Selective detection of Cr(III) among various chromium oxidation states in aqueous environments

Chromium (III), as a significant environmental pollutant, poses a serious threat to human health when accumulated in excess, making it imperative to develop highly sensitive and rapid on-site detection methods. In this study, a Eu³⁺-based metal-organic framework (MOF) was successfully synthesized using a dual-ligand strategy, enabling ratiometric fluorescence detection of Cr(III). During the detection process, distinct changes in the fluorescence ratio were observed, accompanied by a notable color shift from red to blue, providing a clear visual cue. Aromatic π-conjugated organic ligands were selected to enhance the photoluminescence properties, while a second ligand was introduced to optimize the crystal size and pore structure of the MOF. The experimental results demonstrated that the MOF material exhibited outstanding ratiometric fluorescence properties for Cr(III) detection, with high stability. Additionally, the material showed excellent selectivity, anti-interference ability, and sensitivity for detecting Cr(III) in water environments, with a detection range of 0-24 μM and detection limit as low as 59 nM. Further investigation revealed that the changes in ratiometric fluorescence signals were induced by Cr(III)-specific partial collapse of the crystal structure and ligand release. Finally, a MOF-based test strip was developed, where the vivid fluorescence color changes enabled visual detection by the naked eye. The test strip also demonstrated good recovery efficiency in real water samples, further confirming the material's potential as a real-time smart sensor for Cr(III) detection.