During the last decade, the synthesis and application of metal-organic framework (MOF) nanosheets has received growing interest, showing unique performances for different technological applications. Despite the advances reported, the applicability of the synthetic methods developed so far is mainly restricted to MOFs possessing a layered structure. These MOFs consist of stacked 2D layers, being more prone to the formation of nanosheets. However, this subfamily of compounds only embodies a small fraction of the MOF structures reported to date, severely limiting the potential of this promising type of 2D nanomaterials. To the best of our knowledge, only one very recent example has been reported so far on the top-down exfoliation of 3D MOFs. However, top-down approaches are often associated with particle fragmentation and re-aggregation of the detached sheets. A bottom-up approach for the synthesis of 3D MOF has never been reported.
Within this context, we present a bottom-up surfactant-assisted synthetic approach for the fabrication of free-standing nanosheets of various non-layered 3D Al-containing MOFs, broadening the scope of MOF nanosheets application. Surfactant-assisted pre-organization of the metallic precursor prior to MOF synthesis allows for the manufacture of non-layered Al-containing MOF lamellae. These MOF nanosheets are shown to exhibit a superior performance over other crystal morphologies for both chemical sensing and gas separation. Gas separation behaviour of MOF nanosheets embedded in polymer matrix was explored for CO2/CH4 mixture and compared to the nanoparticle-containing composite. The NH2-MIL-53(Al) nanolamellae/Matrimid® mixed matrix membrane showed a 10-fold increase in CO2 permeability along with a doubled selectivity in the separation of CO2/CH4 mixtures. Moreover, sensing studies on NH2-MIL-53(Al) nanolamellae-coated device suggested the enhanced sensing performance towards different types of alcohols. As revealed by electron microscopy and diffraction, this superior performance arises from the shorter diffusion pathway in MOF nanosheets, whose one-dimensional channels are oriented along the shortest particle dimension.