Nature inspired synthesis of magnetite nanoparticle aggregates from natural berthierine.

We investigate the origin of the magnetite nanoparticle aggregates (MNAs) from the Peña Colorada iron-ore mining district (Mexico) to devise a nature inspired synthesis process. Three types of samples were used: natural MNAs recovered from the mine, concentrated magnetite microparticles as reference material, and thin berthierine films used to synthesize MNAs. The chemical, mineralogical, crystallographic and rock magnetic properties were determined by polarized microscopy, high-resolution transmission electron microscopy, electron microprobe, X-ray diffraction, Mössbauer spectroscopy, and thermomagnetic and hysteresis measurements. MNAs were synthesized in the lab with the following steps. We start with berthierine thin films, which are heated to temperatures between 495 and 510 °C leading to formation of numerous stable magnetite nanocrystals. They grow at a temperature above 650 °C. Space restrictions lead to the formation of dense MNAs. Smaller MNAs, <200 nm, with a Curie temperature of 650 °C, shows superparamagnetic behavior. While larger MNAs, >7 μm, show Curie temperature of 578 °C and ferromagnetic behavior. Based on present observations, we suggest that MNAs in the Peña Colorada iron-ore formed in a marine environment, where berthierine formation was accelerated by Fe-rich hydrothermal springs that supplied iron and increased the temperature. Most notably, our laboratory experiments mimicked natural conditions and were able to successfully nucleate and grow magnetite nanoparticles which developed into MNAs. These MNAs were similar to those recovered from the Peña Colorada iron-ore deposit. This study, thus, provides a nature inspired method for synthesis of magnetite nanoparticles and its aggregates.