Tailoring the pore architecture and crystalline structure of UiO-66 for the selective adsorption of anionic species in aqueous media

Abstract

Micropollutants such as organic dyes and pharmaceuticals have received much attention in recent years due to their harmful effects on humans and wildlife, high stability against natural degradation, and difficult removal in conventional water treatment plants. In this work, we have optimized the adsorption of organic pollutants on UiO-66 metal–organic frameworks by changing some synthesis parameters, which allowed the tuning of their crystal structure and pore architecture. Samples with an extended microporous structure and specific surface areas over 1300 m2.g−1 were prepared by a solvothermal approach, which favored the access of the pollutant molecules to active adsorption sites. The specific surface areas measured in this study are among the highest ever reported for UiO-66. In batch adsorption tests conducted using aqueous solutions containing low initial concentrations (20 mg.L-1) of acid orange (AO7), ibuprofen (IBU), and methylene blue (MB), the materials tested in this study exhibited preferential adsorption of the anionic species AO7 (192 mg.g−1) and IBU (173 mg.g−1), resulting in AO7/MB and IBU/MB selectivities of 9.6 and 8.7, respectively. The primary adsorption mechanism is most likely a combination of electrostatic and Lewis acid-base interactions involving Zr-(-SO3−) for AO7 and Zr-(–CO2−) for IBU. Subsequent tests with moderately higher concentrations of AO7 (50 mg.L–1) showed even higher adsorption capacities, exceeding 340 mg.g−1. These results demonstrate that the optimized UiO-66 structure prepared in this study exhibits high-performance adsorption capabilities for the removal of anionic pollutants from aqueous media, thereby expanding the knowledge on the use of Zr-based MOFs for water remediation.