Nanoreactor of MOF-Derived Yolk–Shell Co@C–N: Precisely Controllable Structure and Enhanced Catalytic Activity

Hollow yolk–shell nanoreactors are of great interest in heterogeneous catalysis owing to their improved mass transfer ability and stability. Here, we report a facile and straight route to synthesize a highly efficient and recyclable yolk–shell Co@C–N nanoreactor with controllable properties by the direct thermolysis of a hollow Zn/Co-ZIF precursor. Based on systematical optimization of the pyrolysis temperature and the shell-thickness of Zn/Co-ZIFs, we could completely anchor and stabilize uniform Co nanoparticles (NPs) in the hollow yolk, accommodated by the Co-ZIF derived N-doped carbon nanosheets. This nanosheet-assembled yolk was further confined by a permeable and robust N-doped carbon (C–N) shell to protect the Co NPs against leaching and also enabled the reaction to take place in the hollow void. Consequently, the optimal yolk–shell Co@C–N nanoreactor showed a significantly enhanced catalytic activity for the aqueous oxidation of alcohols, yielding >99% conversion under atmospheric air and base-free conditions, which was much higher than that of the solid counterparts derived from pure ZIF-67 and solid core–shell ZIF-67@ZIF-8 precursors (with 14% and 59% conversion under the same reaction condition, respectively). The enhanced catalytic activity should be attributed to the yolk–shell structure that could facilitate the transport of reactant/product and the strong interaction between the Co NPs and N-doped carbon nanosheet to afford positive synergistic effects. Moreover, this catalyst also showed good recyclability, magnetically reusability, and general applicability for a broad substrate scope, further highlighting the structure superiority of our yolk–shell nanoreactor. This strategy might open an avenue to synthesize various hollow yolk–shell nanoreactors with controllable structures and enhanced catalytic performances.