Ultrathin metal/covalent–organic framework membranes towards ultimate separation

Abstract

Ultrathin metal/covalent–organic framework (MOF/COF) membranes have attracted increasing research interest and have been considered as state-of-the-art platforms applied in various environment- and energy-related separation/transportation processes.

Laminated self-standing covalent organic framework membrane with uniformly distributed subnanopores for ionic and molecular sieving

“…Based on abundant monomers, flexible bonding modes, and reversible covalent bonding, 2D COFs have the advantages of predesignable structure, tunable pore size, uniform pore distribution, and skeletal diversity [1][2][3][4][5] . These features make 2D COF a promising candidate for high quality membrane materials [6][7][8] . In addition, unlike other polymer and graphene membranes, additional physical or chemical methods will not be employed for creating pores or changing interlayer space in COF membrane preparation, and there is generally no need for postfunctionalization to adjust pore aperture, which actually simplifies the preparation process 9,10 .…”

“…used for COF synthesis mainly generate stacked or 3D bulk powders [11][12][13][14] . Despite some attempts have been made on free-standing or supported COF membranes, progress is very limited [6][7][8]15,16 . So researchers tried to fabricate COF membranes by vacuum filtration with the experience from preparation of graphene membranes.…”

“…Therefore, for the specific separation requirements, it is urgent to further narrow the pore sizes of the membranes to sub-nm scale. However, as far as size-dependent separation with COF membrane is concerned, it has been proved to be very difficult to accurately control the pore sizes in the sub-nm scale, either through control of monomer size or through pore modification [6][7][8] . Recently, Yang et al 35 reported several COF membranes with sub-nm pores prepared by vacuum filtration using 2D COF nanosheets and 1D cellulose nanofibers (CNFs) as starting materials.…”

Ultrathin permselective membranes: the latent way for efficient gas separation

“…Very recently, Zhang et al 44 have reviewed emerging inorganic materials such as MOFs and COFs in the preparation of ultrathin membranes using advanced strategies such as contradiffusion method, in situ growth, layer-by-layer (LBL) assembly, laminated assembly of MOF/COF nanosheets, metal-based precursor as the pre-functionalized layer, and interface-assisted strategy. To sum-up, the preparation of ultrathin membranes based on MOFs has been illustrated in Fig.…”

Two‐Dimensional MOF and COF Nanosheets: Synthesis and Applications in Electrochemistry

“…Recently, given that traditional bulk MOFs/COFs cannot fully meet the requirements of many special applications (especially in biological related applications, small‐size MOFs/COFs are needed to promote the internalization into cells), the preparation of MOF/COF nanocrystals with controllable size, shape and morphology has become a new challenge . Affected by the above research, a large number of studies on 2D MOFs/COFs have been published, mainly focusing on the exploration and optimization of the synthetic route . These unique properties and wide applications have stimulated the synthesis of 2D MOF/COF nanomaterials.…”