Reversed Crystal Growth of RHO Zeolitic Imidazolate Framework (ZIF)

RHO zeolitic imidazolate framework (ZIF), Zn1.33(O.OH)0.33(nim)1.167(pur), crystals with a rhombic dodecahedral morphology were synthesized by a solvothermal process. The growth of the crystals was studied over time using scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X‐ray diffraction (PXRD) and Brunauer–Emmett–Teller (BET) analyses, and a reversed crystal growth mechanism was revealed. Initially, precursor materials joined together to form disordered aggregates, which then underwent surface recrystallization forming a core–shell structure, in which a disordered core is encased in a layer of denser, less porous crystal. When the growth continued, the shell became less and less porous, until it was a layer of true single crystal. The crystallization then extended from the surface to the core over a six‐week period until, eventually, true single crystals were formed. Core–shell structures: Non‐classical reversed crystal growth of RHO ZIF with a rhombic dodecahedral morphology was revealed. The growth process includes aggregation of precursor materials to form disordered particles, surface re‐crystallization forming a core–shell structure, and extension of crystallisation from the shell to the core (see figure).