Precise Fixation of the Spatial Configuration of Adsorption Groups for Removal of Mercury Ions from the Acidic Wastewater

Abstract Global release of up to 10 000 tons per year of mercury (Hg), the third most toxic ion, into the natural environment poses a significant threat to public health. However, conventional adsorbents with flexible adsorption sites have limited capability in mercury removal, especially in highly acidic and multiple competing ion environments. Herein, Hg(II) ion coordinated 3,3′,5,5′‐tetrabromo‐2,2′‐bithiophene is selected as the building monomer to construct the porous aromatic framework (PAF) through a Suzuki coupling reaction. The positions and angles of the two thiophene fragments are fixed by quadruple covalent bonds according to the coordination structure of the mercury ion. These covalently bounded bithiophene units exhibited ≈303% increased binding affinity and ≈140.0‐fold enhanced selectivity for Hg(II) ions, compared with flexible bithiophene moieties. In addition, the resulting solid (MILNU‐49) illustrates outstanding removal capability with a concentration varying from 5000.0 to 2.0 ppb, correspondingly, the removal efficiency is over 99.96% within 5 h from Hg(II) actual acidic wastewater. Remarkably, MILNU‐49 outperforms previously reported adsorbents for the adsorption of mercury ions under acidic conditions. The work enumerates a strategy for designing selective and high‐affinity binding sites, which are of great interest in the fields of environment, detection, and energy storage.