The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Taishung Chung - One of the best experts on this subject based on the ideXlab platform.

  • a novel crosslinking technique towards the fabrication of high flux polybenzimidazole pbi membranes for organic solvent nanofiltration osn
    Separation and Purification Technology, 2019
    Co-Authors: Mohammad Hossein Davood Abadi Farahani, Taishung Chung
    Abstract:

    Abstract A green crosslinking method has been proposed to design high-flux polybenzimidazole (PBI) membranes for organic solvent nanofiltration (OSN). Integrally skinned asymmetric PBI membranes were crosslinked using a solution containing trimesoyl chloride (TMC) and environmentally benign 2-methyl tetrahydrofuran (2-MeTHF) for the first time. The separation performance of the crosslinked PBI (X-PBI) membranes towards various solutes and solvents, including polar and nonpolar solvents, have been carefully studied. The X-PBI membrane shows a rejection of 99.6% to remazol brilliant blue R (MW of 627 g/mol) while it has pure acetonitrile, acetone, ethanol, and isopropanol Permeances of 40.7, 29.0, 13.8, and 5.8 LMH/bar at 10 bar, respectively. Moreover, the X-PBI membrane exhibits superlative performance during the 2-step filtration of tetracycline, an antibiotic compound with a MW of 444 g/mol. It has rejections of 90.4% and 97.8% in the first and second steps of filtration, respectively. The X-PBI membrane is also able to concentrate solutions containing L-α-lecithin, a food additive with a MW of 758 g/mol, from hexane. It has a L-α-lecithin rejection of 92% and a pure hexane Permeance of 80.8 LMH/bar at 10 bar. Besides, it shows great potential to separate mixed dyes and stable OSN performance during 96-h continuous tests.

  • high performance multiple layer pim composite hollow fiber membranes for gas separation
    Journal of Membrane Science, 2018
    Co-Authors: Can Zeng Liang, Jiangtao Liu, Juinyih Lai, Taishung Chung
    Abstract:

    Abstract The invention of polymers of intrinsic microporosity (PIMs) has opened up great opportunities for the developments of high-performance composite membranes which possess both high gas Permeance and selectivity. However, it still remains challenging to translate such PIM materials into PIM-related composite membranes with characteristics of high Permeance and selectivity. For the first time, we report defect-free PIM composite hollow fiber membranes that have pure O2 and CO2 Permeances of 69 and 483 GPU, respectively, and O2/N2 and CO2/N2 selectivities of 3.2 and 22.5, respectively. The O2/N2 and CO2/N2 selectivities are further increased to 4.2 and 29.5 respectively in air separation and flue gas tests. The composite hollow fiber membranes consist of three layers. The top selective-layer material is made from the nucleophilic substitution copolymerization between PIM and beta-cyclodextrin (β-CD) (referred to as PIM-CD), while the gutter and substrate materials are polydimethylsiloxane (PDMS) and polyacrylonitrile (PAN), respectively. The key to producing such composite membranes is to introduce a cross-linked PDMS gutter layer between the PIM-CD selective layer and PAN substrates that can (1) mitigate the detrimental solvent effects during the dip coating, (2) allow PIM to adhere on it, and (3) redistribute the gas transport across the membranes.

  • performance enhancement in organic solvent nanofiltration by double crosslinking technique using sulfonated polyphenylsulfone sppsu and polybenzimidazole pbi
    Journal of Membrane Science, 2018
    Co-Authors: Akbar Asadi Tashvigh, Taishung Chung, Lin Luo, Martin Weber, Christian Maletzko
    Abstract:

