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Covalent organic frameworks (COFs) have evinced a potential solution that promises for fast and efficient molecular separation due to the presence of orderly arranged pores and regulable pore apertures. Herein, the synthesized COF (TPB-DMTP-COF) with the pore aperture matching the pore size of the nanofiltration (NF) membrane was utilized to modulate the physicochemical characters of the polyamide (PA) membranes. It is demonstrated that COFs with superior polymer affinity and hydrophilicity not only circumvent the nonselective interfacial cavities but also improve the hydrophilicity of the resultant thin-film nanocomposite (TFN) membranes. Furthermore, the predeposited COF layer is able to slow down the diffusion rate toward the reaction boundary through hydrogen bonding, which is consistent with the results of molecular dynamic (MD) and dissipative particle dynamic (DPD) simulations. In this context, COF-modulated TFN membranes show a roughened and thickened surface with bubble-shaped structures in contrast to the nodular structure of original polyamide membranes. Combined with the introduced in-plane pores of COFs, the resultant TFN membranes display a significantly elevated water permeance of 35.7 L m

Synthetic membranes universally exhibit a pernicious trade-off effect, on which there exists an upper bound between permeability and selectivity. Tremendous efforts are made to design crumpled membranes to further break through the bottleneck. In this work, we proposed that a nano-pleated membrane surface with ridged nanostructures enables rapid transport of water molecules. Here, a root-like, ultrathin thin film composite (TFC) membrane was carefully designed via incorporation of a sacrificial ZIF-L layer into a polyamide layer, followed by its removal in a weak acid solution. The best performing membranes displayed ultrahigh water permeances of 48.9 L m−2 h−1 bar−1 with a comparable rejection of sodium sulfate, surpassing the upper limit of conventional desalting membranes. The utilization of sacrificial ZIF-L templates in the regulation of the nanofilm morphology is suggested to be promising for fabrication of highly permeable NF membranes.

An efficient molecular-level separation membrane with high permeability and superior selectivity is of pivotal significance for precise molecular/ion separation. However, there still exists a technical challenge to accurately control the membrane pore apertures at nanoscale dimensions for molecular separations. The use of two-dimensional (2D) materials featuring single-layered/few-layered thickness is favored for shortening the transport pathway for solvent molecules. Owing to their facile fabrication process, tunable pore size, and versatile functions, 2D material-based membranes show great potential to overcome this challenge for rapid and efficient separations via the combined effect of pore aperture and pore surface functionalization. Recently, 2D non-carbon-based nanomaterials have been extensively explored as effective building blocks to construct high-performance membranes. This chapter outlines the characteristics and synthesis methods of several non-carbon-based 2D materials like MOFs, COFs, and MXene. The use of these 2D materials for membrane design and their applications for liquid separation is summarized and discussed. Subsequently, the challenges of non-carbon-based 2D materials used in liquid separation and the future development direction are highlighted.

Porous organic polymers (POPs) have evinced a huge potential for membrane-based separations owing to their impressive surface areas, high mesopore ratio, superior chemical stabilities, and catalytic abilities. In this study, for the first time, an o-hydroxy porous organic polymer (POP) thin film was in situ generated atop a (polyacrylonitrile) HPAN membrane support via diazo-coupling reaction under mild conditions. Analysis by FT-IR, XPS and SEM confirmed the successful formation of a coherent, thin POP nanofilm. Zeta potentials and water contact angle measurements demonstrated that the resultant POP film was hydrophilic (water contact angle = 48°) and negatively charged because of the abundance of hydroxyl groups. The roles of synthesis parameters (e.g., the solution pH and the reaction time) in the membrane microstructure and separation performance were explored in detail. The best-performing composite membranes show a high pure water permeability (66.5 L m−2h−1 bar−1), superior dye retentions (RCR = 99.6%, RDR = 98.0%, RMB = 98.8%), and low divalent salt retention (

Interfacial polymerization is the gold standard for manufacturing thin film composite (TFC) membranes for nanofiltration (NF) and reverse osmosis (RO). However, typical polyamide (PA) thin film composite (TFC) membranes fabricated by interfacial polymerization are inappropriate for dye wastewater zero discharge and are susceptible to oxidizing agents. In this study, by using a new N-rich amine monomer 3,5-diamino-1,2,4-triazole (DAT), a novel PA TFC membrane was fabricated for the separation of dyes and salts. It is speculated that the unique molecular structure of DAT can conducive to the formation of a less compact polyamide layer with improved chlorine resistance. The optimum membrane shows an ultrahigh pure water permeability (95.1 L/m2·h·bar) and an excellent dye/salt separation selectivity for Congo red and NaCl (rejection, 99.1% and 5.8%, respectively). This is superior to that of the two commonly used dye/salt separation commercial membranes (Sepro NF 6 and NF 2A, Ultura). Furthermore, the resultant DAT/TMC TFC membranes maintained their original separation efficacy after 120 h of immersion in NaClO solution, demonstrating their good chlorine resistance. In summary, this study not only expands the application of interfacial polymerization, but also provides a new inspiration for the preparation of advanced membranes for efficient dye/salt separation.

Membrane-based separation processes can efficiently capture CO2 and reduce energy consumption. However, the synthesis of a CO2-philic material which can replace traditional gas separation materials for advanced membrane separation faces numerous challenges. In this paper, we report the incorporation of porous organic polymers (POPs) and low-molecular-weight polyethylene glycol (PEG 400) into Pebax 1657 for the fabrication of a CO2-philic mixed matrix membrane for CO2 capture. The POPs, which contained azo bonds and phenolic hydroxyl groups, exhibited CO2-philic and N2-phobic properties. PEG 400, which possesses ethylene oxide (EO) units with a polar ether group, enhanced the CO2 permeability and CO2/N2 selectivity. This CO2-philic membrane showed CO2 permeability of 392 Barrer and CO2/N2 selectivity of 112, which surpassed the upper bound (2019). This membrane could be a widely applicable tool for improving CO2 capture with advanced membranes.