Abstract
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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.