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.