Atomically thin 2D materials, such as graphene, hexagonal boron-nitride, and others, offer new possibilities for ultrathin barrier and membrane applications. While the impermeability of pristine 2D materials to gas molecules, such as He, allows the realization of the thinnest physical barrier, nanoscale vacancy defects in the 2D material lattice manifest as nanopores in an atomically thin membrane. Such nanoporous atomically thin membranes (NATMs) present potential for enabling ultrahigh permeance and selectivity in a wide range of novel separation processes. Herein, the transport properties observed in NATMs are described and recent experimental progress achieved in their fabrication is summarized. Some of the challenges in NATM scale-up for practical applications are highlighted and several opportunities are identified, including the possibility of blending traditional membrane-processing approaches. Finally, a technological roadmap is presented with a contextual discussion for NATMs to progress from research to applications.

Enhancing the membrane water permeability without undermining selectivity has strong potential to reduce the cost of loose nanofiltration (LNF) which attracts growing interest in water and wastewater treatments. Herein, we report a novel polyelectrolyte multilayer LNF membrane with intercalated surfactant self-assemblies. The LNF membranes with integrated surfactant self-assemblies exhibit outstanding permeability to water and selectivity to organic macromolecules such as humic acid and methyl blue. Specifically, the integration of surfactant self-assemblies, SSA, enhances the water permeability by more than 5-fold compared to the reference LNF membrane and, at the same time, increases humic acid rejection from 93% to 98%. The SSA integrated LNF membranes also demonstrate superior performance in terms of permselectivity compared to other membranes in the literature for similar separation (humic acid removal).

We report the surface-initiated ring-opening metathesis polymerization (SiROMP) of hydroxamic acid-containing, metal-chelating polymer thin films. SiROMP of trans-5-norbornene-2,3-dicarbonyl chloride (NBDAC) is introduced as a versatile platform to achieve many functional polymer films via simple exposure of pNBDAC films to reagents. This modification strategy owes its success to the fast and high-yield reaction of acyl chlorides with alcohols, amines, water, and other molecules. The polymerization of NBDAC is performed with monomer in the vapor phase and exhibits rapid kinetics, producing ∼400 nm thick films within 5 min. Because of the high reactivity of the acyl chloride groups in the film, the pNBDAC films are easily modified to produce side chains of carboxylic acids, esters, and amides via the reaction of the acyl group with water, alcohols, and amines, respectively. Exposure of the pNBDAC film to hydroxylamine results in a film with hydroxamic acid functionality that is capable of chelating various metal ions. The chelation process effectively cross-links the polymer chains to greatly improve the thermal and pH stability of the film in solution, elevate resistance against water and ion transfer, and alter the mechanical properties to a more solid-like film.

We present a new route for obtaining surfacetethered polymer films containing pendant catechol functional groups via surface-initiated activators regenerated by electrontransfer atom-transfer radical polymerization (SI-ARGET ATRP) of glycidyl methacrylate (GMA) and post-polymerization modification of the resulting poly(glycidyl methacrylate) (pGMA) films with dopamine. This method enables a high degree of functionalization of pGMA films with catechol groups at a controlled level, depending on the duration of the postpolymerization modification reaction. The dopamine-pGMA films readily absorbs Al 3+ and Zn 2+ ions, as verified by quartz crystal microbalance with dissipation (QCM-D) under continuous flow conditions, and demonstrates a four-fold molar selectivity to Al 3+ over Zn 2+ . The ions desorb from the films upon rinsing with pure deionized (DI) water, which regenerates the catechol sites in the dopamine-pGMA film. Subsequent exposure to metal ions after rinsing steps yields reproducible levels of loading.

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