Catalytic Activity of Zn(II) Coordination Polymer Based on a Cyclotriphosphazene-Functionalized Ligand for Removal of Organic Dyes

The 3D Zn(II) coordination polymer {[Zn₃(L)(4,4′-bpy)]}_n (GTU-3) was prepared with a novel hexapod-shaped molecular building block, hexakis(methyl-2-(4-phenoxyphenyl)acetatebenzene) cyclotriphosphazene (H₆L₁) by solvothermal reaction in dimethylformamide (DMF). Zn(II) coordination polymer was characterized by FTIR, thermal analysis, SEM-EDX, BET, powder X-ray diffraction analysis, and single crystal X-ray diffraction techniques. GTU-3 consists of six crystallographically independent Zn²⁺ ions, two fully deprotonated cyclophosphazene-based ligands, and two 4,4′-bipyridines (4,4′-bpy). In the complex, the flexible multisite cyclotriphosphazene bridging ligand (H₆L) was completely deprotonated. GTU-3 exhibited relatively good catalytic activity toward Rhodamine B (RhB) removal in aqueous solution. A 0.4 g/L amount of GTU-3 could degrade the 10 mg/L solution of RhB up to 76.5% in the presence of peroxymonosulfate (PMS) oxidant in 1 h. The kinetic studies showed that the degradation process followed pseudo-first-order kinetic. By extending the degradation time to 5 h, the degradation efficiency reached 95.3%. Under the same conditions, Methylene Blue (MB) and Acid Red 17 (AR17) dyes were degraded by 86.2% and 52.8%, respectively.