We fabricated a thin-film composite (TFC) forward osmosis (FO) membrane with an ultrathin spray-coated carbon nanotube (CNT) interlayer. The impact of the CNT interlayer on the polyamide (PA) layer structural properties and transport behavior in FO were investigated. Results indicate that the CNT interlayer provides an interface which enables the formation of a highly permeable and selective PA layer with a large effective surface area for water transport, while inhibiting the formation of a flowerlike PA structure inside the substrate pores. The TFC-FO membrane with the CNT interlayer exhibited a much greater water flux than previously reported for FO membranes, while maintaining comparable salt rejection. Specifically, a membrane perm-selectivity or ratio of water (A) to salt permeability coefficients (B) (A/B value) of 39 bar −1 was achieved for the TFC-PA-CNT membrane. Implications of the results for the fabrication of highperformance TFC-FO membranes are further discussed.

A triple-layered TFC nanofiltration (NF) membrane consisting of a polyamide (PA) top layer covered on a poly(ether sulfone) microfiltration membrane with a carbon nanotube (CNT) interlayer was fabricated via interfacial polymerization. The structure and properties of the PA active layer could be finely tailored by tuning the interfacial properties and pore structure of the CNT interlayer, including its surface pore size and thickness, thus improving its NF performance. This TFC NF membrane exhibited a high divalent salt rejection (the rejection of Na 2 SO 4 and MgSO 4 solution >98.3%) and dye rejection (the rejection of methyl violet (MV) >99.5%) with a high pure water flux of around 21 L m −2 h −1 bar −1 . Excitingly, this membrane also showed excellent selectivity to both mono/divalent salt ion (the selectivity of Cl − /SO 4 2− is as high as 85.5) and NaCl/dye solution (the selectivity of NaCl/MV is more than 123.5), which are much higher than most of other commercial and reported NF membranes. Moreover, this membrane also showed a good separation performance and long-term stability during a continuous NF process for a salt/dye mixture solution. This triple-layered TFC NF membrane showed a great promise for applications in both wastewater treatment and dyes recycling.

Nanofluidic membranes have been demonstrated as promising candidates for osmotic energy harvesting. However, it remains a long-standing challenge to fabricate high-efficiency ion-permselective membranes with well-defined channel architectures. Here, we demonstrate high-performance osmotic energy conversion membranes based on oriented two-dimensional covalent organic frameworks (COFs) with ultrashort vertically aligned nanofluidic channels that enabled efficient and selective ion transport. Experiments combined with molecular dynamics simulations revealed that exquisite control over channel orientation, charge polarity, and charge density contributed to high ion selectivity and permeability. When applied to osmotic energy conversion, a pair of 100 nm thick oppositely charged COF membranes achieved an ultrahigh output power density of 43.2 W m–2 at a 50-fold salinity gradient and up to 228.9 W m–2 for the Dead Sea and river water system. The achieved power density outperforms the state-of-the-art nanofluidic membranes, suggesting the great potential of oriented COF membranes in the fields of advanced membrane technology and energy conversion.

Pore size uniformity is one of the most critical parameters in determining membrane separation performance. Recently, a novel type of conjugated microporous polymers (CMPs) has shown uniform pore size and high porosity. However, their brittle nature has prevented them from preparing robust membranes. Inspired by the skin-core architecture of spider silk that offers both high strength and high ductility, herein we report an electropolymerization process to prepare a CMP membrane from a rigid carbazole monomer, 2,2’,7,7’-tetra(carbazol-9-yl)-9,9’-spirobifluorene, inside a robust carbon nanotube scaffold. The obtained membranes showed superior mechanical strength and ductility, high surface area, and uniform pore size of approximately 1 nm. The superfast solvent transport and excellent molecular sieving well surpass the performance of most reported polymer membranes. Our method makes it possible to use rigid CMPs membranes in pressure-driven membrane processes, providing potential applications for this important category of polymer materials.

Polymer membranes typically possess a broad pore-size distribution that leads to much lower selectivity in ion separation when compared to membranes made of crystalline porous materials; however, they are highly desirable because of their easy processability and low cost. Herein, we demonstrate the fabrication of ionsieving membranes based on a polycarbazole-type conjugated microporous polymer using an easy to scale-up electropolymerization strategy. The membranes exhibited high uniform sub-nanometer pores and a precisely tunable membrane thickness, yielding a high ion-sieving performance with a sub-1 Å size precision. Both experimental results and molecular simulations suggested that the impressive ionsieving performance of the CMP membranes originates from their uniform and narrow pore-size distribution.