Nanoporous Atomically Thin Graphene Filters for Nanoscale Aerosols

Protein-Enabled Size-Selective Defect-Sealing of Atomically Thin 2D Membranes for Dialysis and Nanoscale Separations

Atomically thin 2D materials present the potential for advancing membrane separations via a combination of high selectivity (from molecular sieving) and high permeance (due to atomic thinness). However, the creation of a high density of precise nanopores (narrow-size-distribution) over large areas in 2D materials remains challenging, and nonselective leakage from nanopore heterogeneity adversely impacts performance. Here, we demonstrate protein-enabled size-selective defect sealing (PDS) for atomically thin graphene membranes over centimeter scale areas by leveraging the size and reactivity of permeating proteins to preferentially seal larger nanopores (≥4 nm) while preserving a significant amount of smaller nanopores (via steric hindrance). Our defect-sealed nanoporous atomically thin membranes (NATMs) show stability up to ∼35 days during size-selective diffusive separations with a model dialysis biomolecule fluorescein isothiocyanate (FITC)-Ficoll 70 in phosphate buffer saline (PBS) solution as well as outperform state-of-the-art commercially available dialysis membranes (molecular-weight-cutoff ∼3.5-5 kDa and ∼8-10 kDa) with significantly higher permeance for smaller solutes KCl (∼0.66 nm) ∼5.1-6 × 10-5 ms-1 and vitamin B12 (B12, ∼1.5 nm) ∼2.8-4 × 10-6 ms-1 compared to small protein lysozyme (Lz, ∼4 nm) ∼4-6.4 × 10-8 m s-1, thereby allowing unprecedented selectivity for B12/Lz ∼70 and KCl/Lz ∼1280. Our work introduces proteins as nanoscale tools for size-selective defect sealing in atomically thin membranes to overcome persistent issues and advance separations for dialysis, protein desalting, small molecule separations/purification, and other bioprocesses.

Ultra-thin proton conducting carrier layers for scalable integration of atomically thin 2D materials with proton exchange polymers for next-generation PEMs

Scalable approaches for synthesis and integration of proton selective atomically thin 2D materials with proton conducting polymers can enable next-generation proton exchange membranes (PEMs) with minimal crossover of reactants or undesired species while maintaining adequately high proton conductance for practical applications. Here, we systematically investigate facile and scalable approaches to interface monolayer graphene synthesized via scalable chemical vapor deposition (CVD) on Cu foil with the most widely used proton exchange polymer Nafion 211 (N211, ∼25 μm thick film) via (i) spin-coating a ∼700 nm thin Nafion carrier layer to transfer graphene (spin + scoop), (ii) casting a Nafion film and cold pressing (cold press), and (iii) hot pressing (hot press) while minimizing micron-scale defects to <0.3% area. Interfacing CVD graphene on Cu with N211 via cold press or hot press and subsequent removal of Cu via etching results in ∼50% lower areal proton conductance compared to membranes fabricated via the spin + scoop method. Notably, the areal proton conductance can be recovered by soaking the hot and cold press membranes in 0.1 M HCl, without significant damage to graphene. We rationalize our finding by the significantly smaller reservoir for cation uptake from Cu etching for the ∼700 nm thin carrier Nafion layer used for spin + scoop transfer compared to the ∼25 μm thick N211 film for hot and cold pressing. Finally, we demonstrate performance in H2 fuel cells with power densities of ∼0.23 W cm-2 and up to ∼41-54% reduction in H2 crossover for the N211|G|N211 sandwich membranes compared to the control N211|N211 indicating potential for our approach in enabling advanced PEMs for fuel cells, redox-flow batteries, isotope separations and beyond.

Advancements of Nanotechnology and Nanomaterials in Environmental and Human Protection for Combatting the COVID-19 During and Post-pandemic Era: A Comprehensive Scientific Review

In December 2019, an outbreak of unknown pneumonia emerged in Wuhan City, Hubei Province, China. It was later identified as the SARS-CoV-2 virus and has since infected over 9 million people in more than 213 countries worldwide. Massive papers on the topic of SARS-CoV-2 that have already been published are necessary to be analyzed and discussed. This paper used the combination of systematic literature network analysis and content analysis to develop a comprehensive discussion related to the use of nanotechnology and materials in environmental and human protection. Its is shown that various efforts have been made to control the transmission of this pandemic. Nanotechnology plays a crucial role in modern vaccine design, as nanomaterials are essential tools for antigen delivery, adjuvants, and mimics of viral structures. In addition, nanomaterials and nanotechnology also reported a crucial role in environmental protection for defence and treating the pandemic. To eradicate pandemics now and in the future, successful treatments must enable rapid discovery, scalable manufacturing, and global distribution. In this review, we discuss the current approaches to COVID-19 development and highlight the critical role of nanotechnology and nanomaterials in combating the virus in the human body and the environment.

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

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 × 10⁴g m^-2 day^-1) than most commercially available ultra-breathable protective materials while effectively blocking even sub-nanometer (>0.66 nm) model ions/molecules.