Exploration of selective copper ion separation from wastewater via capacitive deionization with highly effective 3D carbon framework-anchored Co(PO3)2 electrode

The increasing amount of heavy metal copper ions (Cu 2+ ) in industrial emissions, poses a serious threat to human health, biological environment, and resource scarcity. Capacitive deionization (CDI) is considered as a green and efficient method for desalination. It is crucial to develop high-performance electrodes for efficient operation of CDI that go beyond conventional carbon and yield considerable environmental benefits. Here, metal organic frameworks (MOFs) derived carbon-loaded cobalt metaphosphate (NC-Co(PO 3 ) 2 ) was prepared by low-temperature gas–solid phosphating for Cu 2+ removal as CDI electrode for the first time. NC-Co(PO 3 ) 2 demonstrated superior electrode structure and function due to the synergistic effects of electric double layer coupling P-O bonds, the binding tendency of metaphosphate groups with Cu 2+ , and interfacial redox reactions induced by the labile valence state of cobalt. The optimal electrosorption capacity of NC-Co(PO 3 ) 2 was 95.41 mg g −1 at 1 V in 50 mL Cu 2+ solution with splendid cyclic regeneration capability. Moreover, NC-Co(PO 3 ) 2 exhibited excellent selectivity and outstanding electrosorption performance in the presence of multiple coexisting ions and this CDI system realized the purification of actual copper-containing wastewater. A series of characterizations further revealed the specific mechanism of Cu 2+ in adsorption–desorption process. Our finding strongly supported NC-Co(PO 3 ) 2 electrode can extend the CDI platform's capability for effectively removing and retrieving Cu 2+ from wastewater.