Enhancing lead and cadmium ions adsorption efficiency using a low-cost hybrid adsorbent: banana peel modified with iron oxide nanoparticles

This research has prepared an eco-friendly alternative magnetic adsorbent, which removed lead (Pb+2) and cadmium (Cd+2) ions from aqueous solutions via the co-precipitation. The banana peels were impregnated with magnetic iron oxide (Fe3O4) nanoparticles before using them as an adsorbent to increase their efficiency for adsorption as well as for magnetic separation. A comparison between Fourier Transforms Infrared Spectroscopy (FTIR) analysis revealed a diminished peak corresponding to carbonyl (C=O) at 1740 cm−1 and a new peak appearing at 570 cm−1 which confirms the presence of the Fe-O bond thus supporting the successful immobilisation of the nanoparticle. The X-ray diffraction pattern showed the crystalline phase of Fe3O4, while scanning electron microscopy illustrated the fairly distributed nanoparticles on the peel surface. Both pH variations and initial concentration of ions along with contact time were considered. The optimum conditions were found when the pH was 5.0, a contact time of 90 minutes was enriched with 0.1 grams of adsorbent, using 50 mL of solution having an initial concentration of 50 mg/L, and showed maximum removal efficiencies of 98.6% Pb+2 and 94.3% Cd+2. Kinetic modelling data suggested that the process followed pseudo-second-order kinetics (R2 > 0.995). The composite showed a greater advantage over the raw banana peel and Fe3O4 alone with regard to magnetic separation ability and reuse, up to five cycles with above 85% efficiency, with negative ΔG° values (−5.82 to −7.75 kJ/mol) and positive ΔH° (106.45 kJ/mol) and ΔS° (25.91 J/mol·K), so the adsorption process was spontaneous and endothermic.