Rapid and solvent-free construction of S-rich covalent organic polymer for efficient removal of mercury

Abstract

Mercury (Hg(Ⅱ)) is an extremely hazardous heavy metal ubiquitously discovered in the global environment. Covalent organic polymers (COPs) have been recognized as promising adsorbents due to their exceptional properties tailored for Hg(II) sequestration. Nevertheless, the synthesis of the majority of COPs requires rigorous experimental conditions. Herein, a sulfur (S)-rich COP denoted as TpTU was successfully constructed using a solvent-free approach. Compared to TpUrea without S, TpTU exhibited superior Hg(Ⅱ) capture performance. The experimental results demonstrated splendid adsorption performance for Hg(Ⅱ) (187 mg·g−1), and the adsorption isotherm was well-fitted to the Freundlich model (R2 > 0.98). Meanwhile, adsorption equilibrium was achieved within 5 min, and thermodynamic analyses indicate that the adsorption process is endothermic in nature. In addition, TpTU exhibited exceptional selectivity for Hg(II) even in the presence of competing ions. The mechanism investment revealed that the incorporation of heteroatoms, particularly S and nitrogen (N), plays a critical role in enhancing the affinity of COP toward Hg(Ⅱ). Moreover, no significant loss is observed for its capacity even after eighth adsorption–desorption cycles, demonstrating remarkable reusability of TpTU. Furthermore, TpTU also achieved Hg(Ⅱ) removal efficiency of over 98.9 % in actual water samples. These results prove the practical potential of TpTU for the purification of Hg(II) polluted water, offering a promising avenue towards cleaner and safer water resources.