Phase Transfer of Gold Nanoparticles across a Water/Oil Interface by Stoichiometric Ion-Pair Formation on Particle Surfaces

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Abstract
The transfer of surface-modified gold nanoparticles across a water/toluene interface was demonstrated. Stoichiometric ion-pair formation between carboxylate anions on particle surfaces and tetraoctylammonium cations brought about the phase transfer, and was revealed by transmission electron microscopy (TEM), IR, UV-vis absorption, and energy dispersive X-ray (EDX) spectroscopies. A surface structure of the transferred gold nanoparticles was also presented. During the nanoparticle transfer from water into an organic phase, an improvement in the dispersibility and a slight decrease in the average diameter were observed (3.6 → 2.9 nm) accompanied by a slight narrowing in the size distribution (standard deviation: 0.80 → 0.54 nm). The phenomena could lead to a new methodology for size and/or dispersibility selections.