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.
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.