Cerium-based porous coordination polymers with hierarchical superstructures: fabrication, formation mechanism and their thermal conversion to hierarchical CeO2

Abstract

In this work, cerium-based porous coordination polymers (Ce-CPs) with hierarchical superstructures have been successfully synthesized on a large scale employing cerium nitrate as the metal salt and 2,5-pyridinedicarboxylic acid (2,5-H₂pdc) as the ligand by a mixed-solvothermal route. The as-obtained products were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetry and differential thermal analysis (TG-DTA). It was found that the hierarchical superstructures are composed of asymmetric branches with lengths ranging from 10 to 50 μm. The reaction parameters such as reaction temperature, total concentrations of the reactants, solvent composition, and the reaction time were investigated systematically. A possible formation mechanism for the hierarchical superstructures has been proposed to interpret the growth process. CeO₂ with similar hierarchical structures could be obtained after thermolysis of the Ce-CP precursors at 450 °C for 4 h. The UV-vis adsorption spectrum of the obtained CeO₂ shows that the band gap energy (E_g) is 2.64 eV, which is lower than that of bulk ceria. Moreover, the as-obtained CeO₂ also exhibited remarkable ability to remove rhodamine B (RhB).