Carbonation reaction from the dissolution of minerals, mainly silicates, is an option for long-term storage of CO 2 , offering capacity exceeding that of other strategies, and certain advantages such as the formation of insoluble and inert products. This study presents the results of carbonation reactions utilizing silica aerogelwollastonite composites. The procedure for synthesis of the precursor powders with wollastonite stoicheiometry, as well as the compositional and textural features of the resulting composites, was examined first. The kinetic and efficiency of carbonation reactions in aerogel-wollastonite composites were also determined. X-ray diffraction quantitative analysis and thermogravimetric analysis were used to determine the proportions in percent of the resulting carbonate phases. The conversion reaction reaches values above 81% in composites with CaO content of up to 40% by weight, after 40 min of reaction time. The conclusion is that these aerogels, offering a very high specific surface area, are attractive potential materials for CO 2 sequestration and as a supporting material for fast carbonation reactions.

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Hybrid sono-aerogels in the CaO−SiO2−poly(dimethyl siloxane) (PDMS) system with low density and high surface area and pore volume were investigated to be used as biomaterials. Their in vitro bioactivity was monitored by soaking in a simulated body fluid (SBF). All the aerogels exhibited similar wetting and dissolution properties, but only the aerogel of composition 20 wt % PDMS−20 wt % CaO (S20Ca20) exhibited a bioactive response in SBF. To investigate the relationship between the different in vitro behaviours and the hybrids nanostructure, samples were studied by high-resolution transmission electron microscopy (HRTEM). All the aerogels showed similar basic microstructural features exhibiting amorphous Ca-free areas characterized by Si−O−Si distances of 0.23 nm. However, crystallized nanodomains containing calcium were also detected in S20Ca20. These domains, identified as pseudowollastonite and other Ca−Si−O phases, could explain the bioactive response of this material. Bioactivity and good textural and mechanical properties turn S20Ca20 aerogel into a candidate as biomaterial.

Organic-inorganic hybrid materials were synthesized by controlled hydrolysis of tetraethoxysilane (TEOS), methyltrimethoxysilane (MTES), synthetic wollastonite powders and polydimethylsiloxane (PDMS) in an ethanol solution. Aerogels were prepared from acid hydrolysis of TEOS and MTES with different volume ratio in ethanol, followed by addition of wollastonite powder and PDMS in order to obtain aerogels with 20 wt% of PDMS and 5 wt% of CaO of the total silica. Finally, when the wet gels were obtained, they were supercritically dried at 260 degrees C and 90 bar, in ethanol. In order to obtain its bioactivity, one method for surface activation is based on a wet chemical alkaline treatment. The particular interest of this study is that we introduce hybrid aerogels, in a 1 M solution of NaOH, for 30 s at room temperature. We evaluate the bioactivity of TEOS-MTES aerogel when immersed in a static volume of simulated body fluid (SBF). An apatite layer of spherical-shaped particles of uniform size smaller than 5 microns is observed to form on the surface of the aerogels after 25 days soaking in SBF.

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