Fluorine-fluorine interaction-driven colorimetric sensor for PFOA-sensitive detection using F-functionalized Ce-UiO-66-NH MOF with oxidase-like activity.

A novel colorimetric sensor was designed for sensitive perfluorooctanoic acid (PFOA) detection based on a fluorine-functionalized Ce-metal-organic framework (F-Ce-UiO-66-NH) with oxidase-like activity, using 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. This F-Ce-UiO-66-NH was synthesized through ligand exchange and post-modification with pentafluorobenzaldehyde (PFBA) on the basis of Ce-terephthalic acid (Ce-UiO-66), incorporating pentafluorophenyl groups that enhance the material's affinity for PFOA, leading to a more sensitive absorbance change in the presence of PFOA. Experimental and computational assays revealed that oxidase-like activity of F-Ce-UiO-66-NH primarily arises from hydroxyl radicals (•OH) generated through the conversion of superoxide radicals (•O). Furthermore, PFOA molecules were shown to undergo self-aggregation on the F-Ce-UiO-66-NH surface via fluorine-fluorine (F-F) interactions between PFOA molecules and the pentafluorophenyl groups as well as between PFOA themselves, blocking the active Ce sites and hindering the interaction of O and TMB with F-Ce-UiO-66-NH, thereby diminishing its oxidase-like activity. Owing to these sophisticated mechanisms, this colorimetric sensor demonstrated a broad linear detection range from 0.5 to 210 µM with a low detection limit of 0.41 µM for PFOA, enabling precise quantification of PFOA concentrations in real environmental water samples. This work introduces a new strategy for constructing field-deployable colorimetric sensors based on F-F interaction, offering very valuable insights into the design and operational principle for PFAS detection.