A Schiff base-functionalized europium metal-organic framework for turn-off fluorescence sensing of Cu²

Developing a low-cost, highly sensitive, and accurate fluorescence-based approach for Cu²⁺ detection is crucial for reducing heavy metal pollution in industrial effluent. Here, we report a newly synthesized Schiff base europium metal-organic framework (Eu-MOF) and demonstrate its use for turn-off fluorescent detection of Cu²⁺. A Schiff base ligand derived from 2-aminoterephthalic acid and 2-hydroxynicotinaldehyde was coordinated with Eu³⁺ to construct the framework, enabling a simple and rapid sample pretreatment procedure. The material exhibited pH-dependent fluorescence behavior. With the concentration range of 2.5 to 500 mg L^-1, a linear response to Cu²⁺ was observed. The limit of quantification (LOQ) was 2.5 mg L^-1, while the limit of detection (LOD) was 0.83 mg L^-1. The method was effectively performed on vinegar, tea, fruit juice, and water samples, yielding spike recoveries of 84.5%-100.9% and relative standard deviations (RSDs) of 1.7%-4.8%. This method can be used to determine Cu²⁺ in various matrices.