Morphology\nEngineering of Metal–Organic Frameworks\nby Facet-Selective Protection and Etching

Anisotropic etching is a novel and effective means to\nmodulate\nfacets of metal–organic frameworks (MOFs) which deserves continuous\nexploration. Herein, we developed a facet-selective protection and\netching method to achieve morphology control of MOFs. Our approach\nexploits the compositional differences between the facets of zeolitic\nimidazolate framework-67 and the moderate coordinating and etching\nproperties of ethylenediaminetetraacetic acid disodium salt (EdtaH<sub>2</sub>Na<sub>2</sub>). The selected chelator, EdtaH<sub>2</sub><sup>2–</sup>, can specifically coordinate with unsaturated metal\nsites on the {100} crystal planes, protecting them from proton etching\nand meanwhile releasing protons. Moreover, the released protons with\nlocally high concentration led to the etching of the unprotected {110}\nfacets, ultimately forming nanocrystals with selectively exposed surfaces.\nThis anisotropic etching strategy facilitates the precise modification\nof MOF surfaces, which is anticipated to play a crucial role in enhancing\ntheir properties in different application areas.