    Abstract In this paper, we report a new technique to design highly stable and selective organic solvent nanofiltration (OSN) membranes with enhanced solvent Permeance by manipulating the crosslinking reactions. The new technique consists of three steps: (1) membrane fabrication via non-solvent induced phase inversion by blending sulfonated polyphenylsulfone (sPPSU) and polybenzimidazole (PBI) polymers, followed by (2) crosslinking the PBI part using α,α′-dibromo-p-xylene (DBX) to make the membrane chemically stable, and (3) ionically crosslinking the sPPSU part with hyperbranched polyethylenimine (HPEI) to narrow down the membrane pore size without affecting the Permeance significantly. Crosslinking reactions have been confirmed by FTIR and XPS analyses. The OSN performance of the double crosslinked membranes was determined by measuring the Permeance of various organic solvents and the rejection rates of tetracycline (Mw = 444 g mol−1) as a model pharmaceutical. Depending on the testing solvents, the Permeances ranged from 2 to 11.8 L m−2 h−1 bar−1, while the rejection rates of tetracycline varied from 67% to 97%. Considering the outstanding OSN performance and the great chemical stability in a wide range of solvent polarities, this novel double crosslinking technique represents a step forward in the fabrication of high performance OSN membranes.

  • Green Design of Poly(m‑Phenylene Isophthalamide)-Based Thin-Film Composite Membranes for Organic Solvent Nanofiltration and Concentrating Lecithin in Hexane
    2018
    Co-Authors: Dan Hua, Susilo Japip, Kai Yu Wang, Taishung Chung
    Abstract:

    A green method to fabricate poly­(m-phenylene isophthalamide) (PMIA) based thin-film composite membranes has been developed for organic solvent nanofiltration (OSN). For the first time, the porous PMIA membrane substrates are cast from dope solutions prepared by an environmentally benign ionic liquid and the thin-film selective layer is synthesized on top of the glutaraldehyde (GA) modified PMIA substrate (mPMIA) via imine condensation between hyper-branched polyethylenimine (HPEI) using water as the reaction media. Experimental results show that both HPEI and GA concentrations play important roles in controlling the thickness and free volume properties of the selective layer, and thus influence the OSN separation performance significantly. The newly designed composite membranes have an ethanol Permeance varying from 3.2 to 21.4 LMH/bar while the corresponding MWCO value changing from 470 to 730 Da when both HPEI and GA concentrations reduce from 1 to 0.5 wt %. In summary, the newly fabricated membranes not only possess satisfactory Permeances for solvents like methanol, ethanol, acetonitrile, and hexane but also have good separation performance for concentrating lecithin in hexane, which is in great demand by the food industry. Therefore, this work may offer a green and sustainable method to design environmentally benign composite membranes for OSN

  • cross linked mixed matrix membranes consisting of carboxyl functionalized multi walled carbon nanotubes and p84 polyimide for organic solvent nanofiltration osn
    Separation and Purification Technology, 2017
    Co-Authors: Mohammad Hossein Davood Abadi Farahani, Dan Hua, Taishung Chung
    Abstract:

    Abstract We have fabricated mixed matrix membranes (MMMs) consisting of carboxyl-functionalized multi-walled carbon nanotubes (MWCNTs-COOH) and P84 polyimide in this study for organic solvent nanofiltration (OSN) with the aid of chemical cross-linking by 1,6-hexanediamine (HDA). A moderate annealing is also used to manipulate the pore size for a better solute rejection. The incorporation of hydrophilic carbon nanotubes into P84 not only improves liquid sorption and transport but also increases membrane porosity and pore size. As a result, the Permeances of water, ethanol, and isopropanol across the MMMs increases with an increase in MWCNTs-COOH loading up to 0.075 wt.%. However, a higher loading of MWCNTs-COOH reduces the separation performance. The cross-linked MMM comprising 0.05 wt.% MWCNTs-COOH has a rejection of 85% to rose bengal (1017.65 Da) while ethanol Permeance is 9.6 LMH⋅bar −1 at 5 bar. Interestingly, the rejection of rose bengal in isopropanol solutions is higher than that in ethanol solutions (i.e., 99 vs. 85%). After thermal annealing at 150 °C in a 3/1 EG/PEG400 (weight ratio) solution, the resultant membranes (MMM comprising 0.05 wt.% MWCNTs-COOH) show superlative rejections to small dye molecules (almost 100% to Safranin O dye molecules, 350.85 Da) in ethanol solutions. There is an obvious trade-off between rejection and Permeance among the fabricated membranes, in which, the Permeance enhancement and rejection diminishing occurred with the addition of MWCNTs-COOH; however, a vice-versa trend was observed in annealed membranes.

