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Title: Ion-Gated Gas Separation through Porous Graphene

Abstract

Porous graphene holds great promise as an atom-thin, high-permeance membrane for gas separation, but to precisely control the pore size at three to five angstroms 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 non-selective large pores on the order of 1 nm in size to be selective for gases whose diameters range from three to four angstroms. We show from molecular dynamics simulations that CO 2, N 2 and CH 4 all can permeate through a 1-nm pore in graphene without any selectivity. But when a monolayer of [emim][BF 4] is deposited on the porous graphene, CO 2 has 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 CO 2 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 CO 2/CH 4 separation, with a CO 2/CH 4 selectivity of about 42 and CO 2 permeance ~105 GPU (gas permeationmore » unit). We further demonstrate that selectivity and permeance can be tuned by the anion size. 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.« less

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [1]
  1. Univ. of California, Riverside, CA (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1348344
Grant/Contract Number:
AC05-00OR22725
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Nano Letters
Additional Journal Information:
Journal Volume: 17; Journal Issue: 3; Journal ID: ISSN 1530-6984
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY

Citation Formats

Tian, Ziqi, Mahurin, Shannon M., Dai, Sheng, and Jiang, De-en. Ion-Gated Gas Separation through Porous Graphene. United States: N. p., 2017. Web. doi:10.1021/acs.nanolett.6b05121.
Tian, Ziqi, Mahurin, Shannon M., Dai, Sheng, & Jiang, De-en. Ion-Gated Gas Separation through Porous Graphene. United States. doi:10.1021/acs.nanolett.6b05121.
Tian, Ziqi, Mahurin, Shannon M., Dai, Sheng, and Jiang, De-en. Fri . "Ion-Gated Gas Separation through Porous Graphene". United States. doi:10.1021/acs.nanolett.6b05121. https://www.osti.gov/servlets/purl/1348344.
@article{osti_1348344,
title = {Ion-Gated Gas Separation through Porous Graphene},
author = {Tian, Ziqi and Mahurin, Shannon M. and Dai, Sheng and Jiang, De-en},
abstractNote = {Porous graphene holds great promise as an atom-thin, high-permeance membrane for gas separation, but to precisely control the pore size at three to five angstroms 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 non-selective large pores on the order of 1 nm in size to be selective for gases whose diameters range from three to four angstroms. We show from molecular dynamics simulations that CO2, N2 and CH4 all can permeate through a 1-nm pore in graphene without any selectivity. But when a monolayer of [emim][BF4] is deposited on the porous graphene, CO2 has 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/CH4 separation, with a CO2/CH4 selectivity of about 42 and CO2 permeance ~105 GPU (gas permeation unit). We further demonstrate that selectivity and permeance can be tuned by the anion size. 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.},
doi = {10.1021/acs.nanolett.6b05121},
journal = {Nano Letters},
number = 3,
volume = 17,
place = {United States},
year = {Fri Feb 10 00:00:00 EST 2017},
month = {Fri Feb 10 00:00:00 EST 2017}
}

Journal Article:
Free Publicly Available Full Text
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Cited by: 4works
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  • We investigate the permeability and selectivity of graphene sheets with designed subnanometer pores using first principles density functional theory calculations. We find high selectivity on the order of 10{sup 8} for H{sub 2}/CH{sub 4} with a high H{sub 2} permeance for a nitrogen-functionalized pore. We find extremely high selectivity on the order of 10{sup 23} for H{sub 2}/CH{sub 4} for an all-hydrogen passivated pore whose small width (at 2.5 {angstrom}) presents a formidable barrier (1.6 eV) for CH{sub 4} but easily surmountable for H{sub 2} (0.22 eV). These results suggest that these pores are far superior to traditional polymer andmore » silica membranes, where bulk solubility and diffusivity dominate the transport of gas molecules through the material. Recent experimental investigations, using either electron beams or bottom-up synthesis to create pores in graphene, suggest that it may be possible to employ such techniques to engineer variable-sized, graphene nanopores to tune selectivity and molecular diffusivity. Hence, we propose using porous graphene sheets as one-atom-thin, highly efficient, and highly selective membranes for gas separation. Such a pore could have widespread impact on numerous energy and technological applications; including carbon sequestration, fuel cells, and gas sensors.« less
  • By means of molecular dynamics (MD) simulations, we demonstrate that porous graphene can efficiently separate gases according to their molecular sizes. The flux sequence from the classical MD simulation is H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4}, which generally follows the trend in the kinetic diameters. This trend is also confirmed from the fluxes based on the computed free energy barriers for gas permeation using the umbrella sampling method and kinetic theory of gases. Both brute-force MD simulations and free-energy calcualtions lead to the flux trend consistent with experiments. Case studies of two compositions of CO{sub 2}/N{sub 2} mixtures further demonstrate themore » separation capability of nanoporous graphene. - Graphical abstract: Classical molecular dynamics simulations show the flux trend of H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4} for their permeation through a porous graphene, in excellent agreement with a recent experiment. - Highlights: • Classical MD simulations show the flux trend of H{sub 2}>CO{sub 2}≫N{sub 2}>Ar>CH{sub 4} for their permeation through a porous graphene. • Free energy calculations yield permeation barriers for those gases. • Selectivities for several gas pairs are estimated from the free-energy barriers and the kinetic theory of gases. • The selectivity trend is in excellent agreement with a recent experiment.« less
  • We demonstrate that porous graphene can efficiently separate gases according to their molecular sizes using molecular dynamic (MD) simulations,. The flux sequence from the classical MD simulation is H 2>CO 2>>N 2>Ar>CH 4, which generally follows the trend in the kinetic diameters. Moreover, this trend is also confirmed from the fluxes based on the computed free energy barriers for gas permeation using the umbrella sampling method and kinetic theory of gases. Both brute-force MD simulations and free-energy calcualtions lead to the flux trend consistent with experiments. Case studies of two compositions of CO 2/N 2 mixtures further demonstrate the separationmore » capability of nanoporous graphene.« less
  • Cited by 30
  • We calculate the surface response function and the image potential of a system of layered two-dimensional (2D) electron gas structures. A point charge is placed at a distance away from the surface which lies in the xy- plane. These 2D layers are coupled through the Coulomb interaction and there is no interlayer electron hopping. The separation between adjacent layers can be adjusted to investigate the roles which the layer separation and the number of layers play on both the surface response function and the image potential. Specifically, we consider the system composed of graphene layers or the layered 2D electronmore » gas (EG) formed at the interface of a semiconductor heterostructure such as GaAs/AlGaAs. We show that the image potential for graphene is qualitatively the same as for the 2DEG. We examine the way in which the image potential is modified by applying a one-dimensional periodic electrostatic potential (through a gated grating for modulation). The results indicate that the charge screening for graphene is not much different from the 2DEG.« less