Ln-MOFs with window-shaped channels based on triazine tricarboxylic acid as a linker for the highly efficient capture of cationic dyes and iodine

Abstract

Exploring the adsorption of small molecules, such as dyes and iodine, by using novel functionalized MOFs has aroused widespread interest. In this work, seven isostructural compounds were synthesized successfully under solvothermal condition, namely [Ln₂(TATAB)₂]·xDMF·yH₂O (1–7; Ln = Eu³⁺, Gd³⁺, Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺ and Y³⁺), by the reaction of 4,4′,4′′-((1,3,5-triazine-2,4,6-triyl)tri(azanediyl))tribenzoic acid (H₃TATAB) and rare earth metal ions. X-Ray diffraction analysis revealed that a window-shaped 3D structure was formed by “paddle wheel”-type [Ln₂(CO₂)₆] secondary structural units connected to eight H₃TATAB ligands, in which the channel size reached 2.73 nm and the available volumes of all the compounds surpassed 61%. Considering such large porosity and the π-electron walls of TATAB³⁻, the adsorption performance of 1 as a representative for five kinds of dyes in aqueous solution and iodine in cyclohexane solution were studied. Interestingly, 1 displayed a highly sensitive and selective adsorption behaviour to the cationic dye methylene blue (MB). Moreover, the iodine-adsorption experimental results demonstrated that 1 had a reversible adsorption effect on iodine with an adsorption capacity of 758.72 mg·g⁻¹.