Shigeharu Morooka - One of the best experts on this subject based on the ideXlab platform.

  • gas permeation properties of ion exchanged faujasite type zeolite membranes
    Aiche Journal, 1999
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, K Uchino, Yasuhisa Hasegawa, Shigeharu Morooka
    Abstract:

    NaY-type zeolite membranes were synthesized on a porous support tube by a hydrothermal process. The membranes were ion-exchanged with Li+ and K+ ions, and Permeances through the membranes were determined for an equimolar mixture of CO2 and N2, as well as for single-components thereof, at a temperature range of 0–400°C. The Permeance to CO2 showed a maximum at 100°C, but CO2/N2 selectivity decreased with increasing temperature. The zeolite membranes that were exchanged with K+ and Li+ ions gave higher and lower CO2/N2 selectivities, respectively, than were found for the NaY-type membrane. The permeation properties of the ion-exchanged zeolite membranes were analyzed using a sorption–diffusion model. The high CO2/N2 selectivity of the K-exchanged membranes can be explained by the decrease in N2 sorptivity for the mixed feed.

  • separation of carbon dioxide from nitrogen using ion exchanged faujasite type zeolite membranes formed on porous support tubes
    Journal of Membrane Science, 1998
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, Shigeharu Morooka
    Abstract:

    Abstract Faujasite-type zeolite membranes were reproducibly synthesized by hydrothermal reaction on the outer surface of a porous α -alumina support tube of 30 or 200 mm in length. The membrane properties were evaluated by CO 2 separation from an equimolar mixture of CO 2 and N 2 at a permeation temperature of 40°C. CO 2 Permeance and CO 2 /N 2 selectivity of the NaY-type membranes were in the ranges of 0.4×10 −6 –2.5×10 −6  mol m −2  s −1  Pa −1 and 20–50, respectively. The NaY-type membranes were ion-exchanged with alkali and alkaline earth cations. The LiY-type membrane showed the highest N 2 Permeance and the lowest CO 2 /N 2 selectivity. The KY-type membrane gave the highest CO 2 /N 2 selectivity. The NaY-type membrane was stable against exposure to air at 400°C. NaX-type zeolite membranes, formed by decreasing the ratio of SiO 2 /Al 2 O 3 in the starting solution, exhibited lower CO 2 Permeances and higher CO 2 /N 2 selectivities than those of the NaY-type zeolite membranes.

  • pore size control and gas permeation kinetics of silica membranes by pyrolysis of phenyl substituted ethoxysilanes with cross flow through a porous support wall
    Journal of Membrane Science, 1997
    Co-Authors: Katsuki Kusakabe, Shigeharu Morooka
    Abstract:

    Abstract A silica membrane was produced by chemical vapor deposition using tetraethoxysilane (TEOS), phenyltriethoxysilane (PTES) or diphenyldiethoxysilane (DPDES) as the Si source. Amorphous silica was deposited in the mesopores of a γ-alumina film coated on a porous α-alumina tube, by evacuating the reactant through the porous wall. Hydrogen Permeance at a permeation temperature of 600°C was of the order of 10−7 mol m−2 s−1 Pa−1, and was not greatly dependent on the Si sources. The silica membrane produced using TEOS contained micropores permeable to both helium and hydrogen, but CO2 and larger molecules were only slightly permeated through those mesopores which were left unplugged. The silica membrane produced from DPDES showed a single-component CO2 Permeance equivalent to that of single-component He, and CO 2 N 2 selectivity was approximately 9 at a permeation temperature of 30°C. When a mixture of CO2 and N2 was fed, however, CO2 Permeance decreased to the level of N2 Permeance. The H 2 N 2 selectivity, determined from single-component Permeances to H2 and N2, was approximately 100, and these Permeances remained unchanged when an equimolar mixture of H2 and N2 was fed. Thus, the DPDES-derived membrane possessed two types of micropores, abundant pores through which helium and hydrogen permeated and a small number of pores in which molecules of CO2 and N2 were permeable but not able to pass one another. Neither meso or macropores remained in the DPDES membrane.

