Self-Assembling Peptide-Based Magnetogels for the Removal of Heavy Metals from Water

In this study, we present the synthesis of a novel peptide-based magnetogel obtained through the encapsulation of γ-Fe₂O₃-polyacrylic acid (PAA) nanoparticles (γ-Fe₂O₃NPs) into a hydrogel matrix, used for enhancing the ability of the hydrogel to remove Cr(III), Co(II), and Ni(II) pollutants from water. Fmoc-Phe (Fluorenylmethoxycarbonyl-Phenylalanine) and diphenylalanine (Phe₂) were used as starting reagents for the hydrogelator (Fmoc-Phe₃) synthesis via an enzymatic method. The PAA-coated magnetic nanoparticles were synthesized in a separate step, using the co-precipitation method, and encapsulated into the peptide-based hydrogel. The resulting organic/inorganic hybrid system (γ-Fe₂O₃NPs-peptide) was characterized with different techniques, including FT-IR, Raman, UV-Vis, DLS, ζ-potential, XPS, FESEM-EDS, swelling ability tests, and rheology. Regarding the application in heavy metals removal from aqueous solutions, the behavior of the obtained magnetogel was compared to its precursors and the effect of the magnetic field was assessed. Four different systems were studied for the separation of heavy metal ions from aqueous solutions, including (1) γ-Fe₂O₃NPs stabilized with PAA, (γ-Fe₂O₃NPs); (2) Fmoc-Phe₃ hydrogel (HG); (3) γ-Fe₂O₃NPs embedded in peptide magnetogel (γ-Fe₂O₃NPs@HG); and (4) γ-Fe₂O₃NPs@HG in the presence of an external magnetic field. To quantify the removal efficiency of these four model systems, the UV-Vis technique was employed as a fast, cheap, and versatile method. The results demonstrate that both Fmoc-Phe₃ hydrogel and γ-Fe₂O₃NPs peptide magnetogel can efficiently remove all the tested pollutants from water. Interestingly, due to the presence of magnetic γ-Fe₂O₃NPs inside the hydrogel, the removal efficiency can be enhanced by applying an external magnetic field. The proposed magnetogel represents a smart multifunctional nanosystem with improved absorption efficiency and synergic effect upon applying an external magnetic field. These results are promising for potential environmental applications of γ-Fe₂O₃NPs-peptide magnetogels to the removal of pollutants from aqueous media.