Heteroporous bifluorenylidene-based covalent organic frameworks displaying exceptional dye adsorption behavior and high energy storage

Abstract

In this study we performed one-pot polycondensations of BFTB-4CHO with PyTA-4NH₂, BFTB-4NH₂, and BCTA-4NH₂ to prepare the bifluorenylidene-based covalent organic frameworks (COFs) BFTB–PyTA, BFTB–BFTB, and BFTB–BCTA, respectively. These three COFs possessed extremely high thermal stabilities, excellent crystallinities, and high specific surface areas. The BFTB–PyTA COF featured pores of a single size, whereas the BFTB–BFTB and BFTB–BCTA COFs had dual porosities. The COFs were exceptional adsorbers of the small dye molecule rhodamine B (RhB) in water; the maximum adsorption capacities reached as high as 2127 mg g⁻¹, outpacing those of all previously reported COFs, conjugated polymers, activated carbons, and other common nanoporous adsorbents. In addition, our COFs reached up to 99.2% of their maximum adsorption capabilities very rapidly (within 5 min). Furthermore, these COFs displayed good performance when used in electrodes for supercapacitors, with high stability after 2000 cycles. The superior adsorption efficiencies, ultrafast kinetics, and excellent reusability endow such COFs with tremendous potential for use as materials for removing RhB—and, presumably, other organic pollutants—from wastewater.