Hydrothermal synthesis of hematite (α-Fe2O3) nanoparticle forms: Synthesis conditions, structure, particle shape analysis, cytotoxicity and magnetic properties

In this work, we present the magnetic and structural properties of alpha-Fe2O3 nanoparticles synthesized by the hydrothermal synthesis method. XRD, FTIR and Raman spectroscopy indicate that the samples consist of single-phase alpha-Fe2O3 nanoparticles. A microstructural analysis by TEM and SEM shows: (i) irregular nanoparticles (similar to 50 nm), (ii) plate-like nanoparticles (with thickness t similar to 10 nm and diameter d similar to 50 -80 nm) and (iii) microsized ellipsoid 3D superstructures (with length l similar to 3.5 and diameter d similar to 1.5 mu m) composed of nanosized building blocks (similar to 50 nm). We used circularity, elongation and convexity measures to quantitatively analyze the shape of the particles. Irregular hematite nanoparticles were synthesized using a water solution of ferric precursor and sodium acetate during the hydrothermal reaction (reaction conditions: T = 180 degrees C, t = 12 h). The same hydrothermal reaction temperature, reaction duration and ferric precursor (without sodium acetate) were used for synthesizing hematite ellipsoid 3D superstructures. Addition of urea and glycine surfactants in hydrothermal reaction resulted in the formation of nanoplate hematite particles. The role of these surfactants on the structure and morphology of the particles was also investigated. Magnetic measurements at the room temperature displayed a wide range of coercivities, from H-C = 73 Oe for irregular nanoparticles, H-C = 689 Oe for nanoplates to H-C = 2688 Oe for hematite ellipsoid 3D superstructures. The measured coercivity for the ellipsoid superstructure was about 35 times higher than in the case of irregular hematite nanoparticles and about 4 times than the coercivity of hematite nanoplates. Magnetic properties of synthesized samples were related to their structure and morphology. We conclude that shape anisotropy influenced enhancement of the coercivity in hematite nanoplates whereas hematite ellipsoid 3D superstructure (nanoparticle clusters) induced the formation of multidomain magnetic structure and highest coercivity revealing its superior structure for enhanced magnetic properties. The synthesized hematite nanoparticle structures exhibit low cytotoxicity levels on the human lung fibroblasts (MRC5) cell line demonstrating a safe use of these nanoparticles for practical applications. (C) 2019 Elsevier B.V. All rights reserved.