Synthesis and characterization of nanocrystalline Mn-Zn ferrites obtained via hydrothermal method using Aloe barbadensis Mill (Asphodelaceae) extract for the treatment of water contaminated with Congo red

Nanocrystalline ferrites of the Mn_1-xZn_xFe₂O₄ system (x = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) were synthesized with varying Mn and Zn contents using a hydrothermal method assisted with Aloe barbadensis Mill (Aloe vera) extract as adsorbent materials in the treatment of water contaminated with an azoic organic dye (Congo red). The obtained nanoferrites were subjected to morphological, magnetic, optical and thermal characterization using SEM, XRD, FTIR, VSM, UV–Vis, DLS and TGA techniques. Nanocrystalline ferrites with a spinel-type structure and crystallite sizes ranging from 19.5 to 42.1 nm were obtained from XRD analysis. Morphological analysis by SEM revealed agglomerates of irregularly shaped particles with nanometric sizes. Magnetic hysteresis curves obtained by VSM showed the magnetically soft behavior of the ferrites, with saturation magnetization values ​​Ms between 37.89 and 8.78 emu/g, which decrease with increasing Zn content. UV–vis spectra confirmed that ferrites absorb primarily in the ultraviolet region and that the band gap energy increased with the addition of Zn. The Congo red dye adsorption tests showed that Mn-Zn ferrites perform well as adsorbents. Of all the compositions, the ferrite with x = 0.0 achieved a dye removal efficiency of 73.65 % across varying the concentration (25 ppm) and contact time (20 min). Likewise, this ferrite with x = 0.0 reached a maximum Congo red adsoprtion of 84 % at pH 5. Meanwhile, the ferrite with x = 1.0 achieved a dye removal efficiency of 74.84 % at pH 7. These results prove that Mn-Zn ferrites synthesized from Aloe vera extract represent a sustainable and efficient alternative for the treatment of water contaminated with the Congo Red dye.