1 research outputs found
Formation Mechanism of Maghemite Nanoflowers Synthesized by a Polyol-Mediated Process
Magnetic nanoparticles are being
developed as structural and functional
materials for use in diverse areas, including biomedical applications.
Here, we report the synthesis of maghemite (γ-Fe<sub>2</sub>O<sub>3</sub>) nanoparticles with distinct morphologies: single-core
and multicore, including hollow spheres and nanoflowers, prepared
by the polyol process. We have used sodium acetate to control the
nucleation and assembly process to obtain the different particle morphologies.
Moreover, from samples obtained at different time steps during the
synthesis, we have elucidated the formation mechanism of the nanoflowers:
the initial phases of the reaction present a lepidocrocite (γ-FeOOH)
structure, which suffers a fast dehydroxylation, transforming to an
intermediate “undescribed” phase, possibly a partly
dehydroxylated lepidocrocite, which after some incubation time evolves
to maghemite nanoflowers. Once the nanoflowers have been formed, a
crystallization process takes place, where the γ-Fe<sub>2</sub>O<sub>3</sub> crystallites within the nanoflowers grow in size (from
∼11 to 23 nm), but the particle size of the flower remains
essentially unchanged (∼60 nm). Samples with different morphologies
were coated with citric acid and their heating capacity in an alternating
magnetic field was evaluated. We observe that nanoflowers with large
cores (23 nm, controlled by annealing) densely packed (tuned by low
NaAc concentration) offer 5 times enhanced heating capacity compared
to that of the nanoflowers with smaller core sizes (15 nm), 4 times
enhanced heating effect compared to that of the hollow spheres, and
1.5 times enhanced heating effect compared to that of single-core
nanoparticles (36 nm) used in this work