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Water contamination by organic dyes, heavy metal ions, and nanoscale particles poses a severe threat to ecosystems and human health, necessitating the development of versatile and robust filtration materials. Covalent organic frameworks (COFs), with their high porosity, tunable surface chemistry, and structural diversity, offer unique opportunities for multifunctional water purification. Here, we report a facile, one-pot, and scalable aqueous synthesis of imine- and β-ketoenamine-linked COFs in the form of freestanding, mechanically robust gels. A total of 31 freestanding COF gels with different molecular structures were successfully obtained, including 25 that are highly crystalline and 6 that are less crystalline or amorphous. Systematic investigation of synthesis conditions revealed that the type of linkage and reaction temperature significantly influenced the gelation process: room temperature favored imine-linked COF gels, whereas elevated temperature promoted β- ketoenamine-linked COF formation. The resulting COF gels exhibited high surface areas (up to 2127 m²/g), tunable pore sizes, and robust elastic networks. Taking advantage of their hierarchical porosity and high stability, the COF gels were employed in a filtration system, which enabled efficient removal of diverse pollutants, including Rhodamine B, Cr³⁺ ions, and ultrafine particles under continuous flow. These findings establish aqueous synthesis and shaping of COF materials as multifunctional platforms for next-generation water purification, capable of efficiently removing diverse pollutants and suitable for applications in industrial wastewater treatment, environmental remediation, and potable water production.

membranes using novel materials and techniques, there is an increasing need to evaluate the practical viability of innovative membranes at the early stages of development. In many materials research laboratories, access to professionally manufactured membrane-evaluation systems may be limited. Here we present a pressure-driven filtration system for evaluation of nanofiltration membranes, that can be constructed from 3D-printed parts and widely available off-the-shelf components at a cost of approximately 60 €. The system uses a stirred cross-flow design capable of circulating the feed solution in the filter cell and maintaining a stable solute concentration during extended filtration experiments—as in conventional cross-flow cells. It is suitable for filtration of aqueous solutions containing dyes, inorganic salts, and dilute acids. Validation was performed by filtering a 2000 mg L^-1 MgSO₄ solution through a Veolia RL membrane at 7.6 bar, achieving a 96.5% rejection rate and a permeance of 7.5 L m^-2 h^-1 bar^-1 after 24 hours of continuous operation.

Covalent organic frameworks (COF) are promising active materials for pressure-driven separation membranes, owing to their high porosity, uniform pore structure, tunability and stability. Achieving scalable fabrication of COF layers on porous substrates in an essential step towards the large scale production and application of COF thin film composite (TFC) membranes. Here, we present a scalable precursor casting strategy for fabricating TpPa(SO₃H)-COF on porous polytetrafluoroethylene (PTFE) substrates. While the COF layers exhibited inhomogeneous morphology and thickness, the membranes were robust and capable of fully rejecting Congo red dye from an aqueous solution. Thus, the fabrication strategy outlined here demonstrates potential for large scale production of COF-based TCF membranes by precursor casting.

Covalent organic framework (COF) membranes hold significant promise for applications in separation, catalysis, and energy conversion; however, their industrial adoption has been hindered by the lack of scalable and efficient fabrication methods. Here, we present a fast, versatile, and broadly applicable strategy for fabricating free-standing and flexible COF membranes by casting precursor suspensions, followed by heat treatment under controlled humidity. This approach enables the fabrication of COF membranes with lateral dimensions up to several square decimeters and thicknesses that are tunable down to submicron levels within 1 h. It demonstrates remarkable versatility for producing a family of ketoenamine-linked COF membranes through the condensation of 1,3,5-triformylphloroglucinol with various amine monomers differing in length, side groups, and geometry. The resulting crack-free COF membranes exhibit high mechanical strength, with ultimate tensile strength up to 60 MPa and Young’s modulus up to 1.7 GPa, as well as exceptionally high porosity, with Brunauer–Emmett–Teller (BET) surface areas reaching up to 2226 m2 g–1. More importantly, the morphology, porosity, and crystallinity of the membranes can be finely tuned by modulating the heating conditions. The membranes with optimized microstructures demonstrate excellent separation performance, achieving over 99% rejection in nanofiltration of aqueous dye solutions, and a separation factor of 11 with an H2 permeance of 2857 GPU in H2/CO2 gas separation. This approach provides a scalable and effective pathway toward large-scale COF membrane manufacturing for advanced molecular separations and other membrane-based technologies.