Simultaneous growth of spherical, bipyramidal and wire-like gold nanostructures in solid and solution phases: SERS and electrocatalytic applications

Abstract

Anisotropic growth of gold nanostructures (AuNS) on an indium tin oxide (ITO) substrate and in growth solution was achieved by in situ electrochemical reduction of Au⁺ ions from the growth solution. Initially, the growth solution was prepared by adding the shape-directing agent Cu²⁺ into a solution of cetyltrimethylammonium bromide (CTAB), HAuCl₄ and ascorbic acid (AA). The Au⁺–CTAB complex from the solution was electrochemically reduced to deposit AuNPs on ITO, which act as nucleation centers. The HR-TEM and SEM images exhibit spherical, bipyramidal and wire-like AuNS grown both in solution and on ITO after 1, 3 and 6 h, respectively. The crystallite size and lattice strain were calculated and it was found that the lattice strain decreases with an increase in nucleation time. The ITO/Au-nanowires showed a higher surface coverage (10.1%) and electrochemically active surface area (0.69 cm²) than the other AuNS. Further, the ITO/AuNS exhibited shape-dependent surface enhanced Raman scattering enhancement (SERS) towards 4-aminothiophenol adsorbed on the grown AuNS surface. The ITO/Au-nanowires showed a higher enhancement factor of 9.7 × 10⁵ when compared to the other AuNS. Further, the electrocatalytic activity of the different shaped AuNS was examined towards the reduction of hydrogen peroxide (HP). The Au-nanowire modified ITO electrode exhibited higher electrocatalytic activity towards HP reduction by not only shifting its reduction potential towards less positive potential but also by enhancing its reduction current.