Pressure‐Responsive Two‐Dimensional Metal–Organic Framework Composite Membranes for CO₂ Separation

Abstract

The regulation of permeance and selectivity in membrane systems may allow effective relief of conventional energy-intensive separations.H ere,p ressure-responsive ultrathin membranes ( % 100 nm) fabricated by compositing flexible two-dimensional metal-organic framework nanosheets (MONs) with graphene oxide nanosheets for CO 2 separation are reported. By controlling the gas permeation direction to leverage the pressure-responsive phase transition of the MONs, CO 2 -induced gate opening and closing behaviors are observed in the resultant membranes,w hich are accompanied with the sharp increase of CO 2 permeance (from 173.8 to 1144 gas permeation units) as well as CO 2 /N 2 and CO 2 /CH 4 selectivities (from 4.1 to 22.8 and from 4to19.6, respectively). The flexible behaviors and separation mechanism are further elucidated by molecular dynamics simulations.T his work establishes the relevance of structural transformation-based framework dynamics chemistry in smart membrane systems.

Smart Two‐Dimensional Membranes for Molecular Separations

“…To date, GO has been reported in molecular separation applications such as being filled with ionic liquid for smart features in an electric field, [27] in a device with metal electrodes to show conductive features in a controlled electric field (Figure 2a), [28] and as a director of gas permeation to leverage the phase transition of MOFs in response to pressure. [23] Recently, Guo et al [29] generated spatial confinement on GO assembling by molecular intercalations, and the structures of sieving channels are regulated. Consequently, intercalation with optimal-sized molecules creates an ultrafast water permeance that is 5 times more than pristine GO membrane.…”

“…Examples of smart 2D MOFs for molecular separation include the molecular flexibility of metal-organic nanosheets (through their tert-butyl groups) in response to temperature (Figure 2c), [24d] the in-plane microporous substrate for housing ionic liquid in response to light, [31] and the gate flexibility when a few layers of 2D MOF nanosheets are confined between GO nanosheets and subjected to different pressures. [23] With their structural diversity, more novel smart 2D MOFs can be prepared in future works.…”

“…At present, pressure-assisted self-assembly (PASA) filtration, [23] vacuum-assisted self-assembly (VASA) filtration, [24a] and drop-casting [24d] are the common top-down methods for fabricating smart 2D membranes. The filtration-assisted assembly methods can efficiently adjust the thickness of the membrane by changing the deposition quantities from submicrometer to nanometer, while the casting technique is able to produce homogeneous membranes with scale-up potential.…”

“…Given their tunability, high permeance and high selectivity, molecular separations through smart 2D membranes are a growing area of research. [23] Herein, we highlight the application of smart 2D membranes in molecular separations. As smart 2D membranes are relatively new, their molecular separation applications are in their infancy.…”

Th-MOF showing six-fold imide-sealed pockets for middle-size-separation of propane from nature gas

“…The size and con guration of pore in MOFs presents a highly important factor for separation [25][26][27][28][29] . MOFs could selective adsorption of gas molecules with smaller size than the pore MOFs, but will exclude these gas molecules with bigger size than the pore MOFs 30,31 .…”