The role of Fe3+ ions in fluorescence detection of H2S by a bimetallic metal-organic framework

A novel bimetallic MOF (i.e., FexAl1-x-MIL) with fluorescence quenching in the probe, was constructed to detect H2S based on a “turn-on” effect in an aqueous system. Interestingly, a trace amount of Al3+ replaced by Fe3+ in the parent MOF Al-MIL-53-NH2 causes significant fluorescence quenching in the bimetallic MOF, which is attributed to the strong ligand to metal charge transfer between unpaired electrons in Fe3+ and π-conjugated BDC-NH2 ligands. After H2S treatment, a fluorescence augmentation was observed, with a good linear relationship between H2S concentration (0–38.46 ​μM) and fluorescence intensity, indicating that Fe0.05Al0.95-MIL could be used for quantitative H2S detection. Particularly, Fe3+ in the bimetallic MOF seized by S2− facilitated the partial degradation and subsequent release of BDC-NH2 ligands, which were determined to be real fluorophores that contributed to the fluorescence enhancement. This study offers new insights into the luminescent bimetallic MOF design and would expand its application in chemical sensing. A novel bimetallic MOF FexAl1-x-MIL was successfully synthesized, which can be used to detect H2S based on a fluorescence “turn-on” effect in an aqueous system. The fluorophores were identified to be the released BDC-NH2 linkers from the decomposition of bimetallic MOF during the H2S sensing process. [Display omitted] •A novel bimetallic MOF (i.e., FexAl1-x-MIL) enables H2S detection in water based on a fluorescence “turn-on” strategy.•Incorporation of secondary Fe3+ ions within parent MOF Al-MIL-53-NH2 caused significant fluorescence quenching in probe.•Partial decomposition of bimetallic MOF occurred during H2S treatment because of ultrahigh affinity between Fe3+ and S2−.•BDC-NH2 released in the solution were identified to be real fluorophores that contributed to the fluorescence enhancement.