Sulfur-Modified Flexible Covalent Triazine Polyamide (SF-CTPa) for Highly Selective Capture of Hg²⁺ in Aqueous Media

There are a number of sulfur-containing adsorbents that can trap Hg²⁺ in aqueous solutions with high selectivity. However, these adsorbents often require a large number of sulfur atoms in their structure. Additionally, the five- and six-membered ring structures are among the most stable. It would therefore be great to incorporate the stable five- and six-membered ring structures into covalent organic polymers (COPs), thus reducing the number of sulfur atoms required. In this study, we introduced a flexible structure to enhance the neighboring active sites more effectively. We termed the prepared adsorbent materials as sulfur-modified flexible covalent triazine polyamides (SF-CTPas). The adsorption of Hg²⁺ in water by SF-CTPa is a chemisorption process, with a maximum adsorption capacity of 1970 mg/g. Our experiments, characterizing the acid and alkali resistance, thermogravimetry, and cycle regeneration, show that SF-CTPa is a highly stable adsorption material. Meanwhile, the primary chelation mechanism of SF-CTPa for Hg²⁺ entails the stable six- and five-membered ring structures capturing the Hg²⁺ by means of flexible amides and adjacent nitrogen or sulfur atoms. Additionally, we placed the SF-CTPa with adsorbed Hg²⁺ in an aqueous solution for 7 days and found no Hg²⁺ in the solution.