Green synthesis of iron nanozymes using Eucalyptus grandis extract and their application as peroxidase-like catalysts for H₂O₂ quantification

In this work, iron nanoparticles were synthesized by a green and bio-inspired process, using Eucalyptus grandis extract as a reducing and stabilizing agent. The functional groups from the extract were incorporated into the structure of the nanoparticles, as confirmed by infrared spectroscopy. Characteristic peaks of zero-valence iron were observed by X-ray diffraction analysis, besides hematite and goethite. The nanoparticles showed spherical morphology and an average size of 96.4 nm. The zeta potential (|35| mV) indicated good stability. The nanoparticles were used as catalysts for o-phenylenediamine oxidation by H₂O₂, exhibiting optimal catalytic activity. The kinetic assays were performed, and the Michaelis-Menten model was adjusted to the data (maximum rate reached (V_max) = 2.0 μmol L^-1 s^-1 and Michaelis-Menten constant (Km) = 307 μmol L^-1). A spectrophotometric method was developed for H₂O₂ quantification. The analytical curve (18.3-112.6 μmol L^-1) showed a good linear fit and limits of detection and quantification of 5.48 and 18.3 μmol L^-1, respectively. Thus, the method is very promising, adhering to the principles of green chemistry. (author)