Space-resolved fluorescence properties of phenolphthalein-hydrotalcite nanocomposites

Phenolphthalein has been included into Zn–Al hydrotalcite-like compounds by taking advantage of the “memory effect” of hydrotalcites. In particular [Zn0.65Al0.35(OH)2] (CO3)0.1750.5H2O was calcined at 500 °C and the obtained mixture of Zn and Al oxides was dispersed in an aqueous alcohol solution containing 7 × 10−2 mol dm−3 phenolphthalein. The reconstruction of the layered hydrotalcite structure in the presence of the dye yielded formation of the composites in which phenolphthalein is intercalated in the interlayer region and/or adsorbed on the layer surface. Two samples were studied, the first, obtained at 25 °C, contained 0.17 mmol g−1 of phenolphthalein, mainly adsorbed on the surface, the second, obtained at 60 °C, contained 0.3 mmol g−1, in part intercalated. The samples were characterized by their X-ray diffraction patterns, specific surface areas and scanning electron micrographs. The photophysical characterisation of the bulk samples was based on the determination of their reflectance absorption and fluorescence spectra, the fluorescence lifetimes and fluorescence anisotropy. The results indicated different properties of the lowest singlet excited state of the adsorbed and intercalated dye. The space-resolved fluorescence images and fluorescence spectra obtained by confocal fluorescence spectroscopy of the two samples gave valuable information on the dye distribution and on the nature of the interactions between the dye and the inorganic matrix.