Anisotropic PorousIron-Based Nanoparticles throughTwo-Step Hydrothermal and Hydrogen-Based Reduction: Enhanced MagneticPerformance for Potential Biomedical Applications

Iron-based nanoparticles have emerged as promising candidates for diverse biomedical applications, including cell separation, targeted drug delivery, hyperthermia therapy, and magnetic resonance imaging. This study reports the scalable synthesis of high-magnetization iron-based nanoparticles with controlled anisotropic shapes, achieved via a two-step process. Hematite nanoparticles, featuring nanocube, nanoellipse, and nanoneedle morphologies, were synthesized through the hydrolysis of ferric chloride in the presence of ammonium dihydrogen phosphate, with the morphology precisely tuned by adjusting reagent concentrations. These hematite nanoparticles were subsequently reduced in a hydrogen-based direct reduction at 480 °C, yielding iron-magnetite nanocomposites that retained their anisotropic shapes, exhibited significant porosity, and achieved an exceptional saturation magnetization of 207 emu/g - approximately 150% higher than conventional magnetite nanoparticles. Comprehensive characterization via SQUID magnetometry, Mössbauer spectroscopy, Rietveld refinement of X-ray diffraction data, and XPS for surface analysis confirmed the formation of metallic iron nanoparticles covered by a magnetite shell. Biocompatibility studies demonstrated the biocompatibility of these nanoparticles across a wide concentration range, underscoring their suitability for biomedical applications.