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

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