Amino-Functionalized Metal-Organic Frameworks Nanoplates-Based Energy Transfer Probe for Highly Selective Fluorescence Detection of Free Chlorine

Novel highly fluorescent NH2-MIL-53(Al) was controllably synthesized by a facile one-step hydrothermal treatment of AlCl3·6H2O and NH2-H2BDC in water with urea as a modulator. The as-synthesized NH2-MIL-53(Al) nanoplates exhibited excellent water solubility and stability. In the present work, it can be found that strong fluorescence of NH2-MIL-53(Al) nanoplates was significantly suppressed after the addition of free chlorine, and a simple sensing system for fast, highly selective direct detection of free chlorine in water was established. Compared with other fluorescent sensors for free chlorine, the present methodology has a comparable detection limit of 0.04 μM (S/N = 3) and a wide detection range of 0.05 to 15 μM. On the other hand, the traditional redox-based fluorescent probes sharply suffered from the interference of MnO4–, Cr2O72–, and other oxidants with stronger oxidation capability than free chlorine while ours overcame this disadvantage. Further research suggests that it is more likely the energy transfer through N–H···O–Cl hydrogen bonding interaction between amino group and ClO– ions plays the key role in our system, providing a new and promising platform for free chlorine determination in water quality monitoring.