Distinguishing the nature of silver incorporated in sol-gel silica.

Silica glass doped with silver was synthesized using the sol-gel method. The formation of the silica network and the purity of samples were confirmed by Fourier transform infrared spectroscopy. The nature of silver as a function of annealing temperature was investigated using X-ray diffraction (XRD), UV–Vis spectrophotometry, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) techniques. The obtained results from XRD and UV–Vis absorption showed similar information which both confirmed the formation of Ag nanoparticles (NPs) in the samples annealed at high temperature, but revealed nothing about the nature of Ag in the as-prepared samples and those annealed at low temperature. The images and diffraction patterns from HRTEM showed the interesting result that even for the as-prepared sample some of the Ag ions were converted to Ag NPs. This result was further confirmed by XPS data. Moreover, the HRTEM images showed that an increase in the annealing temperature increases the size of the Ag NPs, although the shape of the NPs remains almost unchanged. The quantitative information extracted from XPS results revealed that the ratio of Ag NPs to Ag ions increases with increasing annealing temperature. [ABSTRACT FROM AUTHOR]