Improved size, morphology and crystallinity of hematite (α-Fe2O3) nanoparticles synthesized via the precipitation route using ferric sulfate precursor

Pure hematite nanoparticles (HNPs) were successfully synthesized via the simple precipitation route by using ferric sulfate precursor and ammonium hydroxide (NH4OH) precipitant. The current study reports the effects of precursor concentrations, from 0.05 to 0.45 M, on the product size, morphology, crystallinity, and lumps formation. X-ray diffraction (XRD) data confirmed the synthesis of pristine HNPs having a rhombohedrally centered hexagonal structure. In addition, the particle size effect on the XRD peak shifting was studied and found to be consistent with the calculated size results by Scherer equation. Transmission electron microscopy revealed mixed polygonal and hexagonal morphologies with an average size of (16–44 nm) depending on the precursor concentration. Scanning electron microscopy depicts lots of agglomerations and lumps with increasing the precursor concentration. Raman spectra not only show the seven phonon modes of pristine hematite phase but also confirm the evolution of the crystal structure with concentration. Thermal analyses proved that the synthesized α-Fe2O3 products in the current work using 0.05 M precursor concentration are well crystallized at around ≈464 °C. Thus, current work presents smaller-sized HNPs crystallized at lower temperature ranges with different morphologies and higher probable vulnerable facets compared to previous studies. This will show improved properties and give rise to higher potentials for various applications. Furthermore, it verifies that the precursor nature is the key factor affecting both size and morphology, whereas, precursor concentration not only affects the particle size as reported previously but also crystallinity, morphology development, and lumps formation of the final product. Keywords: Hematite (α-Fe2O3) nanoparticles, Chemical precipitation, Peak shifting, Crystallinity, Ferric sulfate precursor