A sulfonate-functionalized covalent organic framework for record-high adsorption and effective separation of organic dyes

The emerging global water crisis necessitates the development of solid adsorbents for the removal of organic pollutants from wastewater. Herein, we develop an anionic sulfonate-functionalized covalent organic framework (COF), termed TpStb-SO3Na, by the Schiff-base condensation between 2,4,6-triformylphloroglucinol (Tp) and 4,4′-diaminostilbene-2,2′-disulfonic acid (Stb-SO3H) under solvothermal conditions in the presence of sodium acetate. Thanks to the dense sulfonate groups in the periodic one-dimensional channels, the negatively charged TpStb-SO3Na displayed rapid kinetics (average ∼ 99% uptake in merely 10 min) and ultrahigh adsorption capacities for multiple cationic dyes including methylene blue (MB, 1078 mg g−1), crystal violet (CV, 1861 mg g−1), malachite green (MG, 5857 mg g−1) and janus green B (JGB, 1339 mg g−1) at room temperature. Noteworthy, the adsorption capacities of TpStb-SO3Na toward CV, MG, and JGB were the record-high values among the documented COFs, metal–organic frameworks (MOFs), and other benchmark adsorbents. In addition, the adsorption behaviors of MB, CV, MG, and JGB on TpStb-SO3Na obeyed the pseudo-second-order adsorption kinetic model. On the contrary, TpStb-SO3Na presented low adsorption capacity for anionic dyes like methyl orange (MO) and fluorescein sodium (FS), rendering it a promising sorbent for the separation of cationic and anionic dyes based on charge difference. Furthermore, TpStb-SO3Na was easily regenerated and reused for five cycles with no obvious loss in its adsorption performance. This work uncovers the vast potential of anionic COFs for the effective removal of organic dye pollutants in wastewater.