Etude des proprietes structurales et optiques des nanocomposites Ag/SiO2

Abstract

In this work, composite silver / silica were studied. In a first step, the Ag+ ions of various compositions (2.5, 5, 7.5 and 10%) were fixed on the silica by ion exchange. In a second step, the samples were annealed in air at temperatures ranging from 100 to 700° C. Several experimental techniques (SEM, XRD, FTIR, UV-Visible) were used to characterize the samples at various stages of development. The X-ray diffraction has identified several phases formed (Ag2Si2O5; Ag2SiO3 ; Ag3Si and Ag) for the respective proportions: 2.5; 5; 7.5 and 10% of Ag+ ions/SiO2. After heat treatment, for a charge of 5%, the X-ray diffraction revealed the formation of silver silicates (Ag4SiO4; Ag6Si2O7; Ag10Si4O13) for temperatures below 500°C and Ag phase to higher temperatures (600 and 700°C). FTIR spectra of the samples Ag/SiO2 present five bands in the region 400 to 2000 cm-1 assigned to the vibration: Si-O-Si, Ag-W, Ag-SO4, Si-O and Si-OH. The spectrum of the sample content of 2.5% Ag+ has well-resolved peaks. The increase of the Ag+ ions load causes an overlap of peaks relating to the groups: Si-O and Si-OH. An FTIR spectrum of displacement toward the low wave numbers was observed after annealing at 200° C. For larger annealing temperatures (300 to 700° C), the spectrum is moved in the opposite direction. This correlates with the formation of large silver nanoparticles. The UV-visible absorption spectrum of nanocomposites Ag/SiO2 has a wide band in the UV region (300 to 370 nm) for the different ion contents Ag+/SiO2. This absorption is attributed to the surface plasmon resonance. Following the heat treatment, a shift of this band to the blue is observed