Water-Steam-Assisted Synthesis of Imine-Linked COF-432 for Atmospheric Water Harvesting

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Covalent organic frameworks (COFs), featuring ordered porous structures and tunable pore chemistry, have emerged as promising adsorbents for atmospheric water harvesting. However, conventional solvothermal synthesis relies on large amounts of organic solvents and prolonged reaction times, hindering sustainable and scalable production. Herein, a steam-assisted synthetic strategy is developed for the preparation of COF-432 using water as the steam medium. By optimizing the steam source, acetic acid dosage, reaction temperature, and reaction time, highly crystalline COF-432 was obtained within 6 h, significantly reducing the reaction time compared with the conventional 72 h solvothermal process. The steam-assisted product exhibited comparable structural characteristics, porosity, thermal stability, and water adsorption performance to the solvothermal counterpart. It displayed a characteristic Type V water adsorption isotherm with a sharp adsorption step at P/P0 ≈ 0.34 and a water capacity of 0.26 g g–1 under the practically relevant humidity range of P/P0 = 0.2–0.4. Gram-scale synthesis was achieved with a high yield of 93.0%, while preserving crystallinity and adsorption properties. The resulting COF could also be processed into mechanically robust pellets without compromising framework integrity or water-harvesting behavior. This work provides a rapid, scalable, and sustainable synthetic route toward COFs for atmospheric water harvesting applications.