Multifunctional Anionic Cyclotriphosphazene-Based Metal-Organic Framework Featuring a One-Dimensional Zn(II) Inorganic Building Unit for Selective Chemical Sensing and Efficient Photocatalytic Activity

Abstract

The anionic Zn(II)-based metal-organic framework (MOF), {[bisopibH2][Zn7(mu 9-L)2(mu 3-OH)2(mu-OH)2(H2O)2]6DMF} n (PCP-18), was successfully synthesized and structurally characterized using a cyclotriphosphazene-functionalized hexacarboxylate linker (H6L) in combination with a protonated imidazole-based ligand (bisopibH2+) serving as a charge-balancing cation. PCP-18 is a robust three-dimensional framework constructed from a one-dimensional Zn(II)-based inorganic building unit (IBU), in which Zn centers are connected through mu 2-OH and mu 3-OH bridges, and further extended by anionic hexacarboxylate linkers into a highly interconnected framework. PCP-18 displays remarkable fluorescence sensing efficiency toward hydroxylated nitroaromatic analytes, including 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2,4-dinitrophenol (DNP), and 1,3,5-trinitrophenol (TNP), with the ability to detect DNP at concentrations as low as 5.06 x 10-5 M, maintaining selectivity even under competitive conditions. Additionally, it demonstrates high sensitivity and selectivity for Fe3+ ions, with a detection limit reaching 5.58 x 10-5 M. Its semiconductive nature and anionic framework enable efficient photocatalytic degradation of cationic methylene blue (MB) with degradation efficiencies exceeding 90% under light irradiation, attributed to electrostatic interactions, ion charge effects, and a hole-mediated mechanism. The reusability of MOFs in photocatalytic applications underscores their stability and practical value. This study highlights PCP-18 as a versatile material for addressing critical environmental challenges, including pollutant degradation and hazardous compound detection, emphasizing its innovative and impactful contribution to MOF-based technologies for sustainable environmental remediation.