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Polyamide reverse osmosis membranes are indispensable for the worldwide clean water supply. Incorporation of nanomaterials into polyamide separation layer provides an evident methodology to enhance the water flux. However, the desalination performance would be compromised by the inadequate compatibility between the nanomaterial and the polyamide matrix. In this work, we propose a straightforward strategy to use covalent organic frameworks (COF) nanofibers as the efficient nanofiller for the fabrication of high flux polyamide membranes. The COF nanofibers featuring crystalline structures, large surface area and well‐defined micropores are synthesized by a surfactant‐mediated solvothermal method. It is found that the COF nanofibers are able to mediate the interfacial polymerization process via the controlled release of amine molecules. This creates the reduced thickness of the polyamide separation layer. Moreover, the rigid and permanent nanopores of COF could serve as additional channels for water permeation. Benefitting from the low thickness and the additional channels, thus fabricated membranes exhibit a significantly enhanced water flux, while maintaining a slightly improved NaCl rejection. Our work is expected to provide a new insight for the design and fabrication of advanced polyamide reverse osmosis membranes. [ABSTRACT FROM AUTHOR]

Organic solvent nanofiltration (OSN) has become increasingly important in petrochemical and pharmaceutical industries, demanding superior and robust membranes. Herein, we report advanced OSN processes by designing three‐dimensional covalent organic framework (3D COF) membranes through moderated interfacial crystallization. Nanoporous supports work as the moderator allowing the crystallization of 3D COF membranes. The 3D COF features sub‐nanometer and anti‐swelling channels, affording a sharp selectivity to fine targets with an exceptionally high and stable methanol permeance. Thus‐synthesized membrane exhibits a record stability against high‐concentration feeds and long‐term operation for ≈1000 h. Moreover, we unambiguously demonstrate that our membrane holds excellent practicality in purifying active pharmaceutical ingredients from organic liquids. This work reveals the great potential of distinctive 3D COFs in producing prominent OSN membranes for industrial applications. [ABSTRACT FROM AUTHOR]

Intrinsically charged covalent organic frameworks (COFs) afford specific ionic nanochannels for mass transport, and thus become promising platforms to design membranes with unique selectivity. However, internal electrostatic repulsion and large-pore frameworks cause significant barriers that greatly limit membrane performances. Herein, we report a novel strategy to synchronously crystallize and upgrade cationic COF membranes by ion-pairing design. Ion-paired guest molecules are involved in electric-driven interfacial crystallization to offset the charges of the ionic monomers and host frameworks. This host-guest neutralization promotes the crystallization of compact COF membranes. Lateral dimension and charge nature of guest molecules fundamentally affect the ion-pairing efficiency. Tight encapsulation of the large-sized electronegative molecules effectually narrows the molecular sieving channels, yielding a significant elevation in membrane selectivity. The membrane rejection of organic ions with a size larger than 1.2 nm thus can be improved from below 50 % to above 85 % with a water permeance of ∼10 L m−2 h−1 bar−1. Prominently, our membranes demonstrate efficient recovery and pH-dependent release of bioactive pharmaceuticals, with a release rate that is 12 times higher in an acidic solution compared to a neutral environment. This work provides an ion-pairing strategy to regulate COF membranes for pharmaceutical industries and beyond. [Display omitted] • Ion-pairing is designed to crystallize and upgrade COF membranes. • Charged additives can be encapsulated to finely tune the COF membranes. • Encapsulation of the large electronegative molecules promotes membrane selectivity. • Ion-paired COF membranes realize the controlled release of bioactive pharmaceuticals. [ABSTRACT FROM AUTHOR]

Processing two-dimensional (2D) covalent organic frameworks (COFs) into nanofilms has gained widespread attention in water treatment. However, the designed synthesis of COF-based membranes for ion separations still remains a huge challenge though the strategies to produce COF molecular separation membranes have been greatly developed. Herein, we report the construction of bi-layered COF nanofilms for efficient desalination through a simple yet effective secondary growth. The suggested strategy is capable of easily regulating the growth of another COF layer on the pre-synthesized first layer, thus producing crystalline and defect-free bi-layered COF nanofilms with distinct laminated structures. Most importantly, the offset channels are involved at the interface of two nanofilms obtained from the first and secondary growth, which leads to a constricted effective aperture that significantly enhances the ion separation performance. Specifically, the bi-layered COF nanofilms composited with macroporous supports exhibit high rejection rates (~95.8%) to Na 2 SO 4 , observably surpassing the desalination performance of single-layered COF nanofilms (rejection<10%). This work not only develops an ingenious way to fabricate COF-on-COF nanofilms with narrowed channels by tailoring the laminated structure of 2D COFs at the film interface, but also starts an avenue for the adoption of COF platforms for membrane separations with an improved precision. Image 1 • The secondary growth strategy is developed to build bi-layered COF nanofilms. • Nanofilm structures are controllable by adjusting the synthesis conditions. • Offset structures at the film interface enable a narrowed aperture down to ~0.71 nm. • The bi-layered COF nanofilms exhibit a greatly boosted desalination performance with a reasonable flux. [ABSTRACT FROM AUTHOR]