Controlled synthesis of highly stable zeolitic imidazolate framework-67 dodecahedra and their use towards the templated formation of a hollow Co3O4 catalyst for CO oxidation

Abstract

In this work, dodecahedral microcrystals of zeolitic imidazolate framework-67 (ZIF-67) with good uniformity and exceptional stability have been synthesized by simply controlling the mole ratio of reactants at room temperature. Field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) characterization indicates that the as-synthesized ZIF-67 microcrystals are highly uniform and have perfect rhombic dodecahedral morphology with 12 exposed {110} faces. The X-ray diffraction (XRD) and thermogravimetry analysis (TGA) investigations demonstrate that they display high thermal stability up to ∼350 °C in air and ∼425 °C in vacuum, as well as remarkable chemical resistance to boiling organic solvents and room-temperature water. Through a two-step oxidative thermolysis process, these ZIF-67 dodecahedra can be further converted into hollow Co₃O₄ architectures consisting of nanosized building blocks. Owing to their large specific surface area and unique structure, the hollow Co₃O₄ catalyst obtained at the calcination temperature of 425 °C exhibits high catalytic activity and stability for gas-phase CO oxidation.