MOF-on-MOF nanoarchitectures for selectively functionalized nitrogen-doped carbon-graphitic carbon/carbon nanotubes heterostructure with high capacitive deionization performance

Carbon-carbon heterostructures are an emerging material paradigm to promote the development of capacitive deionization (CDI). The synthesis of this heterostructure with designed functionalities derived from metal-organic frameworks (MOFs) is interesting, but it has always been challenging. We develop MOF-on-MOF nanoarchitectures to obtain a selectively functionalized nitrogen-doped carbon@graphitic carbon/carbon nanotubes heterostructure (NC@GC/CNTs) via the direct pyrolysis of elaborately designed ZIF-L@ZIF-67 core-shell precursors. In this core-shell nanoarchitecture, the inner Zn-based ZIF-L provides a well-defined 2D interface for the oriented growth of the Co-based ZIF-67 outer layer, which will then convert to NC nanosheets with a high nitrogen doping content and large specific surface area for the accommodation of more ions. Meanwhile, the outer ZIF-67 layer creates highly graphitized GC/CNTs architecture offering fast electron transfer and good chemical stability, and it addresses the possible aggregation or collapse of the inner ZIF-L precursors during pyrolysis. As expected, the newly developed NC@GC/CNTs material with well-designed functionalities exhibits high salt adsorption capacity, rapid salt adsorption rate, and excellent CDI cycling stability, which highlight the significance of the carbon–carbon heterostructure to potential CDI applications and the importance of MOF-on-MOF nanoarchitectures on nanomaterials synthetic chemistry.