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.