Pressure-Responsive Two-Dimensional Metal-Organic Framework Composite Membranes for CO2 Separation.

The regulation of permeance and selectivity in membrane systems may allow effective relief of conventional energy-intensive separations. Here, pressure-responsive ultrathin membranes (≈100 nm) fabricated by compositing flexible two-dimensional metal-organic framework nanosheets (MONs) with graphene oxide nanosheets for CO2 separation are reported. By controlling the gas permeation direction to leverage the pressure-responsive phase transition of the MONs, CO2 -induced gate opening and closing behaviors are observed in the resultant membranes, which are accompanied with the sharp increase of CO2 permeance (from 173.8 to 1144 gas permeation units) as well as CO2 /N2 and CO2 /CH4 selectivities (from 4.1 to 22.8 and from 4 to 19.6, respectively). The flexible behaviors and separation mechanism are further elucidated by molecular dynamics simulations. This work establishes the relevance of structural transformation-based framework dynamics chemistry in smart membrane systems.