Constructing bifunctional and robust covalent organic frameworks via three-component one-pot Doebner reaction for Cr(VI) removal

The integral part of covalent organic frameworks (COFs) is covalent bonds. Thus, stable and functional links must be developed to expand the potential applications of COFs. Herein, in situ linkage functionalization using a three-component irreversible Doebner reaction was achieved to fabricate chemically stable carboxylic acid-bearing COFs (Tp-Tta-COOH and Tp-Tapb-COOH), which have abundant chelating groups and ordered electron donor–acceptor moieties facilitating charge separation for effective Cr(VI) adsorption and photoreduction, respectively. These functionalized COFs are more effective at Cr(VI) removal via adsorption and photoreduction than their unfunctionalized counterparts (Tp-Tta and Tp-Tapb). The synergy of adsorption and photocatalysis is crucial to effectively remove Cr(VI) from aqueous solutions. This synergy empowers Tp-Tta-COOH to be used continuously for Cr(VI) removal without any elution after each cycle. Furthermore, Tp-Tta-COOH exhibits high chemical stability, durability, and recyclability. This study will promote the development of durable and useful COF materials for real-world applications.