Chitosan-Fe₃O₄ Membranes for Biosorption of Cr(VI) in Water, and Study of its Degradation Using Entomopathogenic Fungi (Beauveria sp and Nomureae sp)

Among heavy metals, hexavalent Cr(VI), a potent carcinogen, is one of the most common residues generated by the mining and textile industry, causing a severe impact on the environment, animals, and human health. In this work, magnetic membranes based on chitosan and magnetite nanoparticles were prepared, and their performance in removing Cr(VI) from water was evaluated. Chitosan was obtained from shrimp shell waste, while magnetite nanoparticles were synthesized by the TREG-mediated solvothermal method. Materials were characterized by XRD, FTIR, UV–Vis, DLS, and SEM–EDS. Quasi-spherical nanoparticles of 10 nm size were obtained with relatively low agglomeration and good magnetization (65 emu/g) properties. The membranes containing 4.8% w/w of magnetic NPs removed up to 90% of Cr(VI) from water after 40 min. These results suggest that a good dispersion of these magnetic nanostructures within the chitosan matrix generates a composite membrane with a homogeneous distribution of biosorption sites useful for Cr(VI) aqueous remotion. The elemental analysis combined with the micrographs indicated that adsorbed chromium was only present where Fe₃O₄ NPs were located and nowhere else. Importantly, after Cr(VI) remotion, the chitosan membranes were degraded by Beauveria sp and Nomureae sp fungi, showing the complete process of formation-biosorption-degradation in a couple of weeks.