Highly selective and sensitive detection towards cationic Cu2+ and Fe3+ contaminants via an In-MOF based dual-responsive fluorescence probe

Abstract Effective recognition and detection of heavy metal Cu2+ and Fe3+ ions from water are highly desirable because of their serious harms to human health and environmental safety. However, the existing detection techniques are still high cost, time-consuming and highly demanding for operators. As an alternative approach to address this issue, an indium-based MOF labeled as In-MOF of 1 with high water stability and opposite charges to Cu2+ and Fe3+ ions was successfully prepared and deployed as optical sensor to sense target analytes, according to our previous work. Prominently, this anionic framework exhibits high photoluminescence property and excellent fluorescence quenching response to target analytes with high selectivity, sensitivity and detection limits of 3.88 ppb for Cu2+, 4.2 ppb for Fe3+ ions, respectively, both of which have been confirmed to be ultro-low values among all reported MOFs-based photochemical sensors. Furthermore, the quick and accurate probing capability of 1 also has been proved even under the interference of dozens of anions or cations. The possible photoluminescence and fluorescence quenching mechanisms were studied in detail, revealing that rapid coordination reactions between free imidazole nitrogen and carboxyl oxygen atoms of the framework (Lewis basic sites) and the metal ions of Cu2+/Fe3+ (Lewis acid sites) should be proposed to be the key reason for high efficiency fluorescence quenching.