Achieving both crystallinity and stability is challenging for covalent organic frameworks (COFs) as the reversible reaction required for enhancing crystallinity compromises stability. Amide linkages, a type of chemically stable bond for COF construction, are predominantly synthesized via postmodifications. This work presents a direct and convenient method for synthesizing highly crystalline amide-linked COFs via the ester-amine exchange reaction. The reaction is irreversible, as demonstrated by the investigation of model reactions and COFTAPT-TTPF polymerization process. The water absorption capacity of COFTAPT-TTPF was 0.56 g/g at 25 °C and 94% relative humidity. Meanwhile, via direct synthesis, we grew COFTAPT-TTPF on anodized aluminum oxide membranes to form COF@AAO composite membranes. The composite membrane achieved an output power density of 7.70 W/m2 under a 50-fold salinity gradient in osmotic energy conversion. This direct polymerization protocol improves the convenience and accessibility of amide-linked COFs.
Li et al. (Mon,) studied this question.