Plant-Based Iron Nanomaterials Derived from <i>Ilex paraguariensis</i> for Heavy Metal Remediation

Iron-polyphenol nanoparticles (FePP NPs) were synthesized using an iron precursor and polyphenols from Ilex paraguariensis extract at varying molar ratios of iron-to-polyphenol (as the gallic acid equivalent, GAE). Nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, zeta potential measurements, and transmission electron microscopy. Cr(VI) removal (25 mg·L–1) was evaluated through batch experiments after 80 min at varying Fe(III)/GAE ratios, nanoparticle doses, pH values, and temperatures. At an Fe(III)/GAE ratio of 0.89, removal efficiency was 98.7% with 56 mg·L–1 nanoparticle dose, pH 4, and 25 °C (removal capacity of 400 mg·g–1) but dropped to 37% when the ratio was increased 6-fold and to 42% when the nanoparticle dose was decreased 5-fold. Removal efficiency was only slightly affected by the pH and temperature. Kinetics followed a pseudo-second-order model (Adj R2 ≥ 0.98; NSD% ≤ 4.22). Postexperiments, electron energy-loss spectroscopy revealed near-complete oxidation of iron and reduction of chromium, with the latter largely adsorbed onto nanoparticle clusters as evidenced by energy filtering transmission electron microscopy. These results demonstrate that FePP NPs synthesized with I. paraguariensis efficiently remove Cr(VI) across wide pH and temperature ranges, highlighting their potential for environmental applications.