Construction of Methylated Hydrazone-Linked 2D Covalent Organic Frameworks for Enhanced Humid CO ₂ Capture

Hydrazone-linked covalent organic frameworks (COFs) are a distinctive class of crystalline porous materials, featuring structural flexibility, abundant heteroatomic sites, and exceptional hydrolytic stability. Conventional syntheses rely on aldehyde–hydrazide condensation, whereas the direct use of aromatic ketones as electrophilic building blocks remains rare due to their low reactivity. Here, we report a ketone-based self-activation strategy for constructing methylated hydrazone COFs (MH–COFs) directly from unsubstituted aromatic ketones with hydrazides. This approach enables rapid antiparallel stacking framework formation, affording hydrazone-linked 2D COFs with high crystallinity and stability. Remarkably, the as-synthesized TAB-DHzOPr exhibited high CO2 uptake of 45.1 cm3 g–1 (1 atm, 273 K) with a high CO2/N2 selectivity of 34.3 (IAST, 15/85, 273 K). More importantly, this COF showed enhanced CO2 capture performance under humid conditions over multiple breakthrough cycles (>4), highlighting the potential of this underexplored ketone-based hydrazone linkage chemistry for the development of functional porous frameworks.