Modification of covalent organic framework by hydrolysis for efficient and selective removal of organic dye

The efficient removal of organic dyes from wastewater is still a major challenge, especially for the massive production of dyeing technology. Herein, polyimide-based covalent-organic frameworks (COFs) with a highly ordered conjugated architecture are synthesized through the condensation reaction of pyromellitic dianhydride (PMDA) with tris (4-aminophenyl) amine (TAPA). Due to a repeated cyclic structure, COFs subjected to alkaline hydrolysis can offer a high density of negatively charged carboxylate anions as adsorption sites for cationic methylene blue (MB) dye through electrostatic interactions. The maximum adsorption capacity of MB on hy-drolyzed COFs is measured to be 315.6 mg/g at pH = 10 and room temperature. Significantly, hydrolyzed COFs exhibit superior adsorption selectivity for MB in a mixture solution with methyl orange (MO) and rhodamine B (RhB). Overall, hydrolyzed COFs are good candidates to serve as an efficient adsorbent for the removal of MB with a high selectivity in the posttreatment of the dyeing process. The employment of COFs with a highly active surface in this study provides new insights for the future development of efficient adsorbents for organic dyes.