Facile synthesis of two-dimensional highly branched gold nanostructures in aqueous solutions of cationic gemini surfactant

Abstract

Snowflake-like two-dimensional highly branched gold nanostructures (2DHBNs) have been constructed in the presence of hexamethylene-1,6-bis (dodecyl dimethylammonium bromide) (C₁₂C₆C₁₂Br₂) through the reduction of HAuCl₄ by ascorbic acid. High resolution transmission electron microscopy results indicate that the 2DHBNs are uniform in crystallographic orientation, where the branched nanostructures grow along the <211> direction and present multiple twin planes stacked along the <111> direction. An ex situ kinetic study, followed by TEM observations, shows that the 2DHBNs are evolved from triangular nanoprisms through overgrowth along the <211> direction. The gemini surfactant C₁₂C₆C₁₂Br₂ is found to be the most essential factor for the formation of the 2DHBNs. C₁₂C₆C₁₂Br₂ may selectively absorb onto the (111) planes, which promotes the construction of 2D nanostructures. Moreover, C₁₂C₆C₁₂Br₂ can act as an excellent kinetic modifier to control the growth of the nanostructures, which also affects the generation of branched nanostructures. The as-prepared 2DHBNs exhibit an efficient surface-enhanced Raman scattering (SERS) property which has potential application in constructing sensitive SERS substrates.