Benzobisthiazole-bridged white fluorescent emitting covalent organic framework for simultaneous mercury detection and removal

Mercury (Hg2+), a heavy metal ion, is considered one of the most toxic metals on earth and is widespread as an environmental pollutant. Various promising adsorbents have been developed with accessible chelating sites and high affinity for heavy metal ions. Herein, we utilized the advantages of covalent organic frameworks (COFs) and designed benzobisthiazole-bridged (BBT) fluorescent COFs (FCOFs) for Hg2+ sensing applications. The BBT-FCOF nanosheets has a π-π transition, effective electron transfer, and enhanced delocalization within the π orbitals of the BBT ring. It emits a white fluorescence enabling real-time detection of Hg2+ metal ions. The excellent sensing property of BBT-FCOF nanosheets was attributed to the high sensitivity towards Hg2+; this was confirmed by the x-ray photoelectron spectroscopy binding energy of sulfur and nitrogen atom in BBT-FCOF. The limit of detection of Hg2+ was 30 ppb, which is very low compared to other published methods. ICP-mass measurement also proved that BBT-FCOF nanosheets removed almost 99% of Hg and BBT-FCOF distribution coefficient (Kd) was calculated to be 5 × 105 g−1. The recyclability test proved that HCl effectively removed the adsorbed Hg2+ metal ions from BBT-FCOF nanosheets, making it a useful tool for real-time Hg2+ detection and removal from waste water. [Display omitted] •Benzobisthiazole bridged fluorescent covalent organic framework was synthesized (BBT-FCOF) for sensing of Hg 2+.•BBT-FCOF highly selective towards toxic Hg2+ metal ion among other metal ion.•The LOD of BBT-FCOF towards Hg 2+ was about ≤30 ppb, and ICP-mass measurement confirmed 99% of Hg2+ removed from water.•The BBT-FCOF probe is stable in various pH and retain its Hg2+ sensing property.•The recycling test confirmed BBT-FCOF recovered 99% of its fluorescence.