Adsorption Ability of Soft Magnetic FeCo Alloys for Microplastics

Abstract

Microplastics pose significant threats to human health and the environment, and environmentally friendly, efficient, and reliable technologies are needed to remove them from the environment. To explore the potential for metal nanoadsorbents to remove microplastics (MPs) from water, soft magnetic FeCo alloys were successfully synthesized and loaded onto carboxymethyl cellulose. The adsorption performance and mechanisms of soft magnetic FeCo alloys on typical microplastic pollutants, specifically polyethylene microplastics, were systematically studied. Characterization work performed through scanning electron microscopy, an X-ray diffraction analysis and Brunner−Emmett−Teller measurements (SEM, XRD and BET, respectively) confirmed that soft magnetic FeCo alloys possess a typical solid solution structure, abundant hydroxyl functional groups, and a high BET surface area of 142.8302 m2/g, providing sufficient active sites for MP adsorption. At 35 °C, the equilibrium adsorption capacity reached 120.92 mg/g, with a removal rate of 89.33% at a sufficient adsorbent concentration (0.5 g/L); the adsorption kinetics followed a pseudo-second-order kinetic model (R2 > 0.99). Additionally, the adsorption isotherm conformed to the Freundlich model (R2 = 0.969), demonstrating multilayer adsorption characteristics. Furthermore, X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy (XPS and FTIR analyses, respectively) indicated that the surface of FeCo is hydrophilic because of catalytic oxidation reactions, resulting in the exposure of polar groups (such as carboxyl and hydroxyl groups) on the microplastic surface, which form hydrogen bonds with oxygen or water molecules on the FeCo surface. The resulting redox vacancies provide ample active sites for the adsorption of microplastics. This study confirms the high microplastic adsorption capacity of soft magnetic FeCo alloys in aquatic environments.