Effective detection of Ag, Hg and dye adsorption properties studies of Ln-MOFs based on a benzimidazole carboxylic acid ligand.

Five new lanthanide metal-organic frameworks (Ln-MOFs), namely {[Ln(L)]·Cl}, [Ln = Pr(1), Nd(2), Eu(3), Ho(4), Ce(5)], based on a benzimidazole carboxylic acid ligand [HL = 2-(2-carboxyphenyl)-1-benzo[d]imidazole-6-carboxylic acid] were synthesized by a solvothermal method. Ln-MOFs 1-5 have the same two-dimensional layered structures. Interestingly, 1-5 exhibit excellent adsorption performance to anionic dye Congo red (CR), with adsorption capacities of 2724 mg g, 2719 mg g, 2718 mg g, 327 mg g, and 2273 mg g, respectively. Adsorption kinetics experiments showed that this kind of adsorption belonged to chemisorption; the hydrogen bonding and π-π interactions between the 1-5 host and CR guest molecules resulted in a high adsorption capacity. Luminescence and sensing experiments showed that 5 can be considered a promising multifunctional fluorescent sensor with good reusability and a high sensitivity toward Ag and Hg ions, with detection limits of 1.7 × 10 and 2.5 × 10 M, respectively.