Synthesis of Micromesoporous Magnesium Oxide Cubes with Nanograin Structures in a Supercritical Carbon Dioxide/Ethanol Solution

Abstract

Micromesoporous magnesium oxide architectures with cubic morphologies were prepared via the chemical reaction of magnesium hydroxide in a supercritical carbon dioxide (CO(2))-ethanol system, and via the sequential thermal combustion of the reaction products. The morphological change to the cube shape from an irregular form was induced by the dehydoxylation-carbonation reaction of magnesium hydroxide with supercritical CO(2) at a reaction temperature of 150 degrees C, which leads to the greatly improved carbonation efficiency of magnesium hydroxide to magnesium carbonate. The precursor cubes with 3 similar to 5 mu m sizes were decarbonized and transformed into the nanocrystalline MgO phase with pore sizes of 1.3 similar to 6 nm after calcining at 600 degrees C. The micromesoporous cube with high surface area of 117.5 m(2)/g was obtained by the thermal decarbonation with phase transition from rhombohedral to cubic phase. As a result, nanograined magnesium oxide cubes with micromesoporous structures and high specific surface areas were formed by the carbonation reaction of the magnesium hydroxide with the supercritical CO(2), and the subsequent thermal decomposition of the magnesium carbonate cubes.