Differences in water and vapor transport through angstrom-scale pores in atomically thin membranes

Abstract

The transport of water through nanoscale capillaries/pores plays a prominent role in biology, ionic/molecular separations, water treatment and protective applications. However, the mechanisms of water and vapor transport through nanoscale confinements remain to be fully understood. Angstrom-scale pores (~2.8–6.6 Å) introduced into the atomically thin graphene lattice represent ideal model systems to probe water transport at the molecular-length scale with short pores (aspect ratio ~1–1.9) i.e., pore diameters approach the pore length (~3.4 Å) at the theoretical limit of material thickness. Here, we report on orders of magnitude differences (~80×) between transport of water vapor (~44.2–52.4 g m−2 day−1 Pa−1) and liquid water (0.6–2 g m−2 day−1 Pa−1) through nanopores (~2.8–6.6 Å in diameter) in monolayer graphene and rationalize this difference via a flow resistance model in which liquid water permeation occurs near the continuum regime whereas water vapor transport occurs in the free molecular flow regime. We demonstrate centimeter-scale atomically thin graphene membranes with up to an order of magnitude higher water vapor transport rate (~5.4–6.1 × 104 g m−2 day−1) than most commercially available ultra-breathable protective materials while effectively blocking even sub-nanometer (>0.66 nm) model ions/molecules.

The parameter space for scalable integration of atomically thin graphene with Nafion for proton exchange membrane (PEM) applications

“…Graphene grown via chemical vapor deposition (CVD) on the other hand also exhibits proton conductance of B5 mS cm À2 over micron-scale areas, 16 but centimeter-scale CVD graphene shows much higher proton conductance 41 S cm À2 due to presence of intrinsic defects. 10,[16][17][18] The ability to precisely control intrinsic defects in CVD graphene [18][19][20][21] via bottom-up synthesis presents potential for advancing PEMs by mitigating persistent issues of reactant crossover via steric hinderance to transport of atoms and hydrated ions while allowing enhanced proton permeation through defects. 18,22 A facile and scalable approach is to incorporate an atomically thin layer of monolayer CVD graphene with precisely controlled intrinsic defects with Nafion to mitigate crossover issues prevalent in polymeric proton exchange membranes while simultaneously maintaining high proton transport (area specific resistance o1 O cm 2 or conductance 41 S cm À2 ) for practical PEM applications.…”

“…Graphene grown via chemical vapor deposition (CVD) on the other hand also exhibits proton conductance of ∼5 mS cm −2 over micron-scale areas, 16 but centimeter-scale CVD graphene shows much higher proton conductance >1 S cm −2 due to presence of intrinsic defects. 10,16–18 The ability to precisely control intrinsic defects in CVD graphene 18–21 via bottom-up synthesis presents potential for advancing PEMs by mitigating persistent issues of reactant crossover via steric hinderance to transport of atoms and hydrated ions while allowing enhanced proton permeation through defects. 18,22…”

High‐Performance Hemofiltration via Molecular Sieving and Ultra‐Low Friction in Carbon Nanotube Capillary Membranes

“…The diffusion-driven solute transport measurements across the fabricated CNT membrane were performed as previously reported in detail elsewhere. [52,[68][69][70][71][72] The setup used for diffusion measurements was a customized 7 mL Side-Bi-Side glass diffusion cell (PermeGear, Inc.) with a 5 mm orifice as shown in Figure S1, Supporting Information. The CNT membrane (≈1.6 cm diameter) was installed between two diffusion cells, followed by clamping the diffusion system.…”

Selective Photonic Gasification of Strained Oxygen Clusters on Graphene for Tuning Pore Size in the Å Regime

“…The zero-dimensional nature of Å-scale pores in graphene makes them attractive for exploring and manipulating molecular transport − at the atomic scale for applications in molecular and ionic separation, ,− sensing, , molecular valves, and phase transitions under confinement. ,, In particular, the possibility to finely tune the pore size and pore density in graphene is highly sought after for advanced applications in gas- and liquid-phase separation. ,,, Computational studies on molecular transport across porous graphene have reported highly attractive separation performances. − Motivated by these results, efforts have been made to achieve Å-scale pores with a narrow size distribution by several physical and chemical routes. These include direct carbon knockout by focused ion beam techniques, , electron beam methods, and plasma procedures, − as well as carbon gasification through chemical etching using KMnO 4 , O 3 , , O 2 , and a combination of these. ,, Oxidation chemistry is extremely attractive for pore formation because of its high uniformity and ease of implementation, which has resulted in the commercialization of oxidized graphene in the form of graphene oxide (GO) and reduced GO (rGO) .…”