Studied on highly sensitive fluorescent sensors for Fe3+, Nitrobenzene and dye adsorption properties of Ln-MOFs based on benzimidazole carboxylic acid ligand

Five new lanthanide metal-organic frameworks (Ln-MOFs) {[Ln(L)(H2O)5]·Cl}n (1–5), ([Ln=Pr(1), Nd(2), Eu(3), La(4), Ce(5)] based on benzimidazole carboxylic acid ligand [H2L = 2-(4-carboxyphenyl)-1H-benzo[d] imidazole-6-carboxylic acid]) with the same two-dimensional planar structure were synthesized by solvothermal method. Ln-MOFs 1–3 exhibited the good adsorption performance for the anionic dye Congo red (CR) and the adsorption capacities were 468, 449 and 438 mg·g−1, respectively. The adsorption kinetics indicated that the adsorption was chemical adsorption and the hydrogen bonds and π···π interactions between 1–3 hosts and CR guest molecules resulted in high adsorption capacities. Ln-MOFs 4 and 5 were developed for the exploration of fluorescence sensing performance. The results show that 4 and 5 can be used as fluorescent sensor for Fe3+ with good reusability, high sensitivity and selective detection, the detection limits were 1.1 × 10−5 and 4.3 × 10−6 M, respectively. Research shows that the quenching mechanism of Fe3+belongs to fluorescence resonance energy transfer (FRET). Meanwhile, 4 and 5 also have good detection effect on nitrobenzene (NB) and the detection limits were 1.6 × 10−6 and 2.4 × 10−7 M, respectively.