water behavior on the TiO2 surface were also investigated. Adsorption of H2O–D2O mixtures revealed an isotopic exchange reaction occurring in the dark onto the surface of the TiO2 material. Under UV(A) irradiation, the amount quanitity of both OH and OD groups was found to be increased by the presence of molecular oxygen. On the other hand, the ATR-FTIR study of the ethanol adsorption in H2O and D2O reveals revealed a stronger adsorption ability ofcapacity for ethanol compared to both H2O and D2O resulting in molecular and dissociative adsorption of ethanol on the TiO2 surface. When the system was subsequently illuminated with UV(A) light, the surface becomes enriched with adsorbed water. Different possible mechanisms and hypotheses are discussed in terms of the effect of UV irradiation on the TiO2 particle network for the photocatalytic reaction and photoinduced hydrophilicity.