Novel Sulfhydryl Functionalized Covalent Organic Frameworks for Ultra-trace Hg2+ Removal from Aqueous Solution

Abstract Two kinds of novel sulfhydryl functionalized covalent organic frameworks were fabricated as adsorbents for the removal of ultra-trace concentrations of Hg2+ from water. The two kinds of sulfhydryl functionalized covalent organic frameworks were obtained via a thiol-ene click reaction between the thiol groups of trithiocyanuric acid (TTC) or bismuththiol (BMT) and vinyl groups on the surface of covalent organic frameworks. The material structure was characterized by XRD, SEM, EDS, FT-IR, BET, and TG analysis. Due to their rich sulfur content, both adsorbents (COF-SH-1 and COF-SH-2) exhibited a high level of selective Hg2+ removal from aqueous solution with maximum adsorption capacities of 763.4 mg g−1 and 526.3 mg g−1, respectively. Furthermore, in the presence of ultra-low concentrations of Hg2+ both materials exhibited excellent performance, achieving rapid Hg2+ removal at concentrations from 10 μg L−1 to less than 0.02 ng L−1. Analysis of the adsorption mechanism indicates that the sulfur containing chelating groups exhibit a strong binding capacity for Hg2+. Results show that the structure determines the performance, with the amount of adsorption sites being related to the adsorption capacity. Therefore, as sulfhydryl functionalized covalent organic frameworks contain an abundance of adsorption sites, these materials can effectively achieve the removal of ultra-low trace Hg2+ concentrations and have promising future application potential for the environmental detection of heavy metals.