ZnO-SiO2 based nanocomposites prepared by a modified sol-gel method

This paper presents a study on nanocomposites formation in ZnO-SiO2 systems with different ZnO:SiO2 molar ratios (1:4, 1:1, and 4:1), prepared employing a sol-gel method modified by an original procedure. The evolution of ZnO-SiO2 systems depending on the composition and temperature was studied by thermal analysis, Fourier transform infrared spectroscopy, X-ray diffractometry and transmission electron microscopy. Zn(II) carboxylate was synthesized in situ in hybrid silica gels by redox reaction between zinc nitrate and 1,3-propanediol. Its thermal decomposition at low temperatures led to ZnO dispersed in the pores of silica matrix. Only for the 4:1 system, at 400 and 600 °C, ZnO nanocrystallites (average size ∼9 nm) embedded in the amorphous silica matrix were obtained, the other systems being amorphous. Whatever the mixture composition is, above 600 °C, ZnO reacts with SiO2 to form zinc silicate. At 800 °C, for both 1:4 and 1:1 systems, poor crystallized β-Zn2SiO4 and α-Zn2SiO4 phases embedded in silica matrix were formed. Increasing the temperature, at 1000 °C, only for 1:1 system, β-Zn2SiO4 phase turned into single phase α-Zn2SiO4 (average crystallites size 28.3 nm). For 4:1 composition, at 800 and 1000 °C, systems consisting of ZnO and α-Zn2SiO4 nanocrystallites dispersed in silica were obtained.