Adsorption of Thiol-Protected Gold Nanoparticles on TiO2 and Their Behavior under UV Light Irradiation

A combination of in situ attenuated total reflection infrared (ATR-IR) spectroscopy, UV−vis spectroscopy and transmission electron microscopy was used to study the adsorption of thiol-protected gold nanoparticles on TiO 2 films and the behavior of the resulting composite films upon UV irradiation. The gold nanoparticles were covered by charged thiols N -acetyl- l -cysteine and l -glutathione and had a mean core diameter of about 1 nm. The TiO 2 film was prepared by deposition of a slurry of TiO 2 nanoparticles with a particles size of 21 nm. The combination of the two spectroscopic techniques showed that the adsorption of the gold nanoparticles onto the TiO 2 films is significantly limited by intrafilm diffusion. Upon illumination the IR spectra revealed the removal of the adsorbed thiolates and the appearance of sulfates. These species were also observed when N -acetyl- l -cysteine adsorbed on TiO 2 was illuminated, i.e., in the absence of gold. In the latter case oxalate was observed in large quantity on the TiO 2 surface, in contrast to the illumination of the N -acetyl- l -cysteine-protected gold particles. This indicates a different pathway for the decomposition of the adsorbed thiol when adsorbed on the gold or directly on the TiO 2 surface. In situ UV−vis spectroscopy also shows the formation of larger particles upon illumination, which is confirmed by transmission electron microscopy.