Europium Metal–Organic Framework Polymer Composites with Enhanced Luminescence and Selective Ferric Ion Sensing

Ferric ions (Fe3+) play an important role in various biological and chemical processes in living organisms, natural environments, and industry. To understand these roles, a fast and accurate sensor for the selective detection and quantification of Fe3+ is highly desirable. Herein, we report the development and assessment of a luminescent europium metal–organic framework (MOF, with specific acronym EuMTA, named for the ligand used in the synthesis: 2-methoxyterephthalic acid)─polymer composite material. Immobilizing EuMTA within a cross-linked poly(2-hydroxyethyl methacrylate) (PHEMA) matrix resulted in a significant enhancement in the ligand-Eu antenna effect, as well as an increase in the Fe3+ sensing range (detection of Fe3+ at concentrations between 2 and 120 ppm) compared to native EuMTA powder (0.16–4 ppm). The PHEMA matrix also functioned to protect the embedded MOF, improving the stability of the sensor under acidic conditions, while enhancing Fe3+ ion selectivity compared to a EuMTA powder suspension. The MOF-composite sensor exhibited excellent luminescence intensity, stability over prolonged storage (21 days), and reusability. Furthermore, the application of the MOF-composite sensor for mineral processing was successfully demonstrated by monitoring Fe3+ concentrations using a simulated mineral leaching model.