title: Ion-Gated Gas Separation through Porous Graphene.
abstract: Porous graphene holds great promise as a one-atom-thin, high-permeance membrane for gas separation, but to precisely control the pore size down to 3-5 Å proves challenging. Here we propose an ion-gated graphene membrane comprising a monolayer of ionic liquid-coated porous graphene to dynamically modulate the pore size to achieve selective gas separation. This approach enables the otherwise nonselective large pores on the order of 1 nm in size to be selective for gases whose diameters range from 3 to 4 Å. We show from molecular dynamics simulations that CO2, N2, and CH4all can permeate through a 6 Å nanopore in graphene without any selectivity. But when a monolayer of [emim][BF4] ionic liquid (IL) is deposited on the porous graphene, CO2has much higher permeance than the other two gases. We find that the anion dynamically modulates the pore size by hovering above the pore and provides affinity for CO2, while the larger cation (which cannot go through the pore) holds the anion in place via electrostatic attraction. This composite membrane is especially promising for CO2/CH4separation, yielding a CO2/CH4selectivity of about 42 and CO2permeance of ∼105GPU (gas permeation unit). We further demonstrate that selectivity and permeance can be tuned by the anion size, pore size, and IL thickness. The present work points toward a promising direction of using the atom-thin ionic liquid/porous graphene hybrid membrane for high-permeance, selective gas separation that allows a greater flexibility in substrate pore size control.
authors.affiliation: Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: Ziqi
authors.initials: Z
authors.lastname: Tian
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.
authors.forename: Shannon M
authors.initials: SM
authors.lastname: Mahurin
authors.affiliation: Chemical Sciences Division, Oak Ridge National Laboratory , Oak Ridge, Tennessee 37831, United States.|Department of Chemistry, The University of Tennessee , Knoxville, Tennessee 37996, United States.
authors.forename: Sheng
authors.identifier: 0000-0002-8046-3931
authors.initials: S
authors.lastname: Dai
authors.affiliation: Department of Chemistry, University of California , Riverside, California 92521, United States.
authors.forename: De-En
authors.identifier: 0000-0001-5167-0731
authors.initials: DE
authors.lastname: Jiang
keywords: Porous graphene; gas separation; ionic liquid; membrane; molecular dynamics