Pore surface engineering of covalent organic frameworks by simultaneously appending amine group and tailoring pore size for efficient adsorption of diclofenac sodium

Herein, a facile strategy was proposed to construct efficient covalent organic frameworks (COFs) adsorbents by grafting affinity groups linked with different lengths of carbon chains as post-synthetic modification, simultaneously achieving the regulation of pore size and functional groups. Specifically, three amine-functionalized COFs were synthesized by the thiol-ene "click" reaction of vinyl-COF, which simultaneously appended amino groups onto the pore wall and tuned the pore size, to effectively capture diclofenac sodium (DS) from water. The constructed COFs, typically COF-3-NH2, exhibited remarkably rapid and efficient removal of DS, with a rate constant k2 of 0.0084 g/mg/min and a maximum adsorption capacity of 410.0 mg/g, superior to most adsorbents previously reported. The impressive performance of COF-3-NH2 was attributed to the synergistic effects arising from densely grafted charged amino groups within ordered pores of suitable size, leading to rapid diffusion and strong affinity towards guest molecules. Electrostatic and π-π stacking interactions played a vital role in capturing DS. COF-3-NH2 could selectively adsorb DS from a mixture. Moreover, the spent COF-3-NH2 could be regenerated by methanol for successive reuse. The adsorbent could efficiently remove DS from real wastewater as well, showing potential for micropollutant removal in practical applications. This work revealed the potential of pore surface engineered COFs as efficient adsorbents for the removal of organic pollutants from contaminated water.