Air‐Steam Etched Construction of Hierarchically Porous Metal‐Organic Frameworks

Main observation and conclusion The introduction of mesoporosity into the microporous metal‐organic frameworks (MOFs) is expected to expand their applications. Herein, we report a green and facile method to obtain hierarchically porous MOF structures by using an air‐steam etching process. By virtue of the protonation reaction between the imidazole moiety and water vapor, the protonated imidazole related linkers leave the framework, resulting in the formation of mesopores in the zeolitic imidazolate frameworks (ZIFs), as exemplified by ZIF‐8. Given the mild etching process, the materials’ structural integrity and crystallinity are well maintained. Accordingly, the hierarchical porous ZIF‐8 exhibited enhanced performance in the dye removal as well as CO2 cycloaddition reaction with epichlorohydrin in comparison with microporous ZIF‐8, owing to the accelerated mass transfer arising from mesoporous structures. Remarkably, the proposed steam etching approach is generally applicable, which can be readily extended to other ZIFs, such as ZIF‐14, ZIF‐69, and ZIF‐71, thus representing a powerful strategy to construct hierarchically porous MOF materials. A simple, scalable and green method was developed to prepare hierarchically porous MOFs via an air‐steam etching process without using any template or solvent. Water steam in air serves as an etching agent, which provides proton to linker, guaranteeing the feasibility of linker removal during etching process. This etching strategy not only can tune the mesopore structure of ZIF‐8 but also exhibits universal applicability to other ZIFs.