Thiol unit-functionalized ultrastable two-dimensional polymer for adsorption of palladium ions in a nitric acid medium

In contrast to the conventional postsynthetic oxidation process for constructing amide linkages, a two-dimensional (2D) polymer (DPA) platform with abundant amide-linkages was directly constructed in this study via a single step using the condensation reaction of trimesyl chloride and melamine. The subsequent postfunctionalization of the as-prepared platform was performed by further reacting it with cysteamine to form thiol units around the DPA platform. Next, the amide-linked thiol unit–functionalized 2D polymer (DPA-BGA) was applied in the selective adsorption of Pd(II) in a nitric acid medium. DPA-BGA exhibited high chemical stability when immersed in 3 M nitric acid for 24 h and high selectivity for Pd(II) over other 13 types of representative metal ions coexisting in the system. Furthermore, using X-ray photoelectron spectroscopy and density functional theory analyses, a plausible adsorption mechanism that involved the interactions between the thiol unit and Pd(II) was identified. Moreover, recycling experiments were performed to demonstrate the reusability of DPA-BGA, which could be used for at least four consecutive adsorption–desorption cycles without a considerable decrease in performance. This study provides a strategy for constructing a stable amide-linked 2D polymer platform and offers a method for its versatile functionalization for application in the field of nuclear research.