Carboxyl functionalized covalent organic framework material for selective adsorption of methylene blue in aqueous solutions

In this paper, M-TzDha-COF composed of 4,4′,4″-(1,3,5-triazine-2,4,6-triyl) trianiline (Tz) and 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (Dha) was synthesized by grafting carboxyl groups onto COF framework via the solvent-free esterification. M-TzDha-COF retains the porous structure and has good crystallinity and high thermal stability. M-TzDha-COF exhibits selective adsorption and efficient removal of methylene blue dye with the maximum adsorption capacity of 95 mg·g −1 . M-TzDha-COF can adsorb methylene blue rapidly and maintain high adsorption efficiency after several cyclic applications. The adsorption of methylene blue on M-TzDha-COF is consistent with the pseudo-second-order adsorption kinetic model and Langmuir adsorption model. Adsorption is caused by three interactions: π-π stacking between the triazine group and methylene blue, electrostatic interaction between the carboxyl group and the methylene blue cationic portion, and hydrogen bonding interaction. Fast kinetics, high adsorption capacity and good reusability make carboxyl functionalized COF have great potential in removing methylene blue dye from water.