Shape controlled synthesis of nanostructured magnesium oxide particles in supercritical carbon dioxide with ethanol cosolvent

• Artificial control of magnesium compound nanoarchitectures via carbonation reaction.
• Morphological changes were driven by phase transition during a solvothermal process.
• Micro-meso porous magnesium oxide architectures with high surface area were formed.

Magnesium compound nanoarchitectures with controlled shape were prepared through carbonation reaction of magnesium hydroxide and carbon dioxide in supercritical carbon dioxide–ethanol mixtures and their formation mechanism were discussed. The leaf-like brucite and the floral-like hydromagnesite nanosheets with a monoclinic structure were formed at the reaction temperature of less than 80 °C and 100 °C, respectively. The floral architecture started to transform the nanosheets with stacked arrangements at the elevated temperature above 130 °C, and compeletely transformed to cube-like magnesite with a trigonal crystal structure at 150 °C in progress of the carbonation reaction of hydromagnesite and carbon dioxide in a supercritical CO2 with ethanol cosolvent. The morphologies of the product architectures were artificially controlled by the phase transition driven morphological changes. With further increasing temperature to 600 °C, the micro–meso porous magnesium oxide architectures with high surface area were finally formed by decarbonation of the magnesite cubes.

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