Fabrication of Fe-CoS2@N-doped C electrode for highly efficient and durable electrosorption of Yb(III) from aqueous solutions

In this study, the novel Fe-doped CoS2@nitrogen-doped carbon (Fe-CoS2@NC) composites were manufactured and investigated as the capacitive deionization (CDI) electrode materials for electrosorption of Yb(III). The as-prepared materials were characterized with X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, N2 adsorption–desorption test with Brunauer-Emmett-Teller method, Raman spectroscopy, and X-ray photoelectron spectroscopy. The electrochemical tests, including cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy, revealed that Fe-CoS2@NC exhibited the better electrochemical performance with a specific capacitance of 58.41 F g−1 than Fe-CoS2@0.5NC and Fe-CoS2. The electrosorption results demonstrated that Fe-CoS2@NC possessed the Yb(III) uptake of 129.4 mg·g−1 within 60 min at a voltage of 1.2 V and a flow rate of 20 mL·min−1. After five successive sorption–desorption cycles, the electrosorption efficiency of Fe-CoS2@NC remained at 98 %, exhibiting the robust durability for future industrial application. Furthermore, Fe-CoS2@NC also showed the favorable electrosorption performance towards various rare earth ions, especially for heavy rare earth ions. The mechanism analysis indicated that the impressive electrosorption performance is attributed to the synergistic contribution by the electric double layers of carbonaceous matrix and the pseudo-capacitance that induced by the redox reactions of Fe atom.