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.
