Morphology evolution of exfoliated trimanganese tetroxide nanosheets and mass transfer model of growth kinetics in supercritical N,N-dimethylformamide

• Particulate materials resulting from Mn3O4 nanosheets can grow into giant polyhedron.
• Mn ions become dense as the processing time increases in the growing course.
• Supercritical fluid provides the environment for a rapid growth of manganese oxides.
• There exist the phenomena of accelerated growth for manganese oxides in SC-DMF.
• A mass transfer model applicable to supercritical fluid surrounding is proposed.

Trimanganese tetroxide (Mn3O4) nanosheets can evolve into various morphologies in supercritical N,N-dimethylformamide (SC-DMF), including particulate materials, triangle, rhombus, cube, and other regular polyhedrons. The obtained polyhedrons have sizes from hundred nanometers to several micrometers (1–3 μm), along with a growing course. The phases are changed from Mn3O4 to MnO, as the processing time increases. The growth of manganese oxides in SC-DMF has a rate of 28.7–61.5 nm·min− 1. The phenomena of accelerated growth for manganese oxides in supercritical fluid are discovered. The growth kinetics of manganese oxides is performed by the classical Lifshitz–Slyozov–Wagner (LSW) model. A mass transfer (MT) model of growth kinetics applicable to supercritical fluid surrounding is proposed. Solubility and diffusion, as main factors, are included in the proposed model. The theoretical model and the fitting curve are in accordance with experimental results. The growth of manganese oxides in SC-DMF satisfies the first-order kinetics, obeying the exponential law.

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