Carboxylic anhydride linkers are functional groups containing two carbonyl groups bonded together, and they are used to construct covalent organic frameworks (COFs) via condensation reactions. These linkers contribute to the high thermal and chemical stability of COFs, making them suitable for use in harsh environments and extreme conditions. COFs containing carboxylic anhydride linkers often exhibit excellent gas separation performance due to precise control over pore size and surface chemistry. Applications for these COFs include membrane technology, where their high selectivity and permeability make them ideal for gas separation and purification processes. The versatility of carboxylic anhydride linkers allows the synthesis of COFs with tailored pore structures and functionality, enabling precise control of material performance and properties.