  • formation of a y type zeolite membrane on a porous α alumina tube for gas separation
    Industrial & Engineering Chemistry Research, 1997
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, And Atsushi Murata, Shigeharu Morooka
    Abstract:

    A porous α-alumina support tube, polished with a finely powdered X-type zeolite for use as seeds, was placed vertically in an autoclave containing an aqueous mixture of water glass and sodium aluminate. Hydrothermal synthesis was carried out at 90 °C for 24 h. A polycrystalline layer of Y-type zeolite was thus formed on the outer surface of the support tube. After washing and drying in air, Permeances of single components and mixtures of CO2 and N2, as well as CH4, C2H6, and SF6, were determined. The CO2 Permeance was higher than that of N2 at temperatures of 30−130 °C. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 Permeance was nearly equal to that for the single-component system and the N2 Permeance for the mixture was greatly decreased, especially at lower permeation temperatures. This was due to selective adsorption of CO2 in subnanometer micropores of the membrane. At 30 °C, the Permeance of CO2 was higher than 10-7 mol·m-2·s-1·Pa-1, and the permselectivity of CO2 to N2 ...

Katsuki Kusakabe - One of the best experts on this subject based on the ideXlab platform.

  • gas permeation properties of ion exchanged faujasite type zeolite membranes
    Aiche Journal, 1999
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, K Uchino, Yasuhisa Hasegawa, Shigeharu Morooka
    Abstract:

    NaY-type zeolite membranes were synthesized on a porous support tube by a hydrothermal process. The membranes were ion-exchanged with Li+ and K+ ions, and Permeances through the membranes were determined for an equimolar mixture of CO2 and N2, as well as for single-components thereof, at a temperature range of 0–400°C. The Permeance to CO2 showed a maximum at 100°C, but CO2/N2 selectivity decreased with increasing temperature. The zeolite membranes that were exchanged with K+ and Li+ ions gave higher and lower CO2/N2 selectivities, respectively, than were found for the NaY-type membrane. The permeation properties of the ion-exchanged zeolite membranes were analyzed using a sorption–diffusion model. The high CO2/N2 selectivity of the K-exchanged membranes can be explained by the decrease in N2 sorptivity for the mixed feed.

  • separation of carbon dioxide from nitrogen using ion exchanged faujasite type zeolite membranes formed on porous support tubes
    Journal of Membrane Science, 1998
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, Shigeharu Morooka
    Abstract:

    Abstract Faujasite-type zeolite membranes were reproducibly synthesized by hydrothermal reaction on the outer surface of a porous α -alumina support tube of 30 or 200 mm in length. The membrane properties were evaluated by CO 2 separation from an equimolar mixture of CO 2 and N 2 at a permeation temperature of 40°C. CO 2 Permeance and CO 2 /N 2 selectivity of the NaY-type membranes were in the ranges of 0.4×10 −6 –2.5×10 −6  mol m −2  s −1  Pa −1 and 20–50, respectively. The NaY-type membranes were ion-exchanged with alkali and alkaline earth cations. The LiY-type membrane showed the highest N 2 Permeance and the lowest CO 2 /N 2 selectivity. The KY-type membrane gave the highest CO 2 /N 2 selectivity. The NaY-type membrane was stable against exposure to air at 400°C. NaX-type zeolite membranes, formed by decreasing the ratio of SiO 2 /Al 2 O 3 in the starting solution, exhibited lower CO 2 Permeances and higher CO 2 /N 2 selectivities than those of the NaY-type zeolite membranes.

