Reversible transference of Au nanoparticles across the water and toluene interface: A Langmuir type adsorption mechanism

A novel method to reversibly modify the surface of gold nanoparticles is developed through electrostatic interaction between cationic tetraoctylammonium surfactant and anionic carboxylate groups. The particles can be extracted from the water phase into the toluene phase without aggregation after the adsorption of the surfactant on their surface. UV-visible spectroscopy reveals that a Langmuir type adsorption isotherm is observed during the transference process. The maximum adsorption amount of surfactants is equal to the total amount of carboxylate groups on the particle surface, indicating that the saturation adsorption behavior consistent with the;langmuir isotherm is solely caused by the 1:1 electrostatic charge interaction. Furthermore, through adjusting the dissociation states of carboxylate groups on the particle surface using hydrochloric acid, it is possible to redisperse the particles from toluene into the water layer because of the desorption of TOAB molecules from the particle surface. Studies using other methods such as infrared spectroscopy; energy-dispersive X-ray analysis, and transmission electron spectroscopy also support the above findings.