A general strategy for direct growth of yolk-shell MOF-on-MOF hybrids

Construction of metal–organic framework (MOF) hybrids with yolk-shell nanostructures via MOF-on-MOF growth is significant for MOF design toward elaborate properties and enhanced performances, while remains challenging. Here, we report the direct growth of yolk-shell MOF-on-MOF hybrids via an interfacial growth-reorganization strategy. The synthesis relies on the precise growth of guest CoZn-ZIF (ZIF = zeolite imidazole framework) with appropriate crystal diameter and arrangement on host MOFs, inducing an in-situ transformation of core–shell intermediate into yolk-shell product. This strategy can be generally applied to the growth of CoZn-ZIF onto various host MOFs with different shapes, crystal structures and compositions including rod-like and octahedral Fe-based NH₂-MIL-88B (MIL = Material Institute Lavoisier) and cake-like Ti-based NH₂-MIL-125 toward three kinds of yolk-shell MOF-on-MOF hybrids. Moreover, functional carbon materials with bridged yolk-shell architecture can be prepared by pyrolysis of MOF-on-MOF hybrids as precursors, exhibiting enhanced oxygen reduction reaction performance than their monomeric counterparts. Our work paves the way for the design and application of MOF based yolk-shell nanostructures.