A Dual-Functional Cyclophosphazene-Based Cu(II) Metal-Organic Framework for Photocatalytic Water Treatment and Efficient CO₂ Separation

A Cu(II)-based MOF, denoted as PCP-7 and chemically formulated as ([Cu₂(L)(H₂O)₂]·2DMF), was synthesized using a nitrogen-rich cyclotriphosphazene-derived tetracarboxylate ligand (H₄L). The 3D porous architecture, constructed from paddlewheel-type {Cu₂(COO)₄} secondary building units (SBUs), exhibited remarkable photocatalytic efficiency in the visible-light-driven degradation of organic dyes such as methylene blue (MB), rhodamine B (RhB), and methyl orange (MO). Detailed mechanistic studies revealed that superoxide radicals (O₂•⁻) act as the primary active species during photocatalytic degradation. Photocatalytic tests achieved over 90% degradation of MB, RhB, and MO under visible light, with excellent stability over five cycles. Electrochemical analysis confirmed its capacitive behavior, redox activity, and semiconductive nature. Ideal Adsorbed Solution Theory (IAST) analysis revealed that PCP-7 exhibits favorable gas separation performance, achieving CO₂/N₂ selectivity values of up to 41.9 at 298 K (and theoretically infinite at 323 K), along with a CO₂/CH₄ selectivity of 29.4 at 273 K, underscoring its strong potential for efficient and selective CO₂ capture.