Semitransparent Gold-Embedded Anodic Titania Nanotubes: Harnessing Plasmonic and Photoelectrochemical Synergies for Visible-Light Applications

Anodic titania nanotubes are characterized by their high degree of vertical alignment, resulting in structures with exceptional surface area, physical, and electrochemical properties. However, their intrinsic wide band gap (ca. 3.2 eV for anatase form) limits their absorption to the UV spectrum, necessitating strategies such as doping and plasmonic decoration to extend their activity into the visible range. Additionally, the semitransparency of these structures can be leveraged to enhance light management and integration into optoelectronic and solar-energy-harvesting devices.

Gold nanoparticles decorated anodic titania nanotubes, exhibiting localized surface plasmon resonance, can potentially improve photocatalytic activity, visible-light absorption, nonlinear optical behavior, and the efficiency of solar energy and photonic devices. These materials can be synthesized through various approaches, including laser-treated titania nanotubes coated with a gold thin film or the laser treatment of oxide nanotubes formed from TiAu homogeneously co-sputtered alloys. However, laser processing often results in non-uniform gold nanoparticle distribution, predominantly on the nanotube surface area, leading to issues like melting, agglomeration, or polydispersity. To address these challenges, we have developed semitransparent anodic nanotubes embedded with gold nanoparticles. These structures were fabricated by anodizing a multilayered film stack composed of alternating Ti-sputtered layers and TiAu co-sputtered layers. SEM analysis revealed well-formed, uniformly distributed nanotubes and the Raman spectra confirmed the presence of the anatase phase in the prepared materials, with up to 7 % of Au content. The UV–vis spectra also revealed a redshift of the absorption band beyond 400 nm, and energy band-gap reduction was observed compared to the bare titania material. Furthermore, the samples exhibited superior anodic current densities, particularly favoring oxygen evolution reactions, reaching up to 2.7 mAcm^-2 for the sample with 5 % Au content. These results underscore the potential of such gold nanoparticle-embedded nanotubular architectures for advanced photoelectrochemical applications.