Interfacial nature of Ag nanoparticles supported on TiO2 photocatalysts

Silver nanoparticles supported on anatase TiO2 nanoparticles have been prepared by deposition–precipitation, and characterized by X-ray photoelectron spectroscopy, including scanning electron microscopy, X-ray diffraction crystallography, Raman, and UV–visible absorption spectroscopy. The Ag 3d peak and the X-ray diffraction patterns show characteristics of purely metallic Ag, with no indication of Ag oxide species. Depth-profiling X-ray photoelectron spectroscopy with Ar+ ion beam sputtering show a significant change in Ti 2p, and an asymmetric broadening of Ag 3d to a higher binding energy side. A decrease in major Ti 2p 3/2 at 459.2 eV and a significant increase in lower binding energy peak are due to change in oxidation state of Ti from +4 to +3/+2. A broadening of Ag 3d peak with sputtering time is tentatively assigned to a final state quantum size effect. Upon annealing the deposition–precipitation sample, no significant change in Ag 3d peak is observed, while Ti 2p and O 1s XPS intensities are reduced, plausibly due to change in analyzed surface area for TiO2. The photocatalytic activity for the photodegradation of methyl orange is dramatically reduced upon high Ag-loading, compared to bare TiO2. The X-ray photoelectron spectroscopy of Ag on TiO2 prepared by an electrochemical deposition reveals that Ag is also metallic, with no evidence of an oxide form. Upon annealing the electrodeposited sample, the Ag 3d peak shifts by +0.3 eV, while the Ti 2p and O 1s show no critical change in intensity and peak position.