A novel hydroxyl-riched covalent organic framework as an advanced adsorbent for the adsorption of anionic azo dyes

Considering the highly carcinogenic and mutagenic of anionic azo dyes to the environment and humans, the development of high efficiency adsorbent for them are of great significance. In this study, a novel hydroxyl-riched covalent organic framework (denoted as COF-OH), which can act as an advance adsorbent for anionic azo dyes, was fabricated for the first time. The as-prepared COF-OH demonstrated good dispersion in water, remarkable adsorption performances and good selectivity for anionic azo dyes including eriochrome black T, eriochrome blue black R and congo red. The adsorption capacities of them ranged from 90.71 to 229.12 mg g^-1, and the extraction efficiencies of them (>75.91%) were much higher than other dyes (e.g. Methylene blue, direct red 80, 1.46%-39.57%). By optimizing the adsorption conditions (adsorbent dosage, adsorption time, pH, and salt concentration) and desorption conditions (desorption solvent, desorption time and desorption frequency), a dispersive micro solid-phase extraction (D-μ-SPE) method was developed. Further, coupled D-μ-SPE with HPLC-PDA analysis, an effective method was fabricated for the extraction and detection of three selected dyes. The method showed good linearity in the range of 0.1-200 μg mL^-1 (R² > 0.9966), low limits of quantification (0.10 μg mL^-1-2.00 μg mL^-1), low limits of detection (0.03-1.50 μg mL^-1) and good precision. Finally, the COF-OH based D-μ-SPE was successfully applied to extract three selected dyes from water samples (recoveries ranged from 73.90 to 104.00%) and congo red from beverages (recoveries ranged from 81.40 to 111.80%). Besides, by using computer simulation, FT-IR and UV-vis analysis, the adsorption mechanisms of COF-OH to three selected dyes were explored preliminarily.