Dual-functional metal–organic framework for efficient removal and fluorescent detection of perfluorooctanoic acid (PFOA) from water†
Abstract
Perfluorooctanoic acid (PFOA), a synthetic compound belonging to the per- and polyfluoroalkyl substances (PFAS) family, is notorious for its environmental persistence, bioaccumulation potential, and adverse health effects, posing a major challenge to environmental safety. Effective removal and detection of PFOA remains a challenge for conventional capture materials due to its unique molecular structure. In this study, we present a dual-functional metal–organic framework (MOF), UiO-66-N(CH3)3+, specifically designed for selective removal and detection of PFOA in water. This MOF is synthesized through the post-synthetic modification of UiO-66-NH2(Zr) with methyl iodide, introducing partially quaternized ammonium groups that enable ion-exchange functionality. The cationic ammonium groups significantly enhance electrostatic interaction with the anionic PFOA, leading to improved affinity and selectivity. As a result, UiO-66-N(CH3)3+ exhibits outstanding adsorption performance, achieving a high adsorption capacity of 1178 mg g−1 as estimated using the Langmuir isotherm model, along with over 99% removal efficiency within 5 minutes from a 50 ppb PFOA solution. Beyond its high sorption capability, the same MOF is also developed into a highly efficient fluorescence “turn-on” sensor for PFOA detection via a straightforward indicator displacement assay (IDA). In this approach, the MOF is initially loaded with the anionic dye sulforhodamine B (SRB), replacing the original iodide counterions. When bound within the MOF, SRB is nonfluorescent; however, upon exposure to PFOA, it is displaced and regains its strong fluorescence in solution. This rapid fluorescence “turn-on” response enables effective detection of PFOA with both high sensitivity and selectivity. The dual-functional MOF system described herein offers a promising strategy for the integrated detection and removal of PFOA from water, providing a simple yet powerful framework for designing multifunctional MOF-based adsorbents and sensors for PFAS pollutants.