Glutathione-functionalized highly crystalline fluorescent covalent organic framework as a fluorescence-sensing and adsorption double platform for cationic dyes

Considering the high toxicity of cationic dyes to the environment and humans, the development of materials which possessed the function both of detection and adsorption of cationic dyes are of great significance. In this study, a novel glutathione (GSH)-functionalized highly crystalline fluorescent covalent organic framework (denoted as COF-TPDD-COOH), which can act as a fluorescence-sensing and adsorption double platform for cationic dyes, was fabricated reported for the first time. To effectively postsynthetically modification and form COF-TPDD-COOH, a fluorescent COF (namely COF-TPDD) with a high crystallinity was fabricated by optimizing a series of conditions affecting crystallinity. The as-prepared COF-TPDD-COOH exhibited good dispersion and outstanding fluorescence and adsorption performances, which yielded remarkable performances in the detection and enrichment of cationic dyes (malachite green, methylene blue and crystal violet). Low detection limits (LODs, 0.003–0.007 μg·mL−1) and high adsorption capacities (88.02–128.64 mg·g−1) were obtained for three cationic dyes. The introduction of GSH increased the possibility of COF-TPDD-COOH binding with cationic dyes, which further increased the enrichment effect of cationic dyes. After adsorption, the cationic dyes could more easily interact with COF-TPDD-COOH and capture the protons needed for fluorescence, thus destroying the excited-state intramolecular proton transfer effect and selectively quench the fluorescence. A sensing platform based on COF-TPDD-COOH was developed and applied for the detection and adsorption of three cationic dyes from real samples.