Periodic Reporting for period 1 - CNSOL (Carbon Nanomembranes with Sub-Nanometer Channels for Molecular Separation in Organic Liquids)
Berichtszeitraum: 2019-10-14 bis 2021-10-13
Global industries strive for higher energy efficiency to achieve smart, sustainable, and inclusive growth. Membrane-based molecular separation has the potential to realize more than 90% energy savings over conventional distillation in the energy-intensive industry. Current challenges that are holding back the realization of these significant energy savings are the lack of membrane materials with high permeance, high selectivity, and high stability. The project aims to address these obstacles by constructing a carbon nanomembrane (CNM) with an ultrathin selective layer, uniform pores, and a stable architecture. CNMs are 2D materials beyond graphene, synthesized by crosslinking of aromatic monolayers. The membrane is one nanometer thick, thus it allows molecules to pass quickly with a low resistance; it mainly comprises carbon, thereby possessing high chemical and thermal stability. Moreover, these materials are built in a versatile and scalable fabrication route, enabling flexible selection of substrates and precursors to customize membrane properties at a molecular level. We will attempt to study the intrinsic membrane structures and characteristics by examining the permeability and selectivity of freestanding CNMs, scale-up nanomembrane materials by constructing nanocomposite CNM membranes comprising mesoporous polymers, as well as understanding the transport mechanism in nanofluidic channels. This project will open a simple avenue to creating 2D membrane materials towards energy-efficient molecular separations.
The project utilizes the unique beneficial properties of carbon nanomembranes to address current challenges in membrane-based molecular separation and to understand the transport mechanisms in nanofluidic channels. The main results achieved so far are outlined below:
(1) Fabrication and characterization of freestanding CNMs for molecular separation. To explore the intrinsic membrane structures and characteristics, we examined the permeability and selectivity of freestanding CNMs made from terphenylthiol for different solvents. A heavy water/n-propanol azeotrope model was introduced to study the molecular separation performance. Single-layer CNMs showed a moderate selectivity of around 300, while the stack of double CNM layers achieved complete rejection of organics. Moreover, solvent mixture experiments demonstrate that the diffusion speed of water across the stacked layer is 10 times slower than through the single-layer membrane. The observed phenomenon is interpreted as a “molecular jam” effect in the interlayer spacing, in which the bulky organic solutes effectively disrupt the collective single-file motion of water. The results demonstrated that these nanomembranes are applicable for dehydration of azeotropic mixtures and revealed the transport behavior under nanoscale confinement.
These results have been reported in a peer-reviewed journal (J. Phys. Chem. Lett. 2020, 11, 238−242). The dissemination of the work has been undertaken through oral presentations at international conferences of 2019 MRS Fall Meeting, International Congress on Membranes and Membrane Processes 2020, North American Membrane Society Annual Meeting 2020, SurfaceScience21 conference of the DPG.
(2) Fabrication and characterization of freestanding CNMs and nanocomposite CNM membranes for osmosis
A major challenge in scaling up 2D material membranes is the transfer of thin films to support, which usually results in micro-scale defects in the film. We addressed this issue by joining bilayer CNMs with micrometer-thick porous polymer support to enhance mechanical stability. This enables us to expand the membrane area from micrometer to millimeter scale, and to test the membrane in real separation systems. Ion transport measurements showed that freestanding CNMs prevent the passage of ionic species including protons. The specific membrane resistance is as high as that of lipid bilayers, ~104 Ω·cm2 in 1 M chloride solutions. Their high resistance suggests that the membrane acts as an efficient barrier against ion movement. Osmosis experiments showed that the CNM nanocomposites can efficiently transport water while excluding ions, through which water flow occurs up to two orders of magnitude faster than through commercial osmosis membranes. The results demonstrated that these nanomembranes are ultra-semipermeable membranes, attributed to the high density of the sub-nm channels created by the cross-linking process. This work stimulates the development of advanced 2D filtration systems towards highly efficient and precise separations.
These results have been reported in a peer-reviewed journal (Adv. Mater. 2020, 32, 1907850). The dissemination of the work has been undertaken through oral presentations at international conferences of 2019 MRS Fall Meeting, International Congress on Membranes and Membrane Processes 2020, North American Membrane Society Annual Meeting 2020, SurfaceScience21 conference of the DPG.
(3) Understanding ionic/molecular transport in nanoconfinement.
2D materials are ideal platforms for studying ionic/molecular transport under nanoscale confinement. Here we investigated the transport of molecules and ions through nanochannels in ultrathin solid-state films. Unusual transport behaviors have been observed in confined spaces. This work will extend the understanding of fluidic transport under nanoconfinement and provide important information for the development of nanofluidic devices for molecular separation and biosensing.
