Studies of Selective Detection of Picric Acid in Solution Phase Using Fluorescent Polyphosphazene Nanofibers

The cyclomatrix-type polyphosphazene fluorescent nanofibers(PZS-NFs) were prepared by one-step precipitation polymerization of hexachlorocyclotriphosphazene and 4,4'-sulfonyldiphenol with trimethylamine as acid-accepter and a mixture of toluene and acetone (8:1 by volume) as solvent. The chemical structure, morphology, thermal stability, and fluorescent property of PZS-NFs, were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, thermal gravity analysis, and fluorescence spectroscopy, respectively. Then PZS-NFs were served as a fluorescent chemical sensor for the detection of PA in solution phase by a spectrofluorometric titration method using a spectrofluorometer. The selective detection performance was investigated, and the corresponding detection mechanism was also discussed. The results showed that the mean diameter of the nanofibers was 80 nm. The highly cross-linked and organic-inorganic hybrid structure endowed the nanofibers with excellent thermal stability. The initial thermal decomposition temperature was as high as 520 degrees C in nitrogen atmosphere. The nanofibers exhibited an intrinsically fluorescent emission at 433 nm when excited at 369 nm, and showed the fluorescence quenching response towards PA with high sensitivity, efficiency, and selectivity over a number of other analytes including 2, 4, 6-trinitrotoluene, 2, 4-dinitrotoluene, 1, 3-dinitrobenzene, 4-nitrophenol, nitrobenzene, 4-benzoquinone, chlorobenzene, and nitromethane in methanol. The quenching constant and detection limit for PA were 1. 81 x 10(4) M-1 and 80 mu g/L, respectively. The specific recognition of PA by PZS-NFs might be attributed to the effective enrichment of PA from solution to the surface of PZS-NFs realized by the acid-base interaction between the acidic phenolic hydroxyl groups of PA molecules and the electron-rich nitrogen atoms of the cyclotriphosphazene units in PZS-NFs, facilitating the formation of a ground-state non fluorescent complex of the nanofibers and PA as well as the excited-state energy transfer from the nanofibers to PA. Considering the simple preparation and high selectivity, PZS-NFs have a great potential to serve as a fluorescence chemical sensor for the detection of PA in practice.