A water-stable Eu-MOF for highly selective and visual detection of Fe3+ in aqueous media

The pursuit of luminescent metal–organic frameworks (MOFs) as functional materials for aqueous phase sensing continues to grow. In this work, a new water-stable Eu-MOF (1) has been successfully obtained using a bifunctional ligand bearing both carboxylate and tetrazole groups. Single-crystal structure analysis reveals a nine-coordinate Eu3+ center with a monocapped square antiprismatic coordination environment, while the tetrazole units remain non-coordinating and participate in hydrogen-bonding contacts. 1 shows good thermal robustness and bright Eu3+-centered luminescence (Φ = 7%, τ = 185 µs). Luminescence measurements demonstrate that 1 can selectively and sensitively detect Fe3+ in aqueous solution, with quenching attributed to competitive absorption. A convenient membrane-based test strip was also constructed for naked-eye visual sensing. This study offers a viable strategy for developing MOF-based optical sensors for environmental monitoring. A water-stable Eu-MOF serves as a highly selective luminescent sensor for Fe3+ ions, enabling visual detection via a portable composite membrane.