Post-modified ligand exchange of UiO-66 with high-exposure rhodanine sites for enhancing the rapid and selective capture of Ag(I) from wastewater

Abstract

Highly efficient capturing of silver from wastewater is critical for environmental and economic sustainability but remains significantly challenging to achieve fast kinetics and precise selectivity. Herein, we present two approaches based on rhodanine (Rd)-modified UiO-66 including post-modified ligand exchange for UiO-66-Rdp-m and in-situ solvothermal for UiO-66-Rdi-s. The resultant UiO-66-Rdp-m and UiO-66-Rdi-s perform maximum adsorption capacity of 120 and 109 mg·g−1, respectively, which are both about 6 times higher than pristine UiO-66. Benefitting from high-exposure Rd groups over the surface, UiO-66-Rdp-m exhibits about 3 times faster kinetic adsorption and nearly 15 times higher maximum selectivity coefficient than UiO-66-Rdi-s. Experiment and calculation demonstrate that the excellent performance of Rd-modified UiO-66 is dominantly owing to S chelation in the Rd group. In addition, site energy distributions of the Dubinin-Ashtakhov isotherm model confirm that UiO-66-Rdp-m has more effective sites for Ag(I) adsorption relative to UiO-66-Rdi-s. While a higher density of Rd outside the UiO-66-Rdp-m provides a larger coordination number of S/Ag (1.41) than UiO-66-Rdi-s (0.59), which is attributed to its sufficient exposed active S sites for multidentate coordination of Ag(I), thus significantly enhancing adsorption rate and selectivity. These findings are exploited to shed new insight into the design of adsorbents for the efficient recycling of noble metals from water.