A general epoxide-assisted sol–gel route for the synthesis of metal oxide–silica composites and silicates ultrafine particles

A general sol–gel route using propylene oxide as a gelation agent was successfully applied to the synthesis of metal oxide–silica composites and silicates (2ZnO–SiO2, 3Al2O3–2SiO2 and CeO2–SiO2). Owing to the high homogeneity of the intermediate precursor gel obtained by this route, the target materials were obtained at low temperature and short time of calcination required to obtain the oxide phase. A short calcination time of 10 min was sufficient for the complete transformation of the precursors into the desired mixed oxide in all samples. Under this calcination conditions, the aggregation of the particles is minimized, allowing the preparation of small particles. Non-aggregated, nearly monodispersed CeO2–SiO2 composite nanoparticles with particle size of about 2 nm were obtained at 100 °C. ZnO–SiO2 composites can be obtained at 500 °C, which are transformed into non agglomerated Zn2SiO4 nanoparticles of 30–50 nm at 900 °C. Ultrafine mullite particles were obtained by a short calcination of the precursor gel at 1000 °C.