Paving the way to Fe3O4 nano- and microoctahedra by dealloying Al-Fe binary alloys

The preparation, morphologies, and properties of Fe3O4 octahedra have attracted considerable attention, while their formation mechanism has been less investigated. In this study, Fe3O4 nano- and microoctahedra are prepared by dealloying Al–xFe (x = 5–25 at.%) alloys in NaOH aqueous solutions with different concentrations. The dealloying of Al[sbnd]15Fe in the 5-mol·L−1 NaOH solution provides the most regular Fe3O4 octahedra. Al13Fe4 in the precursor Al[sbnd]Fe alloy and appropriate concentration of OH– ions are dominant factors in the formation of Fe3O4 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 Fe3O4, while a highly concentrated solution enhances the reduction of oxides and produces α-Fe rather than Fe3O4. 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 Fe3O4 nuclei to octahedra. This fundamental understanding provides technological guidelines for the synthesis and morphology control of Fe3O4, being of significance in the development of functional nanoparticles.