A Dual-Functional Cyclophosphazene-Based Cu(II) Metal–Organic Framework for Photocatalytic Water Treatment and Efficient CO ₂ Separation

A copper(II)-based MOF, designated as PCP-7 and chemically formulated as ([Cu 2 (L)(H 2 O) 2 ]·2DMF), was synthesized using a nitrogen-rich cyclotriphosphazene-derived tetracarboxylate ligand ( H 4 L ). The three-dimensional framework, constructed from paddlewheel-type {Cu 2 (COO) 4 } secondary building units (SBUs), exhibited remarkable photocatalytic efficiency in the visible-light irradiation toward the degradation of organic dyes such as methylene blue (MB), rhodamine B (RhB), and methyl orange (MO). Detailed mechanistic investigations revealed that superoxide radicals (O 2 •– ) serve as the primary reactive species responsible for photocatalytic degradation. Under visible-light irradiation, PCP-7 achieved over 90% degradation efficiency of MB, RhB, and MO and maintained excellent structural stability over five consecutive cycles. Electrochemical analysis further confirmed its capacitive behavior, redox activity, and photoactive nature. Ideal Adsorbed Solution Theory (IAST) analysis revealed that PCP-7 exhibits favorable gas separation performance, achieving CO 2 /N 2 selectivity values of up to 41.9 at 298 K (and theoretically infinite at 323 K), together with a CO 2 /CH 4 selectivity of 29.4 at 273 K, underscoring its strong potential for efficient and selective CO 2 capture.