Melissa Quevedo Lopez is a Colombian physicist and current Master’s student in Physical Sciences at Universidad del Atlántico. Her research focuses on the synthesis and characterization of Mn-Zn nanocrystalline ferrites for environmental applications, particularly in water treatment using green synthesis methods. She has extensive experience with experimental techniques such as X-ray diffraction, UV-Vis spectroscopy, SEM, TEM, FTIR, and DLS. Melissa has participated in international research programs, including at the University of Oslo and the University of Notre Dame, and has presented her work at numerous academic conferences across Latin America. Alongside her research, she is a dedicated educator, currently teaching physics at both secondary and university levels.
Pontificia Universidad Católica del Ecuador and Universidad de las Fuerzas Armadas (ESPE), Quito - Ecuador, February 2024 Research stay for the project "Synthesis and characterization of Mn-Zn nanocrystalline ferrites obtained via hydrothermal process from Aloe barbadensis Mill (Asphodelaceae) extract for the treatment of water contaminated with organic dyes." Characterization of nanoferrites was performed using Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR), Dynamic Light Scattering (DLS), and degradation tests on Congo red dye using ferrites as absorbent agents.
Synthesis and characterization of Mn-Zn nanocrystalline ferrites obtained via hydrothermal process from Aloe barbadensis Mill (Asphodelaceae) extract for the treatment of water contaminated with organic dyes
In this study, Mn1-xZnxFe2O4 nanocrystalline ferrites (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were synthesized by varying the compositions of Mn and Zn through the hydrothermal method, using Aloe barbadensis mill plant extract as an environmentally friendly solvent. From the various characterization techniques used—SEM, TEM, XRD, VSM, UV-Vis, TGA, DLS, FTIR—it was confirmed that the nanocrystalline ferrites are quasi-spherical in shape (SEM) and have an average size of 19.50 – 53.55 nm according to TEM. XRD analysis showed that all samples formed the characteristic spinel structure typical of these systems, with secondary phases (hematite Fe2O3) present except for the x = 0.6 sample. The average crystallite size ranged from 8.37 to 45.80 nm, and the lattice parameter ranged from 8.3862 to 8.453 Å. Magnetic hysteresis loops obtained by VSM demonstrated the soft magnetic behavior of the ferrites and the change in saturation magnetization with increasing Zn content. UV-Vis analysis showed an increase in the band gap with higher Zn content, and the ferrites absorbed in the UV spectrum. TGA analysis revealed mass loss due to the elimination of surface-adsorbed water or solvent. In the MnFe2O4 sample, the conversion of metal hydroxide (Mn and Fe) into metal oxide was observed. The results obtained from DLS corroborated the findings from SEM and TEM, showing that the ferrites were agglomerated, and the different distributions of the DLS hydrodynamic diameter ranged from 172.1 to 445.1 nm. FTIR analysis revealed the presence of different functional groups—OH, C-H, C=O from the aloe vera extract; the C-C group for the x=0.4 and x=1 samples, with the functional groups corresponding to those in the extract except for the band around 590 cm?¹ for x=0.4 and 548 cm?¹ for x=1.0, which are compatible with metal-oxygen vibrations in a tetrahedral lattice. The presence of polyphenols in the extract was confirmed by the Folin method, indicating that the ferrites were coated with aloe vera extract during synthesis. Finally, it was evaluated that the x=0.0 and x=1.0 compositions of the Mn1-xZnxFe2O4 system were the most effective for treating water contaminated with Congo red dye at the laboratory scale. Considering variables such as concentration, time, and pH, it was found that the best conditions were at concentrations above 100 ppm, with a treatment time of 30 minutes at pH 7 and pH 5.