Selective recognition of MnO4− ion in aqueous solution based on fluorescence enhancement by surfactant capped naphthalene nanoparticles: Application to ultratrace determination of KMnO4 in treated drinking water

Fluorescent naphthalene nanoparticles stabilized and capped by CTAB prepared using reprecipitation method modifies surface to generate positive charge so as to attract electrostatically anionic analyte species. The dynamic light scattering studies used to check and select naphthalene nanoparticles of high stability and narrower particle size distribution. The scanning electron microscopy image showed spherical morphology of nanoparticles. The aqueous suspension of naphthalene nanoparticles exhibited red shifted intense, structureless emission from aggregates in comparison with the emission arising from dilute solution of naphthalene monomer in hexane. In anion recognition test based on fluorometry the aggregation induced emission found to be enhanced very significantly by MnO4− in comparison with oxidative anion Cr2O72− and Cr2O42−, while other anions responds oppositely and quenched the fluorescence. The straight line calibration curve of increase in fluorescence of naphthalene nanoparticles verses incremental amount of MnO4− solution obtained with correlation coefficient R2 = 0.989 is used further to develop fluorometric method of sensing and detection of KMnO4 solution from treated water samples. The mechanism of excited state charge transfer complex formation by electron transfer from Mn (II) to excited state naphthalene nanoparticles restricts vibrational motion and prevents nonradiative dissipation of energy, thus enhancing emission. The adsorption of MnO4− on surface of nanoparticles and excited state complexation between them is further evidenced by prolonged fluorescence lifetime of nanoparticles in presence of different amounts of MnO4− solution. The electrochemical studies showed surface adsorption of MnO4− and its subsequent redox type interaction with CTAB. The present fluorometric detection of MnO4− based on fluorescence enhancement of naphthalene nanoparticle probe is more sensitive, selective and simple.

Plausible mechanism based on excited state charge transfer complex formation between naphthalene nanoparticles and MnO4− ion.Figure optionsDownload as PowerPoint slide