Post-synthetic modification of a covalent organic framework via a thiol–ene reaction for improving fluorescence detection and removal of cationic crystal violet carcinogenic dye†

Abstract

Crystal violet (CV) as a cationic dye shows both biological toxicity and strong visual contamination. Therefore, the detection and removal of CV are essential for the ecosystem and human health. Unfortunately, most studies on this have been discrete, making it difficult to combine detection and removal in a single material. Herein, we have used 2-mercaptoacetic acid via the thiol–ene reaction for the first time to graft a carboxyl group onto a covalent organic framework (COF-A), which is capable of fluorescence detection, greatly improving the removal of CV from aqueous solution. Surprisingly, the modification also slightly improves the fluorescence detection ability. Compared with COF-A, the detection limit of COF-S-COOH for CV decreased from 0.089 to 0.030 μM, while the removal rate was enhanced to >99% at a concentration less than 20 mg mL⁻¹. Meanwhile, COF-S-COOH has good cycling ability in both functions. These phenomena are demonstrated by instrumental characterization and theoretical calculations, revealing fluorescence quenching induced by IFE and FRET and removal effects induced by electrostatic gravity, hydrogen bonding and π–π stacking. In this paper, we provide a new modification strategy for COF-A to achieve a bifunctional combination of detection and adsorption of CV.