Microstructural study of the formation mechanism of metal–organic framework MOF-5

Abstract

Metal–organic framework, MOF-5, is re-synthesised using an established method, which reveals an extraordinary formation mechanism. The earliest detected crystalline phase is Zn₅(OH)₈(NO₃)₂·2H₂O, in the form of nanoplatelets 5 to 10 nm in diameter, which aggregate with surface adsorbed organic molecules into a layered inorganic–organic composite. Multiple nucleation of MOF-5 takes place inside the composite via intercalation of 1,4-benzenedicarboxylate molecules and phase transformation from Zn₅(OH)₈(NO₃)₂·2H₂O. The as-formed MOF-5 nanocrystallites aggregate into cubic polycrystalline particles, which undergo surface re-crystallisation followed by extension of re-crystallisation from the surface to the core. This newly established formation mechanism may shed light on the crystal growth of many other MOFs. It may enable scientists to precisely control the microstructures and morphologies of these materials and gain a better understanding of their properties for future applications.