Rare Earth complexes with dual functions for detecting Cu2+ ions and photocatalytic degradation of organic dyes: Synthesis, performance, and theoretical modeling

Abstract

In this study, four rare earth-based complexes [Sm(piac)₂(H₂O)₂]_n (1), [Gd(piac)₂(H₂O)₂]_n (2), [Tb(piac)₂(H₂O)₂]_n (3), and [Dy(piac)₂(H₂O)₂]_n (4) (where piac = 5-(1H-pyrazol-3-yl)isophthalic acid) were successfully synthesized using hydrothermal methods. All four complexes exhibited identical two-dimensional network structures. Among them, complexes 1, 3, and 4 demonstrated strong fluorescence properties, making them effective for detecting Cu²⁺ ions in water. The results revealed that these complexes effectively detected Cu²⁺ ions in water, with limits of detection (LOD) of 2.72 μM, 4.08 μM, and 1.93 μM, respectively. In addition, complexes 1–4 were utilized in the photocatalytic degradation of the organic dyes rhodamine B (RhB) and methyl orange (MO). Among them, complex 2 exhibited the highest catalytic efficiency, achieving 96.41 % degradation of RhB within 60 min and 90.11 % degradation of MO within 120 min. Electron paramagnetic resonance (EPR) spectroscopy confirmed that the primary reactive species involved in the photocatalytic degradation process were ·O₂^- and ·OH. Furthermore, density functional theory (DFT) calculations were conducted to analyze the frontier molecular orbitals, electrostatic potential, and density of states (DOS), offering valuable insights into the electronic structures, catalytic performance, and stability of the complexes.