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

Abstract

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