Abstract
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.
Highlights
Silica aerogels are extremely low density and highly porous materials that feature a 3-dimensional randomly organized network of silica nanoparticles filled with air, constituting up to 98% of the total weight (Gesser and Goswami, 1989; Dorcheh and Abbasi, 2008)
All the aerogels studied in this work show similar Thermo-gravimetric analysis (TGA)/differential scanning calorimetry (DSC) curves, in agreement with previous studies (Loche et al, 2010), even if in this case a surfactant was used
We showed the synthesis and characterization of novel CeO2-SiO2 aerogel nanocomposites where ceria nanoparticles were crystallized within the nanoporous architecture of the silica aerogel
Summary
Silica aerogels are extremely low density and highly porous materials that feature a 3-dimensional randomly organized network of silica nanoparticles filled with air, constituting up to 98% of the total weight (Gesser and Goswami, 1989; Dorcheh and Abbasi, 2008). CeO2 Nanoparticles in SiO2 Aerogel have a high potential as a support for heterogeneous catalysts for gas-phase reactions In this field, nanocomposite aerogels featuring a transition metal or metal-oxide nanophase dispersed within the backbone of the porous silica matrix are proposed, taking advantage of the properties of both the porous aerogel and the dispersed nanophase (Amonette and Matyáš, 2017). We present the synthesis and characterization of new CeO2-SiO2 aerogels These nanocomposites were synthesized with the aforementioned 2-steps acid-base catalyzed co-gelation protocol that yields aerogels with an extensive control over the loading and dispersion of the ceria nanoparticles. The use of dodecanoic acid (or hexanoic acid) as surfactant was needed during the synthesis to ensure a homogeneous dispersion of the ceria nanoparticles, and to control their growth We demonstrate that these new CeO2-SiO2 aerogel composites show exemplary thermal stability, even when submitted to thermal treatments in air at temperatures as high as 900◦C. Size distribution was determined using both bright and dark field images and sampling at least 100 particles per sample
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