Magnetic properties, phase evolution, hollow structure and biomedical application of hematite (alpha-Fe2O3) and QUAIPH

We investigate synthesis, phase evolution, hollow and porous structure and magnetic properties of quasi-amorphous intermediate phase (QUAIPH) and hematite (alpha-Fe2O3) nanostructure synthesized by annealing of akaganeite (beta-FeOOH) nanorods. It is found that the annealing temperature determines the phase composition of the products, the crystal structure/size dictates the magnetic properties whereas the final nanorod morphology is determined by the starting material. Annealing of beta-FeOOH at similar to 300 degrees C resulted in the formation of hollow QUAIPH nanorods. The synthesized material shows low-cytotoxicity, superparamagnetism and good transverse relaxivity, which is rarely reported for QUAIPH. The QUAIPH nanorods started to transform to porous hematite nanostructures at similar to 350 degrees C and phase transformation was completed at 600 degrees C. During the annealing, the crystal structure changed from monoclinic (akaganeite) to quasi-amorphous and rhombohedral (hematite). Unusually, the crystallite size first decreased (akaganeite -> QUAIPH) and then increased (QUAIPH -> hematite) during annealing whereas the nanorods retained particle shape. The magnetic properties of the samples changed from antiferromagnetic (akaganeite) to superparamagnetic with blocking temperature TB = 84 K (QUAIPH) and finally to weak-ferromagnetic with the Morin transition at TM = 244 K and high coercivity HC = 1652 Oe (hematite). The low-cytotoxicity and MRI relaxivity (r(2) = 5.80 mM(-1) s(-1) (akaganeite), r(2) = 4.31 mM(-1) s(-1) (QUAIPH) and r(2) = 5.17 mM(-1) s(-1) (hematite)) reveal potential for biomedical applications. (C) 2022 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.

Automated summary

This study investigates the synthesis, phase evolution, crystal structure, magnetic properties, and potential biomedical applications of QUAIPH and hematite nanostructures synthesized by annealing beta-FeOOH nanorods. The results show the relationship between annealing temperature, crystal structure, morphology, and magnetic properties of the synthesized materials, as well as their low cytotoxicity and high MRI relaxivity.