Synthesis and studies of transparent, monolithic polymer-silica hybrid aerogel materials

A new class of polymer-silica hybrid aerogels has been synthesized. The main component in each of these materials is silica. Other components include a bioorganic polymer and one or more metal ion species. When the polymer is chitosan, it has been incorporated homogeneously with the silica in aerogels and its functional groups can coordinate or at least immobilize the metal ions. The preparation of the polymer-silica hybrid aerogels involves the sol-gel process of an organo-silicon precursor in a polymer aqueous solution at a low pH. These reactions lead to the formation of silica network, with which the polymer component interpenetrates. It has been shown that the conditions of the sol-gel process are optimized in a way that the polymer component interacts with the growing silicate species to a large extent. Supercritical fluid extraction was used to transform those hybrid gels into transparent, monolithic hybrid aerogels. The physical characterization of these hybrid materials has been focused on investigating the microstructure, the effect of the incorporation of the polymer and information that would be useful for potential applications. The refractive indices of these materials were measured in the range 1.14–1.17. The BET surface areas range from 500 to 900 m2/g. The presence and coordination of transition metal ions in the aerogels are shown by Fourier transform infrared (FT-IR) and ultraviolet-visible spectroscopy. Near infrared spectroscopy was employed to measure the characteristic transitions of lanthanide ions in the hybrid aerogels. The magnetic susceptibility of Ru-containing hybrid aerogels was shown to decrease as the Ru content increased. Data from collaborative TEM, pore size distribution and SANS measurements, which revealed such structural information as the fundamental particle size, exponential fractal dimensions and cut-off length, were used to construct a model of the hybrid areogel structure. Reactions of Ru- and Rh-containing chitosan-silica aerogels with CO, NO, H₂ and H₂O were investigated. Specifically, the reactions of Ru(III)-chitosan-silica aerogels with CO and H₂O were studied at several different Ru concentrations. The coexistence of nitrosyls and carbonyls formed when NO and CO were reacted sequentially with Ru-chitosan-silica aerogels has helped to clarify the assignments of bands in infrared spectra. Potential applications of these hybrid aerogel materials have been explored. The photopolymerization of an acrylic monomer in aerogels was carried out, which has been shown to substantially increase the refractive index and to show how they could be used in holographic recording. A rate study of the partial hydrogenation of acetylene over Pd-chitosan-silica aerogels is also reported.