Selective and efficient detection of Pb2+ in aqueous solution by lanthanoid-organic frameworks bearing pyridine-3,4-dicarboxylic acid and glutaric acid

Optically-active luminescent materials based on lanthanoid ions attract significant attention due to their unique spectroscopic properties and the possibility of application as chemical sensors. Five isostructural lanthanoid metal organic frameworks, namely {[Pr(3,4-PDA)(Glu)(0.5)(H2O)(2)]CH3CN}(1) and [Ln(3,4-PDA) (Glu)(0.5)(H2O)(2)]: Ln = Nd (2), Sm (3), Eu (4), and Tb (5) (where 3,4-PDA = pyridine-3,4-dicarboxylic acid, Glu = glutaric acid), synthesized via the solvothermal method are reported. These lanthanoid metal-organic frameworks were characterized by FTIR, single-crystal X-ray diffraction, powder X-ray diffraction, BET, Hirshfeld surface analysis, DFT calculations, electronic spectroscopy, and photoluminescence techniques. MOFs 1-5 show porous two-dimensional (2D) structures. The luminescence properties of MOFs 4 and 5 demonstrated the range of sensing capabilities for some toxic heavy metals. However, MOFs 4 and 5 are highly sensitive for the detection of Pb2+, exhibiting the most effective luminescence quenching with the lowest detectable change in the signal occurring at similar to 0.014 and similar to 0.013 ppm of Pb2+ with MOFs 4 and 5, respectively, at room temperature in minutes. The MOF-based luminescence sensors designed in this paper demonstrate a successful and feasible strategy to use pyridine-3,4-dicarboxylic acid-based ligand as an antenna, which can efficiently sensitize Eu3+ and Tb3+ emission. MOFs 4 and 5 show great potential in the application of environmental detection of Pb2+ in water.

Automated summary

This study reports five isostructural lanthanoid metal organic frameworks as optically-active luminescent materials. MOFs 4 and 5 demonstrate highly effective luminescence quenching for the detection of toxic heavy metal Pb2+, with detectable changes in the signal occurring at concentrations as low as 0.014 ppm and 0.013 ppm of Pb2+, respectively, at room temperature in minutes.