Structural and optical properties of Ag/Si02 nanocomposites

Abstract

In this work, Ag/SiO2 composites were studied for various silver contents (2.5, 5, 7.5 and10% wt). In a first step, Ag+ ions were adsorbed on silica by ionic exchange. In a secondstep, the samples were annealedin air at several temperatures (100-700° C). Several experimentaltechniques (SEM, XRD, FTIR, UV-Visible) were used to characterizethe samples. After ionic exchange, XRD revealed the presence of several silicate phases (Ag2Si2O5; Ag2SiO3 andAg3Si). After heat treatment, for a 5% wt Ag content, silver silicates (Ag4SiO4; Ag6Si2O7; Ag10Si4O13) and Ag phase were identified by XRD. All of the observed phases were nanosized. FTIR spectraof Ag/SiO2presentfivebandsin the region400 to 2000cm-1assigned to thevibration of Si-O-Si, Ag-O, Ag-SO4, Si-O andSi-OH groups.The increaseofthesilvercontentcausesan overlap ofSi-O andSi-OH peaks. A shift of the FTIRspectrumtoward the lowwave numberswas observedafter annealing at200° C.For highertemperatures(300-700° C), thespectrumwas moved inthe opposite direction.This correlates withthe formation of silver nanoparticles. TheUV-visibleabsorptionspectrumof Ag/SiO2nanocomposites presentes awideband situated between 300 to370 nm. This absorptionwas attributed to thesurface plasmonresonance of Agn clusters. After heat treatment, a shiftof this bandtotheblueisobserved, which correlates with the formation of larger silver nanoparticles.