Modification of Metal Nanoparticles with TiO₂ and Metal−Support Interaction in Photodeposition

Rh, Pt, and Au metals photodeposited on TiO₂ with an anatase phase (M−TiO₂(p), M: Rh, Pt, Au) were studied using transmission electron microscopy (TEM), scanning transmission electron microscopy, energy dispersive X-ray (EDX) analysis, X-ray absorption fine structure (XAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), and XPS depth profile analysis. The TEM images of Rh−TiO₂(p) and Pt−TiO₂(p) did not clearly show the grain boundary of metal particles, although the Rh and Pt species of Rh−TiO₂(p) and Pt−TiO₂(p) were observed by EDX analysis to show the metal particles 10−20 nm in size. These results suggest that the photodeposited Rh and Pt metal particles have a disorganized structure, which is also supported by extended XAFS spectral analysis. It is speculated that a strong metal−support interaction takes place in the case of Rh and Pt, resulting in the disorganized structure. In the case of Au, however, metal particles with a well-organized and spherical structure were observed, indicating that Au does not strongly interact with TiO₂. The XPS analyses revealed that the surface of metal particles of M−TiO₂(p) received electrons from TiO₂. The XPS depth profile analysis suggests that the metal particles are modified with TiO₂. TiO_2−δ generated by the photoirradiation of TiO₂ can cause the modification and the disorganized structure of Rh and Pt metal particles.