Photochemical synthesis of silver particles in Tween 20/water/ionic liquid microemulsions

Abstract

Metal particles of silver (Ag) were synthesized by the photoreduction of silver perchlorate (AgClO 4) in water-in-ionic liquid (ILs) microemulsions consisting of Tween 20, water and ionic liquids. The ILs were tetrafluoroborate anions associated with the cations 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF 4]) and 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF 4]). The time evolution of Ag particle formation by photoreduction using UV-irradiation was investigated by UV–Vis, cryo-TEM, extended X-ray absorption fine structure (EXAFS) and small angle X-ray scattering (SAXS) measurements. The average diameter of the metallic Ag particles prepared in the water-in-[BMIm][BF 4] and water-in-[OMIm][BF 4] microemulsions was estimated from TEM to be 8.9 and 4.9 nm, respectively, which was consistent with that obtained from the SAXS analysis. Using Guinier plots in a low q-range (<0.16 nm −1), we demonstrate that the average diameter of the water droplets that consisted of aggregates of ionic precursors of AgClO 4 before reduction and Ag particles after reduction, in the microemulsions, was estimated to be about 20–40 nm. The diameter of the water droplets increased as a function of photoreduction time because of the formation of Ag particles and their aggregates. EXAFS analysis indicated that Ag + ions were completely reduced to Ag 0 atoms during the photoreduction, followed by the formation of larger Ag particles.