Gold nanoparticles optical properties induced by water and an ionic liquid (bmimBF4) inside cationic reverse micelles

Abstract

Herein, we report the effect of a polar solvent entrapped in benzyl-n-hexadecyldimethylammonium chloride (BHDC) reverse micelles (RMs) as nanoreactors for the synthesis of gold nanoparticles (AuNPs). We evaluate how the room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF₄) and water inside the RMs could control the interactions at the interface as a key factor that affects the final properties of the synthesized nanoparticles. The results show that the bmimBF₄ supramolecular network under confinement plays an important role in the nucleation and growth mechanism of AuNPs. In addition, the results show how the polar solvent could induce a specific interaction at the interface, including ionic segregation, which affects the BHDC chloride (Cl⁻) counterion availability at the interface, droplet size, interface flexibility and thus the material exchange rate between droplets. These factors strongly influence the AuNPs size, polydispersity, morphology and crystallinity. The RTIL bmimBF₄ in BHDC RMs induces a decrease in ionic segregation of the Cl⁻ ions available at the interface which favors sphericity and monocrystallinity in the AuNPs formed. Moreover, water does not affect the availability of Cl⁻ ions at the interface, and the insertion of these ions in the previous crystalline layer is a key factor in the anisotropy and polycrystallinity of the AuNPs obtained. To the best of our knowledge, this is the first report to compare the influence of a polar solvent entrapped in BHDC RMs as nanoreactors for the synthesis of gold nanoparticles, and is also the first time bmimBF₄/BHDC/toluene RMs are used as reaction media for this particular reaction.