Fe3O4 Nanopowder under the Effect of Conventional Ultrasonication Treatment

Abstract

A new study was conducted to assess the actual effect of ultrasonication, a highly common treatment used to desegregate and deagglomerate nanoparticles for their subsequent dispersion in different media. In particular, Fe3O4 conventional magnetite nanoparticles suspended in a solvent (acetone) were subjected to a sonication process at different temperatures (0 °C and room temperature) for different times (15, 30, 45, and 60 min). It was found that there is a clear change in the nanoparticles in terms of their size and shape. This distinction is critical because changes in nanoparticle size may arise either from deagglomeration of loosely bound clusters or from actual fragmentation/erosion of primary particles, which implies a fundamentally different physical mechanism and different consequences for material performance. Notably, particle size rapidly decreases with sonication time, which was further enhanced by a drop in temperature. Additionally, the shape of the particles is modified from the initial truncated cubes typical of spinel ferrite nanoparticles to octahedra due to a process of wear. Based on the observed evolution toward an octahedral morphology, we infer that the relative removal rates of crystallographic facets change during ultrasonication. However, the present study does not directly measure facet-resolved erosion, and thus, it can only be hypothesized that the removal of (111) planes of atoms occurs as a consequence of higher interplanar spacing. All these results highlight the need to carefully reconsider the use of the ultrasonication process to achieve better dispersions of nanoparticles within polymer matrices to obtain nanocomposite materials without altering their dimensions. These findings suggest that ultrasonication-induced cavitation not only promotes deagglomeration but also may induce fragmentation/erosion of primary particles with surface atom removal, leading to thermodynamically driven shape evolution, with important implications in nanocomposite design, since many studies implicitly assume that ultrasonication does not alter intrinsic nanoparticle properties, potentially leading to misinterpretation of structure−property relationships.