Paving the way to Fe3O4 nano- and microoctahedra by dealloying Al[sbnd]Fe binary alloys.

The preparation, morphologies, and properties of Fe 3 O 4 octahedra have attracted considerable attention, while their formation mechanism has been less investigated. In this study, Fe 3 O 4 nano- and microoctahedra are prepared by dealloying Al– x Fe (x = 5–25 at.%) alloys in NaOH aqueous solutions with different concentrations. The dealloying of Al 15Fe in the 5-mol·L−1 NaOH solution provides the most regular Fe 3 O 4 octahedra. Al 13 Fe 4 in the precursor Al Fe alloy and appropriate concentration of OH– ions are dominant factors in the formation of Fe 3 O 4 octahedra by changing the chemical potentials and growth rates along the 〈111〉 and 〈100〉 plane directions. A low concentration of NaOH solution deteriorates the anisotropic growth of Fe 3 O 4 , while a highly concentrated solution enhances the reduction of oxides and produces α -Fe rather than Fe 3 O 4. In addition to the experimental results, ab-initio molecular dynamics simulations are performed to reveal the evolutions of the surface energies and growth rates of different facets, depicting the formation trajectory from Fe 3 O 4 nuclei to octahedra. This fundamental understanding provides technological guidelines for the synthesis and morphology control of Fe 3 O 4 , being of significance in the development of functional nanoparticles. Unlabelled Image • Fe 3 O 4 nano- and microoctahedra are prepared by dealloying Al Fe alloys. • Both for Al Fe and NaOH, there is maxima composition producing regular octahedra. • Dealloying of Al 15Fe in 5-mol·L−1 NaOH produces the most regular Fe 3 O 4 octahedra. • Ab-initio MD simulations reveal the formation route to the Fe 3 O 4 octahedra. [ABSTRACT FROM AUTHOR]