A Simple Synthesis Method for Gold Nano- and Microplate Fabrication Using a Tree-Type Multiple-Amine Head Surfactant

In this paper, a single tree-type multiple-head surfactant, bis (amidoethyl-carbamoylethyl) octadecylamine (C18N3), which functions as both the reducing and capping agent in the reaction system, has been used to fabricate gold nano- and microplates. The triangle and hexagonal plate, polyhedron, and sphere morphology of the gold nanoparticles could be easily controlled simply by changing the molar ratio of C18N3/HAuCl4. Other influences on the morphology of the gold particles, such as Cl− concentration, temperature and time, were also studied. At standard conditions, 80 °C, and a molar ratio C18N3/HAuCl4 of 6.9 in a 0.5 M KCl aqueous solution, the size of the plates could be manipulated from several tens of nanometers to several micrometers just by changing the C18N3 concentration. A crystalline growth process for the nanoplate formation has been observed in this system. At the initiation of the crystalline formation, the predominant morphology was triangular, followed by a mixture of triangular, hexagonal, and truncated triangular structures as the particle grew larger. Ultimately, the structures became primarily hexagonal. As-prepared gold nano- and microplates greatly enhanced the surface enhanced Raman scattering (SERS) of ascorbic acid molecules compared to that of other gold nanoparticle morphologies.