Covalent organic polymers based on special dithioureas for efficient removal of Hg2+ from aqueous solutions

Abstract

The damage caused by mercury ions (Hg²⁺) to human beings motivates the development of highly efficient technologies for the removal of Hg²⁺ from water. Here, based on the coordination theory between functional groups and Hg²⁺, two covalent organic polymers (COPs) materials were successfully prepared by a more environmentally friendly Michael addition elimination reaction, and the thiourea structure, which has a particularly strong affinity for Hg²⁺, was successfully introduced into the material framework. The introduction of the special dithiourea structure created a rich environment of S and N atoms within the COPs structure, which exhibited high adsorption performance for Hg²⁺. Adsorption experiments showed that the dithiourea-functionalized COPs exhibited high adsorption capacities for Hg²⁺, with the maximum adsorption capacities of 840.9 and 880 mg g⁻¹ for the two materials, respectively. The adsorption performance remained relatively good after four adsorption-desorption cycles, and the adsorption selectivity for Hg²⁺ was intense. Mechanistic studies by X-ray photoelectron spectroscopy and density flooding theory calculations suggest that it is the S atoms within the structure that chelate with the Hg²⁺ and contribute to the adsorption capacity of the Hg²⁺. Therefore, this study provides a new strategy for the development of COP adsorbents for efficient removal of Hg²⁺ in aqueous solutions during remediation activities.