Post-modification of COFs by dimercaprol for adsorption and detection of trace Hg(II) in water

The key to removing and detecting trace Hg (II) in water is to achieve rapid adsorption and high adsorption capacity of the adsorbent while maintaining the simplicity and safety of the adsorbent preparation process. Herein, we report a post-modification of covalent organic frameworks by medical antidote dimercaprol (DMC-COF) for efficacious removing and detection on trace Hg (II) in water. The as-prepared DMC-COF showed excellent selectivity to trace Hg (II) and fast adsorption dynamics, which was attributed to the abundance of sulfhydryl and hydroxyl sorption sites in the COF mesopores and on the COF surface. The effluent concentration of Hg(II) coexisting with Ca(II) reduced from 30 μg·L −1 to the permissible limit (1 μg·L −1 ) of potable water standard within 30 s. The sorption equilibrium was achieved during 3 min and the adsorption rate reached over 98 %. The material also showed a wide applicable pH range (3.5–9.5), excellent regeneration feasibility and selectivity of Hg(II) coexisting with a wide range of heavy metals in tap water, and the effluent concentration of Hg(II) coexisting with trace of As(V), Cr(VI), Cd(II) and Pb(II) could reduce from 30 to 0.19 μg·L −1 during 10 min. Moreover, Hg(II) of 3, 6, 10 and 30 μg·L −1 in tap water could be achieved to meet the WHO standard within 1 min. Meanwhile, its conjugated framework could be used as a signal sensor for rapid testing for low concentration Hg(II) in water, with a fluorescence detection limit of 1.06 mg·L −1 . DFT calculations yielded the optimized structure of DMC grafted onto COF-V, revealing that Hg²⁺ and Hg(OH)₂ primarily adsorbed at the -S and -SH sites, predominantly through van der Waals interaction, whereas Hg(OH)⁺ mainly adsorbed at all the -S, -SH and -OH sites, governed by notable attraction.