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

The goethite (α-FeOOH) nanoparticles (NPs) are highly attractive material with a broad spectrum of applications, including biomedicine thanks to high thermodynamical stability. The formation and strict control of the phase-pure goethite remains a challenging task due to the high sensitivity of the particles to the synthesis conditions. This study presents a comparative analysis of three 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 with NaOH facilitated the formation of phase-pure goethite through both aging and ultrasonic transformation under ambient conditions. In contrast, at 90 °C promoted the formation of larger crystals, often accompanied by minor phase impurities. While the Cl- influenced structural evolution, our study underscores the dominant role of synthesis parameters, particularly thermal and temporal control, in dictating the phase selectivity and morphological uniformity of goethite. Notably, aging-based syntheses, without thermal or ultrasonic enhancement, consistently yielded homogeneous, monophasic crystals exhibiting complete sorption (with partition coefficients approaching). Comprehensive characterization of the synthesized materials was performed using X-ray diffraction, 57Fe Mössbauer spectroscopy, and transmission electronic microscopy, enabling a detailed assessment of crystallinity, phase purity, and morphological features.