Functionalization of UiO-66-NH2 with rhodanine via amidation: Towarding a robust adsorbent with dual coordination sites for selective capture of Ag(I) from wastewater

Selective capture and maximum recovery of Ag(I) from wastewater is of great significance for a sustainable future. In this work, novel rhodanine (Rd)-functionalized UiO-66 adsorbents (i.e., UiO-66-Rd and UiO-66-NH2-Rd) were designed and synthesized. Different from previously reported UiO-66 derivatives with single metal coordination sites, the as-synthesized UiO-66-Rd and UiO-66-NH2-Rd have dual coordination sites, resulting in higher capacity and outstanding selectivity. The maximum capacities of UiO-66-Rd and UiO-66-NH2-Rd are 112 and 163 mg.g(-1), nearly 5.6 and 8.2 times higher than that of UiO-66, respectively. Impressively, the maximum selectivity coefficient of UiO-66-NH2-Rd is approximately 1795 and 1173 folds higher than that of UiO-66 and UiO-66-NH2. The experimental characterizations and theoretical calculations indicate that the Rd-induced enhancement in the adsorptivity and selectivity are mainly attributed to the dual coordination sites (i.e., C-S and C=S bonds), which collectively coordinate with Ag(I) in the form of Ag mono-coordinated with S. Compared with the UiO-66-Rd, UiO-66-NH2-Rd possesses excellent recyclability and durability due to the vital role of amide bonds generated from -NH2 group in the functionalization of UiO-66 with Rd. Furthermore, UiO-66-NH2-Rd can almost completely remove Ag(I) from the actual wastewater with complex matrix, satisfying the national integrated wastewater discharge standard and industrial wastewater emission standard, highlighting a great potential of practical application.