Synthesis of size-tuneable β-FeOOH nanoellipsoids and a study of their morphological and compositional changes by reduction

Abstract

Shape anisotropy has been shown to positively influence the performance of nanoparticles in many applications. Size-tuneable akaganéite (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.