Cationic Europium-Organic Framework for Chromatographic Column Separation of Ionic Dyes and Stimuli-Responsive Chromic Properties.

A novel 3D europium-based cationic framework (Eu-CMOF) has been constructed solvothermally by employing a viologen derivative as an organic functional building unit. Notably, Eu-CMOF demonstrates its capability as a proficient aqueous-phase ion-exchange host, facilitating the remarkable rapid chromatographic column separation of new coccine and malachite green (NC 3- /MG + ), as well as new coccine and methylene blue (NC 3- /MLB + ), in mere 2 to 4 min. Adsorption thermodynamics and kinetics of anionic dyes demonstrate that Eu-CMOF exhibits a higher adsorption capacity for NC 3- , as evaluated by the Langmuir model, reaching a value of 173 mg·g -1 . The pseudo-second-order rate constant is determined to be 3.84 × 10 -3 mg -1 ·g·min -1 . Additionally, Eu-CMOF displays reversible photochromic and amine- and ammonia-induced vapochromic behaviors. Further mechanistic studies reveal that these chromic behaviors are primarily attributed to the generation of free viologen radical stimulated by Xe-light or electron-rich amine/ammonia. This research contributes to the development of advanced materials with applications in rapid chromatographic separation and stimuli-responsive chromic properties, showcasing the potential of Eu-CMOF as a versatile platform for practical applications.