  • pore size control and gas permeation kinetics of silica membranes by pyrolysis of phenyl substituted ethoxysilanes with cross flow through a porous support wall
    Journal of Membrane Science, 1997
    Co-Authors: Katsuki Kusakabe, Shigeharu Morooka
    Abstract:

    Abstract A silica membrane was produced by chemical vapor deposition using tetraethoxysilane (TEOS), phenyltriethoxysilane (PTES) or diphenyldiethoxysilane (DPDES) as the Si source. Amorphous silica was deposited in the mesopores of a γ-alumina film coated on a porous α-alumina tube, by evacuating the reactant through the porous wall. Hydrogen Permeance at a permeation temperature of 600°C was of the order of 10−7 mol m−2 s−1 Pa−1, and was not greatly dependent on the Si sources. The silica membrane produced using TEOS contained micropores permeable to both helium and hydrogen, but CO2 and larger molecules were only slightly permeated through those mesopores which were left unplugged. The silica membrane produced from DPDES showed a single-component CO2 Permeance equivalent to that of single-component He, and CO 2 N 2 selectivity was approximately 9 at a permeation temperature of 30°C. When a mixture of CO2 and N2 was fed, however, CO2 Permeance decreased to the level of N2 Permeance. The H 2 N 2 selectivity, determined from single-component Permeances to H2 and N2, was approximately 100, and these Permeances remained unchanged when an equimolar mixture of H2 and N2 was fed. Thus, the DPDES-derived membrane possessed two types of micropores, abundant pores through which helium and hydrogen permeated and a small number of pores in which molecules of CO2 and N2 were permeable but not able to pass one another. Neither meso or macropores remained in the DPDES membrane.

  • formation of a y type zeolite membrane on a porous α alumina tube for gas separation
    Industrial & Engineering Chemistry Research, 1997
    Co-Authors: Katsuki Kusakabe, Takahiro Kuroda, And Atsushi Murata, Shigeharu Morooka
    Abstract:

    A porous α-alumina support tube, polished with a finely powdered X-type zeolite for use as seeds, was placed vertically in an autoclave containing an aqueous mixture of water glass and sodium aluminate. Hydrothermal synthesis was carried out at 90 °C for 24 h. A polycrystalline layer of Y-type zeolite was thus formed on the outer surface of the support tube. After washing and drying in air, Permeances of single components and mixtures of CO2 and N2, as well as CH4, C2H6, and SF6, were determined. The CO2 Permeance was higher than that of N2 at temperatures of 30−130 °C. When an equimolar mixture of CO2 and N2 was fed into the feed side, the CO2 Permeance was nearly equal to that for the single-component system and the N2 Permeance for the mixture was greatly decreased, especially at lower permeation temperatures. This was due to selective adsorption of CO2 in subnanometer micropores of the membrane. At 30 °C, the Permeance of CO2 was higher than 10-7 mol·m-2·s-1·Pa-1, and the permselectivity of CO2 to N2 ...

Michael S Strano - One of the best experts on this subject based on the ideXlab platform.

  • predicting gas separation through graphene nanopore ensembles with realistic pore size distributions
    ACS Nano, 2021
    Co-Authors: Zhe Yuan, Michael S Strano, Ananth Govind Rajan, Rahul Prasanna Misra, Daniel Blankschtein
    Abstract:

