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. - Highlights: • By modified sol-gel method, ZnO/SiO₂ and Zn₂SiO₄/SiO₂ nanocomposites were obtained. • ZnO dispersed in silica matrix results from zinc carboxylate thermal decomposition. • Zinc carboxylate was synthesized in situ in hybrid silica gels via redox reaction. • Evolution of ZnO in SiO₂ matrix depends on temperature and system composition.