Three-step stepwise adsorption of aqueous Hg²⁺ by highly selective mercury ion imprinted polymers with S/N bis-site:...

Efficient and selective removal of Hg²⁺ from Hg-contained wastewater remains a critical challenge in environmental remediation and advanced water treatment. In this study, a series of Hg²⁺-imprinted polymers were designed using bidentate S/N-coordinating allylthiourea (ATU) as the functional monomer. Different structural strategies were applied to enhance their selectivity and adsorption efficiency toward Hg²⁺. Comparative analysis of the structural features and adsorption behaviors of the polymers revealed effect of the imprinting effect and surface imprinting on Hg²⁺ capture. SEM and BET results demonstrated that ATU-IIP/SiO₂ possessed a higher specific surface area and a more open porous structure, which facilitated the full exposure of binding sites and significantly enhanced Hg²⁺ adsorption performance. Adsorption experiments showed that ATU-IIP/SiO₂ exhibited a rare stepwise adsorption process, with a twice the adsorption capacity that of ATU-IIP and reaching 70 % of equilibrium within 5 min. FTIR and XPS analyses identified S/N-containing groups (CSNH) dominated Hg²⁺ coordination. Density functional theory (DFT) calculations further confirmed the positive role of Hg²⁺ in promoting the transformation from CS to CS, supporting a dual-site synergistic coordination mechanism. Under coexisting ion interference, imprinted polymers achieved 84.3 % Hg²⁺ removal and maintained over 80 % recovery after five reuse cycles, while exhibiting over 99 % Hg²⁺ recovery from PVC industrial wastewater. This study provides new insights into the mechanisms of recognition, binding, and separation of Hg²⁺, offering a theoretical basis for its efficient removal from typical industrial wastewater.