Effective detection of Ag+, Hg2+ 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)]center dot Cl}(n), [Ln = Pr(1), Nd(2), Eu(3), Ho(4), Ce(5)], based on a benzimidazole carboxylic acid ligand [H2L = 2-(2-carboxyphenyl)-1H-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(-1), 2719 mg g(-1), 2718 mg g(-1), 327 mg g(-1), and 2273 mg g(-1), respectively. Adsorption kinetics experiments showed that this kind of adsorption belonged to chemisorption; the hydrogen bonding and pi-pi 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 Hg2+ ions, with detection limits of 1.7 x 10(-7) and 2.5 x 10(-6) M, respectively.