Sol-gel hot injection synthesis of ZnO nanoparticles into a porous silica matrix and reaction mechanism

Abstract

Despite the enormous interest in the properties and applications of porous silica matrix, only a few attempts have been reported to deposit metal and metal oxide nanoparticles (NPs) inside the porous silica matrix. We report a simple approach (i.e. sol-gel hot injection) for insitu synthesis of ZnO NPs inside a porous silica matrix. Control of the Zn:Si molar ratio, reaction temperature, pH value, and annealing temperature permits formation of ZnO NPs (≤10nm) inside a porous silica particles, without additives or organic solvents. Results revealed that a solid state reaction inside the ZnO/SiO2 nanocomposites occurs with increasing the annealing temperature. The reaction of ZnO NPs with SiO2 matrix was insignificant up to approximately 500°C. However, ZnO NPs react strongly with the silica matrix when the nanocomposites are annealed at temperatures above 700°C. Extensive annealing of the ZnO/SiO2 nanocomposite at 900°C yields 3D structures made of 500nm rod-like, 5–7μm tube-like and 3–5μm needle-like Zn2SiO4 crystals. A possible mechanism for forming ZnO NPs inside porous silica matrix and phase transformation of the ZnO/SiO2 nanocomposites into 3D architectures of Zn2SiO4 are carefully discussed.