A comprehensive study on single and competitive adsorption-desorption of copper and cadmium using eco-friendly magnetite (Fe3O4) nanoparticles

The present study investigated the capability of magnetite nanoparticles (MNP) synthesized from the direct reduction iron sludge and green tea extract for the single and competitive adsorption of copper (Cu2+) and cadmium (Cd2+). Moreover, we assessed the desorption of Cu2+ and Cd2+ in a ten-day cycle (both single and competitive systems) to evaluate their release amount from the adsorbent’s surface. The adsorption process was described using three well-known adsorption isotherms: Langmuir, Freundlich, and Dubinin-Radushkevich. The Freundlich isotherm was employed to describe the desorption process. The maximum adsorption capacity of Cu2+ and Cd2+ by MNP according to the Langmuir curve was 21.24 and 19.36 mg/g, respectively. A significant difference was observed in the adsorbed value of heavy metals in the competitive mode and MNP selectively preferred Cu2+ against Cd2+. Results of energy-dispersive X-ray (EDX) and elemental mapping analyses corroborated the Cu2+ and Cd2+ adsorption in both single and competitive systems. The findings of Fourier-transform infrared spectroscopy (FTIR) analysis revealed the role of functional groups in Cu2+ and Cd2+ adsorption. The results of the desorption evaluation demonstrated the higher tendency of MNP to retain Cu2+ than Cd2+. We developed economical and environmentally friendly magnetite nanoparticles, promising in individual and competitive adsorption of Cu2+ from aqueous solutions while resisting to release it. Moreover, the adsorbent’s performance in singular removal of Cd2+ was noticeable.