Growing CeO₂ Nanoparticles Within the Nano-Porous Architecture of the SiO₂ Aerogel

In this study, new CeO₂-SiO₂ aerogel nanocomposites obtained by controlled growth of CeO₂ nanoparticles within the highly porous matrix of a SiO₂ aerogel are presented. The nanocomposites have been synthesized via a sol-gel route, employing cerium (III) nitrate as the CeO₂ precursor and selected surfactants to control the growth of the CeO₂ nanoparticles, which occurs during the supercritical drying of the aerogels. Samples with different loading of the CeO₂ dispersed phase, ranging from 5 to 15%, were obtained. The nanocomposites showed the morphological features typical of the SiO₂ aerogels such as open mesoporosity with surface area values up to 430 m²·g^-1. TEM and XRD characterizations show that nanocrystals of the dispersed CeO₂ nanophase grow within the aerogel already during the supercritical drying process, with particle sizes in the range of 3 to 5 nm. TEM in particular shows that the CeO₂ nanoparticles are well-distributed within the aerogel matrix. We also demonstrate the stability of the nanocomposites under high temperature conditions, performing thermal treatments in air at 450 and 900°C. Interestingly, the CeO₂ nanoparticles undergo a very limited crystal growth, with sizes up to only 7 nm in the case of the sample subjected to a 900°C treatment.