Synthesis of size-tuneable β-FeOOH nanoellipsoids and a study of their morphological and compositional changes by reduction
2019
Shape anisotropy has been shown to positively influence the performance of nanoparticles in many applications. Size-tuneable akaganeite (β-FeOOH) nanoellipsoids have been prepared and used as precursors
for producing anisotropic iron oxide nanoparticles by reduction. Nanoellipsoids with a size between 25–
235 nm in length and aspect ratio of 5 or 6, compatible for biomedical and catalytic applications, were
obtained by using different amounts and molecular weights of branched polyethyleneimine. The reaction
was scaled-up by a factor of two leading to a yield increase of 55%. Oleylamine or hydrazine was used to
reduce β-FeOOH nanoellipsoids at different reaction temperatures and times. With oleylamine at 200 °C,
the same nanoellipsoid shape was retained with clear voids, but the phase changed to oxide–hydroxide;
while at a higher temperature of 250 °C, the phase converted to iron oxide but the nanoparticles lost their
original morphology. In the case of hydrazine, with the presence of polyethyleneimine, goethite (α-FeOOH)
wires were formed, the amount of which is proportionally increased with time and concentration of the
polymer; without the latter, iron oxide particles were formed of variable shapes.
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