Detection and Removal of Mercury Ions in Water by a Covalent Organic Framework Rich in Sulfur and Nitrogen

Hg/Hg­(II) is deemed to be the most toxic heavy metal to humans. Therefore, designing suitable adsorbents to simultaneously achieve high capacity, rapid mercury adsorption, and fluorescence detection is still an important challenge in overcoming Hg²⁺ pollution. Here, we report a flexible alkylamine covalent organic framework (TpTSC), which has been used as an efficient adsorbent and achieves the dual-functional application of TpTSC for Hg²⁺, with a fluorescence detection limit of 2 ppm and simultaneously a removal capacity of 1035 mg g^–1. It can remove 10 ppm mercury solution to below 2 ppb (drinking water standard) within 10 min, and the removal rate is as high as 99.98%. To a certain extent, it exceeds the recently reported thioether or thiol functionalized adsorbents. The kinetic study shows that TpTSC displays a very high K_d value, with K_d = 1.2 × 10⁹ mL g^–1, which has a strong affinity for mercury. In addition, TpTSC displays a good recycling capacity, with a removal rate of over 90% after five cycles. In conclusion, sulfur modification is a useful strategy for developing dual-functional COFs to simultaneously remove and detect toxic heavy metal ions.