Waste‐to‐MOF: Upcycling of Waste Polyimide Into Europium‐Based Metal‐Organic Framework as Efficient Fluorescence Sensor of Biogenic Amines

ABSTRACT The fluorescence sensing method based on lanthanide metal–organic frameworks (Ln‐MOFs) offers high sensitivity, selectivity, and rapid, real‐time detection of biogenic amines (BAs). However, their high cost, complex synthesis, and unclear sensing mechanism limit practical application. Herein, waste polyimide is utilized as a precursor to synthesize Eu‐1,2,4,5‐benzenetetracarboxylic acid (Eu‐BTEC) via a two‐step hydrothermal–solution method. Under optimum conditions, the obtained Eu‐BTEC exhibits excellent fluorescence selectivity and sensitivity toward cadaverine, with an apparent constant of 1.58 ×10 6 L·mol −1 and a detection limit of 0.17 µmol·L −1 . Density functional theory calculations reveal that the amino groups of cadaverine donate electrons to Eu 3+ , blocking the intramolecular electron transfer from the benzene ligand to Eu 3+ . Owing to the absence of chromophores in cadaverine, this electron transfer leads to luminescence quenching of Eu‐BTEC. To achieve visual and portable detection, Eu‐BTEC‐based fluorescence test strips were fabricated by spraying its suspension onto filter paper, enabling visual quantification of cadaverine (0.50 µmol·L −1 ) under UV light. This study not only provides a sustainable route for converting waste polyimide into Ln‐MOFs but also elucidates the BA sensing mechanism through HOMO‐LUMO band‐gap and electron‐density analyses, offering new insights into the fluorescence quenching process of Ln‐MOFs.