Gold Nanorods as Nanoadmicelles: 1-Naphthol Partitioning into a Nanorod-Bound Surfactant Bilayer

As-prepared gold nanorods, stable in aqueous solution, bear a bilayer of the cationic surfactant cetyltrimethylammonium bromide (CTAB). This bilayer provides a ∼3 nm thick hydrophobic layer that could be used to sequester hydrophobic organic molecules from aqueous solution. We have investigated the uptake of 1-naphthol as a model hydrophobic compound by CTAB-coated gold nanorods using both ultraviolet−visible spectroscopy and gas chromatography with flame ionization detection. We find the adsorption isotherm of 1-naphthol partitioning into the CTAB bilayer on gold nanorods fits the Langmuir model. The maximum number of bound 1-naphthol molecules is 14.6 ± 2.2 × 103 molecules per gold nanorod, with an equilibrium binding constant of 1.97 ± 0.79 × 104 M−1 at room temperature.