IN-SITU EXAFS STUDY OF THE PHOTOCATALYTIC REDUCTION AND DEPOSITION OF GOLD ON COLLOIDAL TITANIA

The photocatalytic reduction of gold on a colloidal TiO2 sample in the presence of i-PrOH has been studied by in situ EXAFS. This colloidal sample shows a quantum size effect in its band gap UV-vis absorption and a photocatalytic activity for the formation of Ti3+ species. An experimental setup has been used that consists of a photochemical reactor connected to a peristaltic pump and an EXAFS transmission cell specially designed for liquid samples. The results show that it is possible to follow the two-step mechanism of the photoreduction of noble metals on titania, i.e, the nucleation and the growth of the metallic crystallites. At the same time, a surprisingly low intensity of the threshold feature at the Au L(III) edge has been found for low irradiation times, when small gold particles are formed. This effect has been interpreted as a result of a negative charge injection into the metal particles which is favored by the presence of the alcohol acting as a hole trap. For comparison, an in situ XPS analysis has been carried out to follow the photoreduction of gold in a Au3+-TiO2 material in the presence of i-PrOH at the gas-solid interface.