Fluoride sensing performance of fluorescent NH2-MIL-53(Al): 2D Nanosheets vs. 3D Bulk

Due to the ultra-thin morphology, larger specific surface area and more exposed active sites, two-dimensional (2D) metal-organic frameworks (MOFs) nanosheets can break the limitations of three-dimensional (3D) MOFs in sensitivity, response speed and the limit of detection for sensing application. In this work, fluorescent NH2-MIL-53(Al) nanosheets were developed as a fluoride detection sensor compared with the 3D bulk counterpart. The morphological and structural characteristics of the obtained products were systematically characterized, and the favourable chemical and fluorescent stability of NH2-MIL-53(Al) nanosheets were explored. Fluorescent NH2-MIL-53(Al) nanosheets showed high sensitivity, fast response speed (as short as 10 seconds), low limit of detection (15.2 ppb), wide linear detection range (5-250 µM), and all performances were better than that of its bulk counterpart. In addition, the sensing mechanism was investigated to be based on the transformation of NH2-MIL-53(Al) framework which induced the release of fluorescent ligands, resulting in an exceptionally enhanced fluorescence. This work highlights the advantages of 2D MOFs nanosheets in fluorescence sensing application.