Bipyridine-Functionalized Cd(II) Coordination Frameworks Based on Robust Cyclophosphazenes: Structural Engineering toward Enhanced Photocatalytic Activity

Abstract

Three Cd(II)-based coordination polymers were constructed using the 2,2′-bipyridine (bpy) ligand, alongside cyclotriphosphazene-functionalized multicarboxylates (L1, L2, and L3), which were carefully optimized to yield a 2D layered architectures (PCP-11 and PCP-13) and a 1D polymeric chain structure (PCP-12). The coordination polymers were synthesized via solvothermal methods and comprehensively characterized by PXRD, SCXRD, and TGA. All PCPs exhibited high photocatalytic activity, achieving up to 90% degradation of organic dyes such as MB, MO, and RhB. Among them, PCP-12 exhibited the highest performance, which is attributed to its binaphthoxy-substituted ligand, lower band gap, and the strong π···π stacking interactions between the 1D chains. Mechanistic studies revealed that superoxide radicals (O₂•⁻) were the primary ROS (reactive oxygen species) responsible for dye degradation. PCP-12 maintained high efficiency over multiple cycles due to its excellent reusability, efficient charge transport, and favorable band structure. PCPs show great potential as photocatalysts, with performance governed by their composition and structure.