An NH2-modified {Eu III2}–organic framework for the efficient chemical fixation of CO2 and highly selective sensing of 2,4,6-trinitrophenol

Abstract

In most instances, the incursion of functional groups on the inner surface of microporous MOFs could undoubtedly result in a significant improvement of their desirable performances, inspired by which one amino-functionalized ligand 2,6-di(3,5-dicarboxylphenyl)-4-aminobenzoic acid (H₅DDAC) was designed and synthesized. By employing H₅DDAC as the organic linker, the exquisite combination of dinuclear [Eu₂(CO₂)₉] and [Eu₂(CO₂)₆(H₂O)₂] generated one highly robust microporous framework of {(Me₂NH₂)₄[Eu₄(DDAC)₃(HCO₂)(OH₂)₂]·8DMF·9H₂O}_n (NUC-41), which was characterized by hierarchical channels and cage-like voids. Owing to the Lewis acid-base synergistic effect including open metal sites, free oxygen atoms and amino groups, NUC-41 with the aid of cocatalyst n-Bu₄NBr exhibited extremely high catalytic activity for the cycloaddition reactions of alkyl epoxides and CO₂ under mild solvent-free conditions, especially for epoxides with a smaller size. Furthermore, fluorescence experiments confirmed that the amino-functionalized skeleton of NUC-41 could effectively sense 2,4,6-trinitrophenol in aqueous solution over other nitro analytes including TNP, 2,4-DNP, 4-NP, 2,4-DNT, TNT, 1,4-DNB, 4-NT and NB with K_SV and the limit of detection being 8.6 × 10⁴ M⁻¹ and 3.5 × 10⁻⁶ M, respectively. Therefore, these results indicate that amino functionalization is an effective strategy to improve and expand the application performance of MOFs, which is critically related to the sustainable development of MOF research in this day and age.