Biosynthesis Scale-Up Process for Magnetic Iron-Oxide Nanoparticles Using Eucalyptus globulus Extract and Their Separation Properties in Lubricant–Water Emulsions

The use of natural organic extracts in nanoparticle synthesis can reduce environmental impacts and reagent costs. With that purpose in mind, a novel biosynthesis procedure for the formation of magnetic iron-oxide nanoparticles (IONPs) using <i>Eucalyptus globulus</i> extract in an aqueous medium has been systematically carried out. First, the biosynthesis was optimized for various extract concentrations, prepared by decoction and infusion methods, and yielded IONPs with sizes from 4 to 9 nm. The optimum concentration was found at 5% <i>w</i>/<i>v</i>, where the biosynthesis reaction time and ammonium hydroxide amount were the lowest of all samples. This extract concentration was tested, including in replicated samples, for a scale-up process, yielded a total mass of 70 g. It was found by Rietveld and electron microscopy analyses that the structural and morphological properties, such as crystalline and particle sizes (9 nm), are equivalent when scaling the synthesis process. ⁵⁷Fe Mössbauer spectroscopy results indicated that Fe ions are atomically ordered and in a trivalent state in all samples, corroborating with structural results found by X-ray diffraction. Magnetic analysis showed that the scale-up sample exhibited ferrimagnetic-like behavior suitable for magnetic remediation performance (55 emu g^-1). The eucalyptus functionalization was demonstrated by thermogravimetric measurements, whereas the colloidal analysis supported the stability of the magnetic suspensions at pH = 7 (zeta potential > -20 mV). The kinetic adsorption performance indicated a fast kinetic adsorption time of 40 min and remarkable removal efficiency of 96% for lubricant removal from water (emulsion systems). The infrared analysis confirmed the presence of the eucalyptus chemical groups even after the removal experiments. These results suggest that the scale-up sample can be recovered for future and sustainable magnetic remediation processes.