Facet-selective growth of MOF-on-MOF heterostructures enables etching-free synthesis of highly-open Co/N-doped carbon nanoframes for efficient catalysis

Highly-open nanoframe structures consisting of interconnected and exposed ridges are highly desirable for achieving efficient catalysis, but preparing them by a facile etching-free methodology is still a very daunting task. Herein, we propose a novel metal-organic framework (MOF)-assisted and etching-free strategy for the construction of Co/N-doped carbon nanoframes with highly-open and precisely-controllable structures. This strategy is based on the face-selective epitaxial growth of ZIF-67 on the 36 {110} facets of 72-facet ZIF-8 to form an unprecedented anisotropic ZIF-67-on-ZIF-8 heterostructure, which is subsequently pyrolyzed under Ar atmosphere to realize a solid-to-frame transformation. The highly-open nanoframe structure enables the substrates to readily penetrate into the catalyst interior and thereby create additional exposed active sites, which together with the good mass transport, high atomic utilization and increased surface area are responsible for its remarkably enhanced catalytic activity for the biomass valorisation when compared with its solid and closed hollow counterparts. This study could shed valuable insights into the design and preparation of various highly-open nanoframes with abundant exposed active species by using an etching-free strategy for efficient catalysis and beyond.