    The development of nanoporous single-layer graphene membranes for gas separation has prompted increasing theoretical investigations of gas transport through graphene nanopores. However, computer simulations and theories that predict gas Permeances through individual graphene nanopores are not suitable to describe experimental results, because a realistic graphene membrane contains a large number of nanopores of diverse sizes and shapes. With this need in mind, here, we generate nanopore ensembles in silico by etching carbon atoms away from pristine graphene with different etching times, using a kinetic Monte Carlo algorithm developed by our group for the isomer cataloging problem of graphene nanopores. The Permeances of H2, CO2, and CH4 through each nanopore in the ensembles are predicted using transition state theory based on classical all-atomistic force fields. Our findings show that the total gas Permeance through a nanopore ensemble is dominated by a small fraction of large nanopores with low energy barriers of pore crossing. We also quantitatively predict the increase of the gas Permeances and the decrease of the selectivities between the gases as functions of the etching time of graphene. Furthermore, by fitting the theoretically predicted selectivities to the experimental ones reported in the literature, we show that nanopores in graphene effectively expand as the temperature of permeation measurement increases. We propose that this nanopore "expansion" is due to the desorption of contaminants that partially clog the graphene nanopores. In general, our study highlights the effects of the pore size and shape distributions of a graphene nanopore ensemble on its gas separation properties and calls into attention the potential effect of pore-clogging contamination in experiments.

  • stable temperature dependent gas mixture permeation and separation through suspended nanoporous single layer graphene membranes
    Nano Letters, 2018
    Co-Authors: Zhe Yuan, Jesse D Benck, Yannick Eatmon, Daniel Blankschtein, Michael S Strano
    Abstract:

    Graphene membranes with nanometer-scale pores could exhibit an extremely high Permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent Permeance of gas mixtures in an equimolar mixture feed containing H2, He, CH4, CO2, and SF6 from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeable Ni. Two membranes exhibited gas Permeances on the order of 10–6 to 10–5 mol m–2 s–1 Pa–1 as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the Permeance data and selectivities. This mechanism predicts a mean p...

  • Stable, Temperature-Dependent Gas Mixture Permeation and Separation through Suspended Nanoporous Single-Layer Graphene Membranes
    2018
    Co-Authors: Zhe Yuan, Jesse D Benck, Yannick Eatmon, Daniel Blankschtein, Michael S Strano
    Abstract:

    Graphene membranes with nanometer-scale pores could exhibit an extremely high Permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent Permeance of gas mixtures in an equimolar mixture feed containing H2, He, CH4, CO2, and SF6 from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeable Ni. Two membranes exhibited gas Permeances on the order of 10–6 to 10–5 mol m–2 s–1 Pa–1 as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the Permeance data and selectivities. This mechanism predicts a mean pore diameter of 2.5 nm and an areal pore density of 7.3 × 1013 m–2, which is validated by experimental observations. A third membrane exhibited selectivities lower than the Knudsen effusion selectivities, suggesting a combination of effusion and viscous flow. A fourth membrane exhibited increasing Permeance values as functions of temperature from 27 to 200 °C, and a CO2/SF6 selectivity > 20 at 200 °C, suggestive of activated translocation through molecular-sized nanopores. A fifth membrane exhibited no measurable Permeance of any gas above the detection limit of our technique, 2 × 10–7 mol m–2 s–1 Pa–1, indicating essentially a molecularly impermeable barrier. Overall, these data demonstrate that SLG membranes can potentially provide a high mixture separation selectivity for gases, with CVD synthesis alone resulting in nanometer-scale pores useful for gas separation. This work also shows that temperature-dependent Permeance measurements on SLG can be used to reveal underlying permeation mechanisms

Zhe Yuan - One of the best experts on this subject based on the ideXlab platform.

  • predicting gas separation through graphene nanopore ensembles with realistic pore size distributions
    ACS Nano, 2021
    Co-Authors: Zhe Yuan, Michael S Strano, Ananth Govind Rajan, Rahul Prasanna Misra, Daniel Blankschtein
    Abstract:

