XRD, TEM and Si-29 MAS NMR study of sol-gel ZnO-SiO2 nanocomposites

X-Ray amorphous ZnO nanoparticles homogeneously dispersed in a silica matri x were evidenced in ZnO-SiO2 nanocomposites obtained by a sol-gel method an d heated to 700 degrees C. TEM observations indicated that the particle siz e slowly increases with temperature and zinc oxide content, reaching an upp er limit of 12 nm. Through a comparison of the Si-29 MAS NMR data of the na nocomposites and silica samples, obtained by the same preparation method, i t was possible to observe that reaction occurs between ZnO and silica on he ating, which causes a depolymerization of the host matrix with the formatio n of low condensation groups. This result is discussed in terms of interact ions between nanoparticles and the silica matrix at the nanoparticle/matrix interface. A further increase in temperature (900 degrees C) results in th e formation of the beta-Zn2SiO4 crystalline phase.