Maximizing Porosity and Water Sorption in Covalent Organic Frameworks via β-Ketoenamine Linkages

Controlling the crystallinity and porosity of 2D covalent organic frameworks (2D COFs) is crucial for their applications in science and technology. Herein, the construction of 2D COFs, COF-TP-X, is reported using a multicomponent reaction strategy that introduces β-ketoenamine linkages into isostructural imine-linked COFs. This approach yields materials with exceptional crystallinity, stability, and tunable hydrophilicity. The integration of β-ketoenamine linkages promotes intralayer planarity via NH⋯O hydrogen bonds and enhances π-electronic conjugation within and between layers. By partially substituting (43 mol%) 1,3,5-triformylbenzene with 1,3,5-triformylphloroglucinol, an outstanding gravimetric surface area of 1,984 m² g⁻¹ and a pore volume of 0.8 cm³ g⁻¹ are achieved—a remarkable two-fold increase compared to mono-linker counterparts. Moreover, COF-TP-X exhibits an exceptional water uptake capacity of 0.70 g g⁻¹ (70 wt.%) and superior hydrolytic stability, as confirmed by over 200 cycles of water adsorption–desorption experiments. Furthermore, molecular simulations reveal the significant role of electrostatic interactions between β-ketoenamine linkages in enhancing interlayer stacking and crystallinity. The findings provide key insights into COF design via a mixed-linker strategy, representing a significant advancement in developing COFs with superior performance and paving the way for their industrial applications.