Dual-Emission Metal–Organic Framework for Highly Selective Ratiometric Sensing of Lithium(I) Ions in Aqueous Solution

The development of highly selective and sensitive detection methods for lithium ions in various environments, such as aqueous or battery application, is highly sought. However, it remains elusive due to the small radius and weak coordination ability of lithium ions. Considering a metal–organic framework (MOF) possesses plentiful open coordination sites and an adjustable pore size, the well-designed MOF would be an ideal platform for the selective detection of Li + . Herein, a novel dual-emission luminescent metal–organic framework with three-dimensional structure, namely, Co–HIAT, was prepared by the hydrothermal method and structurally characterized. The Co–HIAT MOF displays the ligand-based emission at 340 nm and the charge transition emission between the metal ions and ligand at 410 nm simultaneously. Hence, the first example of ratiometric fluorescence detecting of Li + can be achieved by measuring the ratio of fluorescence at 410 to 340 nm in the fluorescent spectra of the Co–HIAT, which exhibits the outstanding sensitivity and selectivity, giving a detection limit down to 0.17 μM. Detailed experimental studies showed that the sensing mechanism involves the strong interactions of Li + with the reasonable hydroxyl and carboxyl oxygen atoms in the Co–HIAT framework, which is responsible for the ratiometric change in fluorescence emission properties in the inclusion of Li + . It is worth noting that electrochemical experiments further confirmed its superior affinity for lithium ions. This work represents an important and feasible pathway to design MOFs for the detection of Li + .