Abstract
Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 × 103 m2/mol, with pore volumes in the order of 70 cm3/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180–250 °C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.
Highlights
Iron oxide nanoparticles are available nowadays in a variety of shapes and are technologically important components widely used for the production of, e.g., magnetic materials [1,2,3], color pigments [4,5], catalysts [6], sorbents [7,8], for biomedical applications and drug delivery [3,9,10,11,12], as well as being key components in the Martial soil [13]
We have studied the transformation of lepidocrocite nanoprisms into porous maghemite nanoprisms
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Summary
Iron oxide nanoparticles are available nowadays in a variety of shapes and are technologically important components widely used for the production of, e.g., magnetic materials [1,2,3], color pigments [4,5], catalysts [6], sorbents [7,8], for biomedical applications and drug delivery [3,9,10,11,12], as well as being key components in the Martial soil [13]. Synthetic lepidocrocite nanoparticles offer an opportunity to study pore formation in iron (oxy)hydroxides. Giovanoli and Brutsch [25] suggested that lepidocrocite layers collapse in such a way that more edge and corner sharing O2− ions become available to form H2O on the one hand and form a ccp of O2− on the other hand. Both processes involve a strain in the lattice whereby pores form to at least partly compensate for the lattice distortion. Prolongation of the heating leads to the coalescence of micropores to mesopores and macropores
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