Fluorescent Metal–Organic Framework MIL-53(Al) for Highly Selective and Sensitive Detection of Fe3+ in Aqueous Solution

Fluorescent metal–organic frameworks (MOFs) have received great attention in sensing application. Here, we report the exploration of fluorescent MIL-53(Al) for highly selective and sensitive detection of Fe3+ in aqueous solution. The cation exchange between Fe3+ and the framework metal ion Al3+ in MIL-53(Al) led to the quenching of the fluorescence of MIL-53(Al) due to the transformation of strong-fluorescent MIL-53(Al) to weak-fluorescent MIL-53(Fe), allowing highly selective and sensitive detection of Fe3+ in aqueous solution with a linear range of 3–200 μM and a detection limit of 0.9 μM. No interferences from 0.8 M Na+; 0.35 M K+; 11 mM Cu2+; 10 mM Ni2+; 6 mM Ca2+, Pb2+, and Al3+; 5.5 mM Mn2+; 5 mM Co2+ and Cr3+; 4 mM Hg2+, Cd2+, Zn2+, and Mg2+; 3 mM Fe2+; 0.8 M Cl–; 60 mM NO2– and NO3–; 10 mM HPO42–, H2PO4–, SO32–, SO42–, and HCOO–; 8 mM CO32–, HCO3–, and C2O42–; and 5 mM CH3COO– were found for the detection of 150 μM Fe3+. The possible mechanism for the quenching effect of Fe3+ on the fluorescence of MIL-53(Al) was elucidated by inductively coupled plasma-mass spectrometry, X-ray diffraction spectrometry, and Fourier transform infrared spectrometry. The specific cation exchange behavior between Fe3+ and the framework Al3+ along with the excellent stability of MIL-53(Al) allows highly selective and sensitive detection of Fe3+ in aqueous solution. The developed method was applied to the determination of Fe3+ in human urine samples with the quantitative spike recoveries from 98.2% to 106.2%.