    The development of nanoporous single-layer graphene membranes for gas separation has prompted increasing theoretical investigations of gas transport through graphene nanopores. However, computer simulations and theories that predict gas Permeances through individual graphene nanopores are not suitable to describe experimental results, because a realistic graphene membrane contains a large number of nanopores of diverse sizes and shapes. With this need in mind, here, we generate nanopore ensembles in silico by etching carbon atoms away from pristine graphene with different etching times, using a kinetic Monte Carlo algorithm developed by our group for the isomer cataloging problem of graphene nanopores. The Permeances of H2, CO2, and CH4 through each nanopore in the ensembles are predicted using transition state theory based on classical all-atomistic force fields. Our findings show that the total gas Permeance through a nanopore ensemble is dominated by a small fraction of large nanopores with low energy barriers of pore crossing. We also quantitatively predict the increase of the gas Permeances and the decrease of the selectivities between the gases as functions of the etching time of graphene. Furthermore, by fitting the theoretically predicted selectivities to the experimental ones reported in the literature, we show that nanopores in graphene effectively expand as the temperature of permeation measurement increases. We propose that this nanopore "expansion" is due to the desorption of contaminants that partially clog the graphene nanopores. In general, our study highlights the effects of the pore size and shape distributions of a graphene nanopore ensemble on its gas separation properties and calls into attention the potential effect of pore-clogging contamination in experiments.

  • stable temperature dependent gas mixture permeation and separation through suspended nanoporous single layer graphene membranes
    Nano Letters, 2018
    Co-Authors: Zhe Yuan, Jesse D Benck, Yannick Eatmon, Daniel Blankschtein, Michael S Strano
    Abstract:

    Graphene membranes with nanometer-scale pores could exhibit an extremely high Permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent Permeance of gas mixtures in an equimolar mixture feed containing H2, He, CH4, CO2, and SF6 from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeable Ni. Two membranes exhibited gas Permeances on the order of 10–6 to 10–5 mol m–2 s–1 Pa–1 as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the Permeance data and selectivities. This mechanism predicts a mean p...

  • Stable, Temperature-Dependent Gas Mixture Permeation and Separation through Suspended Nanoporous Single-Layer Graphene Membranes
    2018
    Co-Authors: Zhe Yuan, Jesse D Benck, Yannick Eatmon, Daniel Blankschtein, Michael S Strano
    Abstract:

    Graphene membranes with nanometer-scale pores could exhibit an extremely high Permeance and selectivity for the separation of gas mixtures. However, to date, no experimental measurements of gas mixture separation through nanoporous single-layer graphene (SLG) membranes have been reported. Herein, we report the first measurements of the temperature-dependent Permeance of gas mixtures in an equimolar mixture feed containing H2, He, CH4, CO2, and SF6 from 22 to 208 °C through SLG membranes containing nanopores formed spontaneously during graphene synthesis. Five membranes were fabricated by transfer of CVD graphene from catalytic Cu film onto channels framed in impermeable Ni. Two membranes exhibited gas Permeances on the order of 10–6 to 10–5 mol m–2 s–1 Pa–1 as well as gas mixture selectivities higher than the Knudsen effusion selectivities predicted by the gas effusion mechanism. We show that a new steric selectivity mechanism explains the Permeance data and selectivities. This mechanism predicts a mean pore diameter of 2.5 nm and an areal pore density of 7.3 × 1013 m–2, which is validated by experimental observations. A third membrane exhibited selectivities lower than the Knudsen effusion selectivities, suggesting a combination of effusion and viscous flow. A fourth membrane exhibited increasing Permeance values as functions of temperature from 27 to 200 °C, and a CO2/SF6 selectivity > 20 at 200 °C, suggestive of activated translocation through molecular-sized nanopores. A fifth membrane exhibited no measurable Permeance of any gas above the detection limit of our technique, 2 × 10–7 mol m–2 s–1 Pa–1, indicating essentially a molecularly impermeable barrier. Overall, these data demonstrate that SLG membranes can potentially provide a high mixture separation selectivity for gases, with CVD synthesis alone resulting in nanometer-scale pores useful for gas separation. This work also shows that temperature-dependent Permeance measurements on SLG can be used to reveal underlying permeation mechanisms