Benzoisoquinoline-linked covalent organic framework via one-pot doebner reaction for high-efficiency removal of benzophenone-type UV filters: Dominance of donor–acceptor π–π stacking

A benzoisoquinoline-linked covalent organic framework (BIQ-COF) was synthesized via a one-pot Doebner reaction. • BIQ-COF displayed exceptional hydrolytic stability, enhanced hydrophilicity, and an electron-deficient π-system. • BIQ-COF exhibited the higher adsorption capacities toward benzophenone (BP)-type UV filters. • The donor–acceptor π–π stacking between BPs and the quinoline surface was the dominant driving force for adsorption. • The BIQ-COF exhibited the excellent chemical, thermal stability and good practicality. As typical emerging contaminants, benzophenone-type UV filters have attracted the growing concern owing to their widespread and persistent existence in aquatic environments, as well as their well-characterized endocrine-disrupting effects that pose significant risks to human health. Herein, a benzoisoquinoline-linked covalent organic framework (BIQ-COF) was synthesized via a one-pot Doebner reaction, in which reversible imine intermediates were converted into irreversible quinoline rings functionalized with electron-withdrawing carboxyl groups. This structural modification endowed the resultant framework with excellent hydrolytic stability, improved hydrophilicity, and an electron-deficient π-surface simultaneously. The synthesized BIQ-COF exhibited fast adsorption kinetics toward benzophenone-3 (BP-3), achieving equilibrium within 8 min. It also possessed a wide pH adaptability ranging from pH 3–10, and removal efficiency exceeding 95% in tap water, lake water, and river water matrices. Compared with the imine-linked covalent organic framework (IM-COF), BIQ-COF exhibited a remarkably higher adsorption capacity for all five tested benzophenone (BP) analogs. Systematic mechanistic investigations integrating experimental verification, electrostatic potential mapping, and force-field energy decomposition demonstrated that donor–acceptor π–π stacking between electron-rich aromatic moieties of BP molecules and the electron-deficient quinoline surface of BIQ-COF was the dominant driving force for adsorption, quantitatively contributing 74–89% to the total interaction energy. Two distinct interaction modes were further identified: BP analytes bearing –OCH 3 groups were adsorbed predominantly via π–π stacking, whereas –OH-functionalized BP analytes underwent a synergistic adsorption driven by both π–π stacking and hydrogen bonding. These results demonstrated that for electron-rich aromatic micropollutants, engineering π-electronic complementarity between the adsorbent framework and target contaminants is a more effective design strategy than optimizing hydrogen-bonding functional groups for improved adsorption performance. Download: Download high-res image (123KB) Download: Download full-size image