Bottom-up synthesis of a sulfhydryl-modified heteroporous covalent organic framework for ultrafast removal of trace Hg(Ⅱ) from water.

The development of functionalized covalent organic frameworks (COFs) is crucial in expanding their potential for removing toxic heavy metals from drinking water. Here, a new sulfhydryl-modified heteroporous COF (COFDBD-BTA) was prepared using a "bottom-up" approach in which a direct amine-aldehyde dehydration condensation between 2,5-diamino-1,4-benzenedithiol dihydrochloride (DBD) and [1,1'-biphenyl]-3,3',5,5'-tetracarbaldehyde (BTA) was occurred. The COFDBD-BTA featured a hexagonal kagome (kgm) structure and a sheet-like morphology. Notably, COFDBD-BTA contained densely S atoms that provided high-density Hg(II) adsorption sites for efficient and selective trace Hg(II) removal. COFDBD-BTA exhibited excellent performance in rapidly removing trace Hg(II) from 30 μg L-1 to 0.71 μg L-1 within 10 s, below the World Health Organization's allowable limit of 1 μg L-1. Additionally, COFDBD-BTA exhibited a high Hg (Ⅱ) removal level from water, achieving adsorption capacity of 687.38 mg g-1. Furthermore, the adsorbent exhibited a wide range of applicability for low concentration (6-500 μg L-1) Hg (Ⅱ), a simple and feasible regeneration method, and strong Hg(II) removal ability in real tap water systems. The excellent adsorption efficiency, outstanding recyclability, and one-step room temperature synthesis make S-rich COFDBD-BTA a promising candidate for eliminating Hg (Ⅱ) from drinking water.