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 (Vmax) = 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.