Nitrogen-doped carbon nanotube encapsulated Co9S8 composite cathode for high-selective capacitive extraction of uranium (VI) from radioactive wastewater

Selective extraction of uranium [U(VI)] from uranium containing nuclear wastewater is of great significance in alleviating the uranium resources shortages and eliminating the radioactive radiation. Benefited by the merits of cost-effectiveness and environment-friendliness, capacitive deionization (CDI) showed a great promise towards selective removal of U(VI). However, exploring novel electrode materials with high intrinsic affinity rather than the excessive assistance of external means faces challenges. Herein, a nitrogen-doped carbon tube encapsulated Co9S8 composite (CS-NCNT) was developed as a Faradic cathode for selective electrosorption of U(VI) from radioactive wastewater. This work mainly emphasized on these following results: (i) The electrochemical redox activity and high surface-controlled ratios endowed the optimized CS-NCNT-2 electrode a maximum electrosorption capacity (189 mg g−1) towards U(VI). (ii) Except that CS-NCNT-2 exhibited excellent selective electrosorption performance in U(VI)-containing spiked real seawater, an ultrahigh selectivity coefficient of 707 (UO22+ over Na+) was also achieved at a Na+: UO22+ molar ratio of 200. (iii) The valence state analysis and molecular dynamic simulation revealed the essence of the reversible electrosorption-desorption process and the preferable extraction towards UO22+ compared with Na+ ions, respectively. Overall, this work can be potentially expanded to other metal chalcogenides-based electrode materials for selective removal of UO22+ even other radionuclide in U(VI)-containing radioactive wastewater.