4 in 1: multifunctional europium–organic frameworks with luminescence sensing properties, white light emission, proton conductivity and reverse acetylene–carbon dioxide adsorption selectivity

Abstract

Lanthanide metal–organic frameworks (Ln-MOFs) combine the lanthanide luminescence characteristics and the advantages of porous materials, which can be used in various research fields by exploring their multifunctional properties. A three-dimensional water-stable and high-temperature resistant Eu-MOF [Eu(H₂O)(HL)]·0.5MeCN·0.25H₂O (H₄L = 4-(3,5-dicarboxyphenoxy)isophthalic acid), demonstrating a high photoluminescence quantum yield, was synthesized and structurally characterized. In terms of luminescence, the Eu-MOF exhibits excellent selectivity and quenching sensing for Fe³⁺ (LOD = 4.32 μM) and ofloxacin, as well as color modulation with Tb³⁺ and La³⁺ to develop white LED components with high illumination efficiency (color rendering index, CRI = 90). On the other hand, narrow one-dimensional channels of the Eu-MOF decorated with COOH groups enable a rare reverse adsorption selectivity in a CO₂/C₂H₂ gas mixture. In addition, the protonated carboxyl groups in the Eu-MOF provide an efficient conducting platform for proton transfer with a conductivity value of 8 × 10⁻⁴ S cm⁻¹ at 50 °C and RH 100%.