Structural and Optical Properties of Novel Surfactant Coated TiO₂–Ag Based Nanoparticles

Abstract

Stable dispersions of surfactant-coated TiO₂–Ag based nanoparticles in apolar medium have been prepared by performing sequentially the hydrolysis of titanium(IV) isopropoxide and the reduction of Ag⁺ in the confined space of sodium bis(2-ethylhexyl)sulfosuccinate (NaAOT) reverse micelles. Depending on the sequence length, this novel procedure allowed the synthesis of semiconductor–metal nanoparticles, nominally indicated as TiO₂/Ag, TiO₂/Ag/TiO₂, and TiO₂/Ag/TiO₂/Ag, stabilized by a monolayer of oriented surfactant molecules. The structural characterization of these nanoparticles has been performed by High Resolution Transmission Electron Microscopy (HR-TEM), while optical properties were investigated by UV–Vis absorption and fluorescence spectroscopies. TEM investigation showed the presence of globular nanoparticles with an average diameter of about 10 nm composed by distinct amorphous TiO₂ and crystalline Ag glued domains whose structure depends on the sequence length. UV–Vis absorption measurements highlighted the mutual metal–semiconductor influence on the TiO₂ energy band gap and on the Ag plasmon resonance. Steady-state fluorescence spectra analysis allowed to reveal the strong inhibition of the electron–hole radiative recombination in the TiO₂ domains due to the Ag and the appearance of a new emission band centred in the 484–545 nm range. Possible attributions of the involved electronic transition of this last emission are discussed.