Series of Stable Anionic Lanthanide Metal–Organic Frameworks as a Platform for Pollutant Separation and Efficient Nanoparticle Catalysis

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.