Nanoscale engineering for accessing exotic molecular behavior for application in separations

The interaction of molecules with nanostructured materials leads to a rich behavior [1] which can be exploited for a number of applications including molecular storage and separations [2]. In this presentation, I will discuss a direct experimental study on confinement of water molecules inside isolated sub-2-nm sized single-walled carbon nanotubes (CNTs) leading to highly exotic solid-liquid phase transition behavior with the solid phase of water detected inside CNT at a temperature up to 138°C [3]. The breakdown of the classical theory on the melting point depression of confined fluid (the Gibbs-Thomson effect) would be discussed.
Further, I will discuss the recent efforts in my group to engineer sub-nanometer-sized nanopores in single-layer graphene with precision down to the resolution of 0.3 Å for molecular separation [4,5]. I will show that by suspending these graphene films on porous supports, one can assess extremely fast yet selective molecular crossover rates, leading to record high gas separation performances for critical applications such as carbon capture and hydrogen purification. Finally, I will discuss our recent efforts in the crystallization of metal-organic frameworks (MOFs) based films for application in molecular size-sieving [6]. I will discuss restricting the lattice flexibility of zeolitic imidazolium frameworks-8 (or ZIF-8) by incorporating minuscule defects in its lattice using a rapid post-synthetic treatment [7]. As a result, CO2/N2 and CO2/CH4 selectivities from ZIF-8 films, that are typically lower than 5, could be increased up to 30. Aspects of engineering related to the scale-up of two-dimensional membranes will also be discussed.
(1)Koga et al. Formation of Ordered Ice Nanotubes inside Carbon Nanotubes. Nature 2001, 412, 802–805.
(2)Wang et al. Fundamental Transport Mechanisms, Fabrication and Potential Applications of Nanoporous Atomically Thin Membranes. Nature Nanotechnology 2017, 12 (6), 509–522.
(3)Agrawal et al. Observation of Extreme Phase Transition Temperatures of Water Confined inside Isolated Carbon Nanotubes. Nature Nanotechnology 2017, 12 (3), 267–273.
(4)Huang et al. Single-Layer Graphene Membranes by Crack-Free Transfer for Gas Mixture Separation. Nature Communications 2018, 9 (1), 2632.
(5)Zhao et al. Etching Gas-Sieving Nanopores in Single-Layer Graphene with an Angstrom Precision for High-Performance Gas Mixture Separation. Science Advances 2019, 5 (1), eaav1851.
(6)He et al. Electrophoretic Nuclei Assembly for Crystallization of High-Performance Membranes on Unmodified Supports. Advanced Functional Materials 2018, 28 (20), 1707427.
(7)Babu et al. Restricting Lattice Flexibility in Polycrystalline Metal-Organic Framework Membrane for Carbon Capture. Advanced Materials, just accepted 2019.