Temperature dependence on the size control of palladium nanoparticles by chemical reduction in nonionic surfactant/ionic liquid hybrid systems

Metal nanoparticles of palladium(Pd) were synthesized by the chemical reduction of palladium acetylacetonate (Pd (acac)(2)) dissolved in room-temperature ionic liquids (ILs) containing various nonionic Brij series surfactants (such as Brij-30, Brij-52, Brij-56, Brij-58, Brij-35, and Brij-700) and TX-100. The obtained self-assembled structure of Pd nanoparticles in the surfactant/IL hybrid systems without any cosurfactant/cosolvent was investigated using in situ small-angle X-ray scattering measurements and cryo transmission electron microscopy observations. Size control of Pd nanoparticles was accomplished by simply adjusting the reaction temperature to around 433 K and choosing the surfactant. Brij-58 and Brij-35 were the most appropriate of our experimental conditions for the formation of a stable surfactant/IL hybrid system containing Pd nanoparticles. The most efficient method to regulate Pd nanoparticle size was a temperature-controlled gradual synthesis whereby the reaction temperature for the reduction of Pd (II) ions was increased stepwise from 333 K to 433 K over approximately 60 min. Furthermore, the detailed formation mechanisms of the self-assembled structure of Pd nanoparticles in surfactant/IL hybrid systems were shown using in situ and time-resolved small-angle X-ray scattering measurements. (C) 2020 Elsevier B.V. All rights reserved.