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. TiO2−δ generated by the photoirradiation of TiO2 can cause the modification and the disorganized structure of Rh and Pt metal particles.