Design and photocatalytic performance of Cd(II)-based coordination polymers for selective PNP degradation

In this study, two Cd(II)-based coordination polymers (CPs), [Cd(IPA)(Beib)]ₙ (1) and [Cd(PTA)(Beib)]ₙ (2), were designed and synthesized via a hydrothermal mixed-ligand strategy using isophthalic acid (H2IPA)/terephthalic acid (H2PTA) and 1,4-bis(2-ethylimidazol-1-yl)butane (Beib), aiming to develop efficient and selective photocatalysts for the degradation of p-nitrophenol (PNP). The structures and stabilities of the CPs were characterized by single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), Fourier-transform infrared (FT-IR) and thermogravimetric analysis (TGA). CP 1 forms a uncommon 3D 3-fold interpenetrated dmp framework based on 65·8 topology, and CP 2 displays a 3D 4-fold interpenetrated dia framework with 4-c (66) sqc6 topology framework. Photocatalytic performance studies reveal that under UV light irradiation, (1) achieves a high degradation efficiency of 83.56 % for PNP, significantly superior to (2) (69.68 %), and exhibits high selectivity toward PNP compared to other nitro compounds (e.g., TNP, MNP). Kinetic analysis indicates that PNP degradation follows a pseudo-first-order model with a rate constant of 0.01716 min⁻¹. Radical trapping experiments confirm that photogenerated holes (h⁺) and superoxide radicals (•O₂⁻) are the dominant reactive species. Additionally, (1) demonstrates stable catalytic activity in various water sources (deionized water, tap water, pond water) and maintains >90 % performance after five recycling cycles, with no obvious structural changes verified by PXRD. This work highlights the regulation of light absorption and charge separation efficiency of CPs through ligand engineering, providing a new strategy for designing highly selective photocatalysts for efficient degradation of nitro pollutants in the environment and demonstrating the application potential of CPs in wastewater treatment and environmental remediation.