Two-Dimensional-Material Membranes: Manipulating the Transport Pathway for Molecular Separation

Abstract

Metrics & MoreArticle Recommendations * sı Supporting Information CONSPECTUS: The discovery of graphene triggers a new era of two-dimensional (2D) materials, which exhibit great potential in condensed matter physics, chemistry, and materials science. Meanwhile, the booming of 2D materials brings new opportunities for the next generation of high-performance (high permeability, selectivity, and stability) separation membranes. Two-dimensional materials with atomic thinness can serve as new building blocks for fabricating ultrathin membranes possessing the ultimate permeation rate. The plane structure with micrometer lateral dimensions provides an excellent platform for the orderly alignment of the nanosheets. Moreover, the apertures of two-dimensional-material membranes (2DMMs), including the in-plane nanopores and interlayer channels, can contribute to the fast and selective transport of small molecules/ions related to molecular separation. Therefore, the emerging 2D materials with various nanostructures, including graphene oxide (GO), zeolite nanosheets, metal− organic framework (MOF) nanosheets, and transition-metal carbides/carbonitrides (MXene), can be assembled into highperformance membranes. Various assembly methods such as filtration, spin coating, and hot dropping have been employed to fabricate 2DMMs, while the processes for separating small molecules/ions tend to demand higher precision, especially in water desalination and gas separation. The nanostructures of 2DMMs and the physicochemical properties of transport pathway need to be finely tuned to meet the requirement. In addition, the stability of 2DMMs, which is critical to the large-scale implementation, must be taken into consideration as well.In this Account, we discuss our recent progress in manipulating molecular transport pathways in 2DMMs by optimizing the assembly behavior of 2D nanosheets, tuning the microstructure of interlayer channels, and controlling the physicochemical properties of the membrane surface. Assembly methods, including vacuum suction assembly, polymer-induced assembly, and external force-driven assembly, have been proposed to construct ordered laminates for molecular transport. The size and chemical structure of interlayer channels were further tailored by strategies such as nanoparticle intercalation, cationic control, and chemical modification. Interestingly, the manipulation of surface properties of 2DMMs was proven to contribute to fast molecular transport through interlayer channels. Moreover, the issues concerning 2DMMs toward practical applications are discussed with an emphasis on the substrate effect, molecular bridge strategy, and preliminary progress in large-scale fabrication. Finally, we conclude this Account with an overview of the remaining challenges and the new opportunities that will be opened up for 2DMMs in molecular separation.

Advances in the Synthesis and Application of Anti-Fouling Membranes Using Two-Dimensional Nanomaterials

“…The diverse properties of 2DNMs offer vast opportunities for the development of 2DNMs-based membranes that can possess a large density of nanochannels spread across the material grain, high flux, exceptional salt rejection, and persistent antifouling capability [ 40 , 41 ]. The ultrathin nanosheets with integrated structures are necessary for manufacturing excellent performing 2DNM membranes.…”

“…The ultrathin nanosheets with integrated structures are necessary for manufacturing excellent performing 2DNM membranes. Generally, a top-down approach, which involves exfoliating the bulk layered crystals, and bottom-up approach, which involves direct production from the prime building units, are utilized to manufacture ultrathin 2DNM nanosheets [ 41 ]. Subsequently, the 2DNM nanosheets can be fabricated into continuous separation layers by using different approaches such as filtration, spin coating, hot dropping, etc.…”

“… ( A ) Graphic of two types of 2DNMs membrane: porous nanosheet membranes and laminar membranes (reproduced from [ 41 ] with permission from the American Chemical Society). ( B ) Fabrication of 2DNM membranes: ( a ) A schematic illustration of freestanding rGO membranes fabricated by vacuum-assisted method (reproduced from [ 44 ] with permission from the Wiley Online).…”

MIL‐101(Cr) Microporous Nanocrystals Intercalating Graphene Oxide Membrane for Efficient Hydrogen Purification

“…The manipulation of the microstructures and chemical properties of transport channels within GO laminates was proven to be critical to the gas separation performance of GO membranes [11] . In the previous work, we employed molecular interaction (e. g., hydrogen bonds) between GO and polymers or the integrated external forces to stimulate the ordered stacking of GO nanosheets and construct subnanometer channels for efficient gas sieving [12] .…”

“…[10] The manipulation of the microstructures and chemical properties of transport channels within GO laminates was proven to be critical to the gas separation performance of GO membranes. [11] In the previous work, we employed molecular interaction (e. g., hydrogen bonds) between GO and polymers or the integrated external forces to stimulate the ordered stacking of GO nanosheets and construct subnanometer channels for efficient gas sieving. [12] Jiang and co-workers introduced borate serving as crosslinker and facilitated transport carrier into GO laminates to tune the size of interlayer gallery and enhance the affinity of channels to CO 2 molecules, endowing the membrane with excellent CO 2 /CH 4 separation performance.…”