Controlled Synthesis of Gold Nanobelts and Nanocombs in Aqueous\nMixed Surfactant Solutions

Abstract

Well-defined gold nanobelts as well as unique gold nanocombs made of nanobelts were readily synthesized by the\nreduction of HAuCl₄ with ascorbic acid in aqueous mixed solutions of the cationic surfactant cetyltrimethylammonium\nbromide (CTAB) and the anionic surfactant sodium dodecylsulfonate (SDSn). Single-crystalline gold nanobelts grown\nalong the <110> and <211> directions were prepared in mixed CTAB−SDSn solutions at 4 and 27 °C, respectively.\nFurthermore, single-crystalline gold nanocombs consisting of a <110>-oriented stem nanobelt and numerous <211>-oriented nanobelts grown perpendicularly on one side of the stem were fabricated by a two-step process with temperature\nchanging from 4 to 27 °C. It was proposed that the mixed cationic−anionic surfactants exerted a subtle control on\nthe growth of gold nanocrystals in solution due to the cooperative effect of mixed surfactants. This synthetic strategy\nmay open a new route for the mild fabrication and hierarchical assembly of metal nanobelts in solution. The obtained\ngold nanobelts showed good electrocatalytic activity toward the oxidation of methanol in alkaline solution; in particular,\nthe electrode modified with the nanobelts obtained at 27 °C exhibited an electrocatalytic activity considerably higher\nthan normal polycrystalline gold electrode. Moreover, the gold nanobelts were used as the surface-enhanced Raman\nscattering (SERS) substrate for detecting the enhanced Raman spectra of <i>p</i>-aminothiophenol (PATP) molecules, and\nthe gold nanobelts obtained at 4 °C exhibited an unusual larger enhancement of the b₂ modes relative to the a₁ modes\nfor the adsorbed PATP molecules.