In this study, TiO₂ nanowires on TiO₂ nanotubes arrays (TNWs/TNAs) and Au-decorated TNWs/TNAs nanostructures are designed and fabricated as a new type of photoanode for photoelectrochemical (PEC) water splitting. The TNWs/TNAs were fabricated on Ti folds by anodization using an aqueous NH₄F/ethylene glycol solution, while Au nanoparticles (NPs) and Au nanorods (NRs) were synthesized by Turkevich methods. We studied the crystal structure, morphology, and PEC activity of four types of nanomaterial photoanodes, including TNWs/TNAs, Au NPs- TNWs/TNAs, Au NRs-TNWs/TNAs, and Au NPs-NRs-TNWs/TNAs. The TiO₂ and Au-TiO₂ samples exhibited pure anatase phase of TiO₂ with (0 0 4), (1 0 1), and (1 0 5) preferred orientations, while Au-TiO₂ presented a tiny XRD peak of Au (111) due to a small Au decorated content of 0.7 ± 0.2 at.%. In addition, the samples obtained a well-defined and uniformed structure of TNAs/TNWs; Au NPs (size of 19.0 ± 1.9 nm) and Au NRs (width of 14.8 ± 1.3 nm and length of 99.8 ± 15.1 nm) were primarily deposited on TNWs top layer; sharp Au/TiO₂ interfaces were observed from HRTEM images. The photocurrent density (J) of the photoanode nanomaterials was in the range of 0.24–0.4 mA/cm². Specifically, Au NPs-NRs- decorated TNWs/TNAs attained the highest J value of 0.4 mA/cm² because the decoration of Au NPs and Au NRs mixture onto TNWs/TNAs improved the light harvesting capability and the light absorption in the visible-infrared region, enhanced photogenerated carriers’ density, and increased electrons’ injection efficiency via the localized surface plasmon resonance (LSPR) effect occurring at the Au nanostructures. Furthermore, amongst the investigated nanophotocatalysts, the Au NPs-NRs TNWs/TNAs exhibited the highest photocatalytic activity in the degradation of methylene blue with a high reaction rate constant of 0.7 ± 0.07 h⁻¹, which was 2.5 times higher than that of the pristine TNWs/TNAs.

A UPLC-MS/MS method was developed for detecting five pesticide residues; advanced TiO ₂ nanostructured films showed high pesticide photodegradation and antimicrobial activity.