Green synthesis of Fe⁰ nanoparticles using Eucalyptus grandis leaf extract: Characterization and application for dye...

Zero-valent iron nanoparticles (EGnZVI) were synthesized using Eucalyptus grandis (EG) leaf extract as a reducing/stabilizing agent. The studied materials (EG leaves, extract and EGnZVI) were characterized using the XRD, FTIR, Raman spectroscopy, SEM, TEM/EDS techniques. The results indicate that several organic compounds, including phenolics, present in the EG leaves were successfully extracted and incorporated into the structure of the material, possibly promoting the capping and stabilization of the formed zero-valent iron particles. The EGnZVI presented low crystallinity, varied size (50-500 nm), approximately spherical shape, and formed aggregates. The EGnZVI were utilized in the removal of the Direct Red 80 (DR80), an azo dye. The effects of the temperature (15-35 °C), initial DR80 concentration (10-250 mg L^-1), initial pH (2.5-8.5), the doses of H₂O₂ (0.5-5 mmol L^-1) and EGnZVI (0.2-10 mg L^-1), and the incidence of UV-light were evaluated. The EGnZVI did not present reactivity towards the DR80 in the absence of H₂O₂. However, in the presence of H₂O₂, the EGnZVI was highly efficient at removing the DR80 at slightly acidic pH₀ values (4 and 5.5). Under these pH₀ conditions, the EGnZVI/Fenton process proved to be more effective than the classic homogenous Fenton. Finally, in the presence of the UV-light, the process was highly efficient throughout the studied pH₀ interval, with increased removal rates. Therefore, the nZVI/Fenton process, using the synthesized material, presents itself as a promising alternative for the degradation of organic pollutants, and the incidence of UV light can considerably improve its efficiency.