Morphology Engineering of Metal-Organic Frameworks by Facet-Selective Protection and Etching

Anisotropic etching is a novel and effective means to modulate facets of metal-organic frameworks (MOFs) which deserves continuous exploration. Herein, we developed a facet-selective protection and etching method to achieve morphology control of MOFs. Our approach exploits the compositional differences between the facets of zeolitic imidazolate framework-67 and the moderate coordinating and etching properties of ethylenediaminetetraacetic acid disodium salt (EdtaH₂Na₂). The selected chelator, EdtaH₂^2-, can specifically coordinate with unsaturated metal sites on the {100} crystal planes, protecting them from proton etching and meanwhile releasing protons. Moreover, the released protons with locally high concentration led to the etching of the unprotected {110} facets, ultimately forming nanocrystals with selectively exposed surfaces. This anisotropic etching strategy facilitates the precise modification of MOF surfaces, which is anticipated to play a crucial role in enhancing their properties in different application areas.