Synthesis, Characterization, and Adsorption Studies of Nanocrystalline Aluminum Oxide and a Bimetallic Nanocrystalline Aluminum Oxide/Magnesium Oxide

Abstract

Nanocrystals of Al 2 O 3 and Al 2 O 3 /MgO have been produced by a modified aerogel synthesis involving the corresponding aluminum tri- tert -butoxide, magnesium methoxide, toluene, methanol, ethanol, and water. The resulting oxides are in the form of powders having crystallites of about 2 nm or less in dimension. These crystallites have been studied by transmission electron microscopy (TEM), and Brunauer−Emmet−Teller (BET) methods, and were found to possess high surface areas and pore volumes (800 m 2 /g for Al 2 O 3 and 790 m 2 /g for Al 2 O 3 /MgO, compared to 450 m 2 /g for MgO). As seen with other metal oxides, once they are produced as nanoparticles, their reactivity is greatly enhanced on a per unit surface area basis. This is thought to be due to morphological differences, whereas larger crystallites have only a small percentage of reactive sites on the surface, smaller crystallites possess much higher surface concentration of such sites per unit surface area. Elemental analysis, X-ray diffraction, and infrared spectroscopy have been used to characterize these nanoparticles, and reactions with CCl 4, SO 2, and Paraoxon have demonstrated significantly enhanced reactivity and/or capacity compared with common commercial forms of the oxide powders. A significant feature is that, by a cogellation synthesis, Al 2 O 3 and MgO have been intermingled, which engenders enhanced reactivity/capacity over the pure forms of nanoscale Al 2 O 3 or MgO toward a chemical warfare surrogate (Paraoxon) and an acid gas (SO 2 ). This serves as an example where tailored synthesis of a nanostructured formulation can yield special benefits.