Series of Stable Anionic Lanthanide Metal-Organic Frameworks as a Platform for Pollutant Separation and Efficient...

Eight new stable porous lanthanide metal-organic frameworks (Ln-OFs), namely, [Ln₂(BPTC)₂][(CH₃)₂NH₂]₂ [Ln = Ho (1), Eu (2), Gd (3), Dy (4), Er (5), Tm (6), Yb (7), Lu (8)], were prepared by 3,3',5,5'-biphenyltetracarboxylic acid (H₄BPTC) and lanthanide ions by solvothermal reactions. Complexes 1-8 show a three-dimensional (3D) 6,6-connected network {4¹²·6³}·{4⁸·6⁶·8} topology based on binuclear (Ln₂) clusters and feature a one-dimensional curving porous channel occupied by exchangeable dimethylamine cations ([(CH₃)₂NH₂]⁺) in the 3D anionic frameworks. The occupied [(CH₃)₂NH₂]⁺ in the anionic channels exhibited excellent ion-exchange ability, which is favorable to Pd²⁺ and cationic dye adsorption. Consequently, 1-8 were used to load Pd nanoparticles to catalyze the reduction of nitrophenols and adsorb and desorb methyl blue (MB). The catalytic reaction efficiencies of Pd@1-8 were higher than that of Pd/C (5 wt %) in the hydrogenation reaction of p-nitrophenol (p-NP). Moreover, Pd@1 exhibited good cycle stability and achieved nearly 100% p-NP conversion after eight cycles. Meanwhile, compound 1 also exhibited a high adsorption ability of MB, possessing an adsorption capacity of 1.41 g·g^-1 (second only to 1.49 g·g^-1 reported in the literature) selectively over rhodamine B (RhB) and methyl orange (MO) in aqueous solutions. Remarkably, the skeleton of 1 remained stable after four adsorption-desorption cycles of MB in aqueous solution.