A self-assembled metal-organic framework for enhanced UO fluorescence sensing: integration of an octa-nuclear zinc cluster with hexakis(4-carboxyphenoxy)cyclotriphosphazene

• Published in: CrystEngComm 2024-06, Vol.26 (25), p.3341-3348
• Main Authors: Chen, Xi, Chen, Zi-tong, Xu, Shi-xian, Chen, Yuan, Tong, Jia-ping, Li, Bao
• Format: Article
• ISSN: 1466-8033
• DOI: 10.1039/d4ce00401a

A novel metal-organic framework based on octa-nuclear zinc clusters, namely [Zn 4 (L)(OH) 2 (H 2 O) 4 ] (Zn-MOF) (H 6 L = hexakis(4-carboxylatophenoxy)cyclotriphosphazene), has been synthesized and structurally characterized by a solvothermal method. Single-crystal X-ray diffraction shows that eight zinc ions form a linear octa-nuclear cluster via a μ 3 -OH group, and each hexakis(4-carboxylatophenoxy)-cyclotriphosphazene connects four octa-nuclear clusters to construct 3D frameworks with one-dimensional pore structures. Zn-MOF exhibits suitable fluorescence properties, water stability as well as thermal stability, and can be applied as a convenient fluorescent probe for the detection of radioactive uranyl cations (UO 2 2+ ) and ferric ions (Fe 3+ ) through fluorescence quenching behavior. The corresponding K sv values can reach 7.44 × 10 3 M −1 and 1.49 × 10 4 M −1 . Meanwhile, the theoretical calculations fully indicated that the introduction of UO 2 2+ effectively inhibited the metal-to-ligand charge transfer (MLCT) of Zn-MOF, which in turn led to the fluorescence quenching phenomenon. Therefore, Zn-MOF prepared using crystal engineering can be used to construct an efficient and reliable fluorescent probe used in the fields of environmental monitoring and nuclear waste treatment. A novel photoactive Zn-MOF was successfully synthesised by introducing a flexible cyclotriphosphonitrile hexacarboxylic acid, which achieves a sensitive fluorescence quenching response to radioactive UO 2 2+ ions and the heavy metal Fe 3+ .