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.