Site-Selective Au⁺ Electroreduction in Titania Nanotubes for Electrochemical and Plasmonic Applications

The present study demonstrates the electrochemical and plasmonic features of gold structures grown in anodic TiO2 nanotubes by means of the electroreduction of Au+ species from a potassium dicyanoaurate electrolyte. The primary location of the electroreduced gold is in the gap between nanotubes, resulting in the formation of a gold/titania interface at the outer shell of the nanotubes. This unique configuration makes it possible to develop a specific shape of gold nanopore array, which is studied as a core–shell structure and standalone gold electrode after the selective dissolution of the titania matrix. Surface plasmon resonance, evaluated by finite-difference time-domain modeling, leads to strong electromagnetic fields and the consequent enhancement in light absorption and light scattering depending on the size, geometry, and composition of the nanostructure. The TiO2 nanotube core promotes light localization in air and water due to its large refractive index. Numerical analysis indicates light E-field enhancement localized on the rims of titania nanotubes of the magnitude intensity of E2 > 100.