Engineering Biocompatible Goethite Nanoparticles: Microstructural Tuning through Controlled Ferrihydrite Conversion Routes

Abstract

The goethite (α-FeOOH) nanoparticles (NPs) are highly attractive material with a broad spectrum of applications, including biomedicine thanks to a high thermodynamical stability. The formation and strict control of the phase-pure goethite NPs remain a challenging task due to the high sensitivity of the particles to the synthesis conditions. This study presents for the first time effect of the iron source (nitrate vs. chloride) and alkaline medium (NaOH vs. NH4OH) on three known distinct post-synthesis transformation pathways for preparing goethite NPs from ferrihydrite suspensions: aging, ultrasonic-assisted conversion, and hydrothermal crystallization. We observed that ferrihydrite NPs precursor generated from FeCl3 with NaOH facilitated the formation of phase-pure goethite through both aging and ultrasonic transformation under ambient conditions. In contrast, synthesis at 90 °C promoted the formation of larger crystals, often accompanied by significant phase impurities. For the first time, comprehensive characterization of the synthesized materials was performed in addition to previously used methods as X-ray diffraction, the 57Fe Mössbauer spectroscopy, transmission electronic microscopy, and low-temperature nitrogen adsorption/desorption enabling in-depth assessment of crystallinity, phase purity, and morphological features. These findings highlight the potential of iron-based goethite nanomaterials as safe, functional, and versatile platforms for future biomedical and technological applications.