Elucidating Ultrafast Molecular Permeation through Well-Defined 2D Nanochannels of Lamellar Membranes.

Lamellar membranes with well-defined 2D nanochannels show fast, selective permeation, but the underlying molecular transport mechanism is unexplored. Now, regular robust MXene Ti3 C2 Tx lamellar membranes are prepared, and the size and wettability of nanochannels are manipulated by chemically grafted hydrophilic (-NH2 ) or hydrophobic (-C6 H5 , -C12 H25 ) groups. These nanochannels have a sharp difference in mass transfer behavior. Hydrophilic nanochannels, in which polar molecules form orderly aligned aggregates along channel walls, impart ultrahigh permeance (>3000 L m-2 h-1 bar-1 ), which is more than three times higher than that in hydrophobic nanochannels with disordered molecular configuration. In contrast, nonpolar molecules with disordered configuration in both hydrophilic and hydrophobic nanochannels have comparable permeance. Two phenomenological transport models correlate the permeance with the mass transport mechanism of molecules that display ordered and disordered configuration.

Nanoparticle-Assembled Thin Film with Amphipathic Nanopores for Organic Solvent Nanofiltration.

Polymeric thin film composite (TFC) membranes have been proven promising for a wide range of separation applications. However, their development is significantly hindered by low permeance (below 8.0 L m-2 h-1 bar-1). Here, we report the fabrication of new films with nanoparticle-assembled structure via interfacial polymerization using quantum dots (QDs) as building blocks. The tailored QDs with hydrophobic and hydrophilic regions permit cross-linking into nanoparticle-assembled defect-free thin films. Significantly, amphipathic QDs show good affinity to polar and nonpolar molecules, facilitating their fast dissolution into film. Meanwhile, the nanopores (∼1.4 nm) render fleet diffusion of molecules, which highly promotes the transfer of molecules within the film. This synergetic effect endows the resultant TFC membrane with high permeance, over 2 orders of magnitude higher than the conventional polyamide films. The permeances for acetonitrile and n-hexane reach 46.9 and 50.8 L m-2 h-1 bar-1, respectively. We demonstrate that films fabricated by hydrophilic and hydrophobic QDs exhibit different molecular transfer mechanisms, and the corresponding model equations are established. The film fabricated by amphipathic QDs shows a combination transfer mechanism of the two models. Furthermore, those QD-based TFC membranes display favorable structural and operational stability, holding promise for industrial separation applications.

Adsorption-Assisted Interfacial Polymerization toward Ultrathin Active Layers for Ultrafast Organic Permeation.

Thin-film composite (TFC) membranes show exceptional permeation properties of key importance for many separations. However, their design and development need ultrathin and defect-free nanofilms as the active layer to alleviate the bottleneck of permeation-rejection trade-off. Here, a 25 nm thick film is fabricated on a porous support by introducing polydopamine (PDA) as an adsorption layer, imparting a unique adsorption-assisted interfacial polymerization (IP) strategy. The PDA layer efficiently captures and enriches amine monomers even from ultradilute solution toward uniform stacking on the support, thus generating ultrathin and defect-free films after polymerization. This is superior to the defective one from conventional IP. Such an active layer features ultrafast permeation for organics, favorable solute rejection, and excellent operation stability. Particularly, the acetone permeance of this new TFC membrane reaches 96.3 L m-2 h-1 bar-1, which exceeds that from conventional IP by more than 10 times, ranking among one of the highest performances reported to date. More significantly, the pernicious permeation-rejection trade-off of the TFC membrane is thus alleviated. Besides, this strategy is facile, versatile, and easy to scale-up, giving controllable physical and chemical structures to the active layer. This study may pave a way to well-design highly efficient film materials for various transport and separation applications.