A manuscript has been prepared based on these results and it has been submitted to a peer-reviewed journal in the field of nanoscience and nanotechnology.
(1) Fabrication and characterization of freestanding CNMs for molecular separation. To explore the intrinsic membrane structures and characteristics, we examined the permeability and selectivity of freestanding CNMs made from terphenylthiol for different solvents. A heavy water/n-propanol azeotrope model was introduced to study the molecular separation performance. Single-layer CNMs showed a moderate selectivity of around 300, while the stack of double CNM layers achieved complete rejection of organics. Moreover, solvent mixture experiments demonstrate that the diffusion speed of water across the stacked layer is 10 times slower than through the single-layer membrane. The observed phenomenon is interpreted as a “molecular jam” effect in the interlayer spacing, in which the bulky organic solutes effectively disrupt the collective single-file motion of water. The results demonstrated that these nanomembranes are applicable for dehydration of azeotropic mixtures and revealed the transport behavior under nanoscale confinement.
These results have been reported in a peer-reviewed journal (J. Phys. Chem. Lett. 2020, 11, 238−242). The dissemination of the work has been undertaken through oral presentations at international conferences of 2019 MRS Fall Meeting, International Congress on Membranes and Membrane Processes 2020, North American Membrane Society Annual Meeting 2020, SurfaceScience21 conference of the DPG.
(2) Fabrication and characterization of freestanding CNMs and nanocomposite CNM membranes for osmosis
A major challenge in scaling up 2D material membranes is the transfer of thin films to support, which usually results in micro-scale defects in the film. We addressed this issue by joining bilayer CNMs with micrometer-thick porous polymer support to enhance mechanical stability. This enables us to expand the membrane area from micrometer to millimeter scale, and to test the membrane in real separation systems. Ion transport measurements showed that freestanding CNMs prevent the passage of ionic species including protons. The specific membrane resistance is as high as that of lipid bilayers, ~104 Ω·cm2 in 1 M chloride solutions. Their high resistance suggests that the membrane acts as an efficient barrier against ion movement. Osmosis experiments showed that the CNM nanocomposites can efficiently transport water while excluding ions, through which water flow occurs up to two orders of magnitude faster than through commercial osmosis membranes. The results demonstrated that these nanomembranes are ultra-semipermeable membranes, attributed to the high density of the sub-nm channels created by the cross-linking process. This work stimulates the development of advanced 2D filtration systems towards highly efficient and precise separations.
These results have been reported in a peer-reviewed journal (Adv. Mater. 2020, 32, 1907850). The dissemination of the work has been undertaken through oral presentations at international conferences of 2019 MRS Fall Meeting, International Congress on Membranes and Membrane Processes 2020, North American Membrane Society Annual Meeting 2020, SurfaceScience21 conference of the DPG.
(3) Understanding ionic/molecular transport in nanoconfinement.
2D materials are ideal platforms for studying ionic/molecular transport under nanoscale confinement. Here we investigated the transport of molecules and ions through nanochannels in ultrathin solid-state films. Unusual transport behaviors have been observed in confined spaces. This work will extend the understanding of fluidic transport under nanoconfinement and provide important information for the development of nanofluidic devices for molecular separation and biosensing.
A manuscript has been prepared based on these results and it has been submitted to a peer-reviewed journal in the field of nanoscience and nanotechnology.
1. The project has explored the possible usage of CNM carbon materials for dehydration of organics, fabricated nanomembranes that allow water to pass up to two orders of magnitude faster than commercial osmosis membranes, as well as extending the understanding of fluidic transport under nanoconfinement. These results will stimulate the development of 2D membrane materials towards energy-efficient molecular separations, as well as providing insights into the design of nanofluidic devices for filtration and biosensing.
2. The project integrates the knowledge of physicists, chemists, and engineers, which widely broaden the expertise of the Fellow and provide her with complementary new skills, combining training in nanofabrication and separation engineering. The profoundly interdisciplinary character of the project provides the Fellow with the necessary training to become an independent researcher and open a wide variety of alternatives for her future career development.
2. The project integrates the knowledge of physicists, chemists, and engineers, which widely broaden the expertise of the Fellow and provide her with complementary new skills, combining training in nanofabrication and separation engineering. The profoundly interdisciplinary character of the project provides the Fellow with the necessary training to become an independent researcher and open a wide variety of alternatives for her future career development.