Multifunctional Luminescent Eu(III)-Based Metal–Organic Framework for Sensing Methanol and Detection and Adsorption of Fe(III) Ions in Aqueous Solution

A novel lanthanide–organic framework (Eu–HODA), consisting of 2,2′,3,3′-oxidiphthalic acids as efficient sensitizing units, is assembled and characterized. Eu–HODA features rare chiral helical channels despite the achiral nature of H₄ODA. It is found that this MOF shows a unique luminescent response to methanol, in contrast to n-propanol and ethanol. Eu–HODA reveals a turn-off luminescence switching initiated by acetone molecules with an EC₅₀ of 0.03 vol %, which is below the occupational exposure limit of acetone stipulated by the American Conference of Governmental Industrial Hygienists. Furthermore, it also exhibits high sensitivity (Stern–Volmer constant K_SV = 2.09 × 10⁴ L/mol) and low detection limit (6.4 ppb) for Fe³⁺ ions in pure water because of the existence of uncoordinated carboxyl groups within open frameworks. Eu–HODA-based test paper provides a simple and reliable detection method for Fe³⁺ in practical applications.