S,N-rich luminous covalent organic frameworks for Hg2+ detection and removal

The challenge for simultaneous detection and removal of Hg2+ is the design of bifunctional materials bearing abundant accessible chelating sites with high affinity. Covalent-organic frameworks (COFs) are attracting more and more attention as potential bifunctional materials for Hg2+ detection due to their large specific surface area, ordered pores, and abundant chelating sites. Here, a new luminous S,N-rich COFBTT-AMPD based on hydrophilic block unit of 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AMPD) was constructed, which improved the solubility and affinity for Hg2+ greatly. Another S-rich fused-ring unit of benzotrithiophene tricarbalaldehyde (BTT) enhanced the conjugation of COFBTT-AMPD, and the methyl-rich chains block unit of AMPD effectively suppressed the aggregation-caused quenching. Thus, the COFBTT-AMPD emitted strong fluorescence at 546 nm in liquid and solid as well as different solvent with a wide pH range, which was used for the visual detection and removal of Hg2+ (detection limit: 2.6 nM, linear range: 8.6 × 10−3-20 μM, monolayer adsorption capacity: 476.19 mg g−1) successfully. COFBTT-AMPD-based fabric and light-emitting diode coatings were further constructed to realize the visual detection of Hg2+ vapor. The results reveal the potential of S,N-rich luminous COFBTT-AMPD for Hg2+ detection and remediation in the environment.