Alkaline-Earth Oxide Nanoparticles Obtained by Aerogel Methods. Characterization and Rational for Unexpectedly High Surface Chemical Reactivities

Abstract

Aerogel preparation of MgO and CaO nanoparticles involves a sol−gel approach where methoxides are converted to hydroxide gels followed by hypercritical drying and vacuum dehydration. This produces, for these particular hydroxides/oxides, ultrafine particulates rather than monoliths. These particulate materials have exhibited unexpectedly high surface chemical reactivities that have allowed their successful use as high-capacity destructive adsorbents for toxic chemicals, including chlorocarbons, organophosphorus compounds, and acid gases. Detailed characterization involving X-ray diffraction (XRD), gas adsorption/pore distribution analysis, infrared, TEM, AFM, XPS, probe molecule adsorption, and elemental analysis has allowed a rationale to be developed that helps explain the high chemical reactivities observed, especially for CaO. Pore volume and size distribution, unusual surface morphologies with a high ratio of edge ion/surface ions, and trace residual (persistent) surface −OH and −OCH3 seem to be the main factors allowing these nanoparticulates to be isolable and stable and yet highly reactive, and results for CaO are emphasized herein.