Ion-Selective Capacitive Deionization Enabled by Codoped Core–Shell Carbon Architectures for Efficient Uranium Recovery

Abstract

The targeted removal of U(VI) from radioactive wastewater with high efficiency and selectivity remains a pressing issue in environmental engineering. Herein, a hierarchical porous carbon material (CNC800) was developed via high-temperature pyrolysis of ZIF-67@ZIF-8 core–shell structures. The resulting composite possesses a hollow architecture with uniformly dispersed cobalt nanoparticles embedded within a conductive nitrogen-doped carbon matrix, providing abundant electroactive sites and facilitating rapid ion transport. Under a low-voltage capacitive deionization (CDI) process, CNC800 achieved a remarkable U(VI) removal efficiency of 94% and retained high performance with over 88% efficiency after five regeneration cycles. Competitive ion experiments confirmed its excellent selectivity toward U(VI) against various coexisting metal ions. Density functional theory (DFT) calculations revealed that the enhanced affinity originates from the synergistic coordination between cobalt centers and nitrogen functionalities, resulting in a strong adsorption energy of −2.99 eV, significantly exceeding that of conventional N-doped carbon (−1.33 eV). Notably, U(VI) exhibited the highest adsorption energy among all tested ions (Fe³⁺, Ni²⁺, Cr²⁺, Sr²⁺), highlighting its preferential interaction with CNC800. These findings demonstrate the great potential of CNC800 as a robust and selective CDI electrode material for U(VI) removal from low-concentration nuclear wastewater.