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

Abstract

Mesoporous materials | Metal-organic frameworks | Cycloaddition | Steam etching | Dye removalThe 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 CO 2 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.

Recent Advances in Hierarchical Porous Engineering of MOFs and Their Derived Materials for Catalytic and Battery: Methods and Application

“…Therefore, phosphoric acid molecules only diffuse into specific channels, and selectively etch MOFs After heating, the phosphoric acid can etch the MIL‐100 structure selectively to form mesoporous structure (Figure 10b). [ 66 ] Additionally, research on etching MOFs by plasma, [ 70 ] ions, [ 67 ] hot steam, [ 69 ] and reducing vapor ozone [ 68 ] has also reported to introduce mesoporous defects to MOFs (Figure 10c–e).…”

“…e) Schematic illustration of the hierarchical porous ZIF-8 fabricated by air-steam etching. Reproduced with permission [69]. Copyright 2021, Wiley-VCH.…”

Water-Etched Approach to Hierarchically Porous Metal–Organic Frameworks with High Stability

“…Chemical etching and template methods are often used to construct defective HP-MOFs. For these approaches, the strong acid and base are often adopted in etching processes or to remove the templates, and MOFs often lose crystallinity during this process, which cannot meet the requirements of further applications. − Therefore, the development of green and mild approaches to construct defective HP-MOFs with high stability is highly desired, but remains challenging to date.…”

Boosting CO2 chemical fixation over MOF-808 by the introduction of functional groups and defective Zr sites

“…7 Though the modification of organic linkers and metal cores both lead to largely improved activity of ZIF-based catalysts, these catalysts suffer from inferior stability due to the destruction of weak metal-N bonds (bond energy of 119 kJ mol À1 ) during the reaction. 7,8 In contrast, metal-O-based MOFs exhibit excellent stability due to much stronger metal-O bonds. 9 For instance, defect-rich UiO-66, prepared by plasma etching, has demonstrated remarkable stability in CO 2 cycloaddition.…”

“…7 Though the modification of organic linkers and metal cores both lead to largely improved activity of ZIF-based catalysts, these catalysts suffer from inferior stability due to the destruction of weak metal–N bonds (bond energy of 119 kJ mol −1 ) during the reaction. 7,8…”