Functional Nanoporous Polyamide Aerogels
"Aerogels are low-density materials consisting of 3D assemblies of nanoparticles with high open porosities and surface areas. Inspired by the extraordinary mechanical strength of polymer crosslinked aerogels, our recent attention is focused on inexpensive multifunctional isocyanates reacting with a variety of aromatic, organometallic and inorganic monomers. Three such systems discussed here are: (A) Polymeric aerogels synthesized via a room temperature reaction of an aromatic triisocyanate with pyromellitic acid. Using solid-state CPMAS 13C and 15N NMR, it was found that the skeletal framework was a statistical co-polymer of polyamide, polyurea and polyimide. Stepwise pyrolytic decomposition followed by reactive etching of those components yielded microporous carbon aerogels with good gas sorption selectivities that may find application in CO2 capture and sequestration. (B) Ferrocene-polyamide aerogels prepared in one pot via reaction of an aromatic triisocyanate and ferrocene dicarboxylic acid. Upon pyrolysis (>̲800 °C / H2), monolithic Fe(0)-doped C-aerogels were obtained followed by quantitative transmetalation with noble metals (M: Au, Pt, Pd). The latter were demonstrated as heterogeneous catalysts in high yield reduction, oxidation and Heck coupling reactions. The monolithic catalysts were reused several times without loss of activity. (C) Polyureas formed via reaction of an aromatic isocyanate with several mineral acids, (H3BO3, H3PO4, H3PO3, H2SeO3, H6TeO6, H5IO6 and H3AuO3). The residual boron in the H3BO3 model system was very low (