Superlong Single-Crystal Metal–Organic Framework Nanotubes

Nanotubes have attracted great attention. Here, we report the fabrication of the first single-crystal metal–organic framework (MOF) nanotubes. Superlong single-crystal cobalt–organic framework (Co-MOF) nanotubes, which have a diameter of ∼70 nm and length of 20–35 μm with parallel multichannels (window size: 1.1 nm), have been successfully synthesized via an amorphous MOF-mediated recrystallization approach. The synthesized MOF nanotubes can be used as a nanocolumn for separation of large molecules. Carbonization of the Co-MOF nanotubes in an argon atmosphere preserves the 1D morphology, affording long carbon nanofibers. A hierarchical architecture composed of carbon nanofibers wrapped by carbon nanotubes (20–30 nm in diameter and 200–300 nm in length) with cobalt nanoparticles on the top is formed by the carbonization of the Co-MOF nanotubes along with dicyandiamide as a nitrogen and a secondary carbon source. The resulting hierarchical dendrites with carbon nanofiber trunks and carbon nanotube branches exhibit excellent electrocatalytic activity for oxygen reduction reaction and exceptional applications in rechargeable Zn–air batteries. This work demonstrates a new strategy to fabricate MOF nanotubes and relative 1D nanostructures.