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

Abstract

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.