Controlled attachment of gold nanoparticles on ordered titania nanotube arrays

Gold nanoparticles on titanium oxide support are known to have excellent properties suitable for photocatalytic applications such as water splitting, CO oxidation, etc. Recent advances in titania nanotube arrays synthesized by electrochemical anodization processes provide ideal supports for such applications. We report here for the first time the successful attachment of gold nanoparticles onto electrochemically-anodized titania nanotube arrays. A deposition-precipitation method has been used which is applicable for both low- and high-aspect ratio nanotubes, with lengths of the order of 0.5 mm and 5 mm respectively. Uniform coverage of gold nanoparticles both inside and outside the nanotubes has been achieved. Very good control over the gold nanoparticle diameters (in the range of 1-10 nm) and coverage percentage (up to 70%) has been demonstrated by adjusting the soaking time. With respect to immediate applications two specific results are promising: i) deposition of gold nanoparticles with diameters <5 nm, ideal for photocatalytic applications, has been achieved; ii) coalescence of nanoparticles to almost total coverage of the nanotube surfaces with a thin layer (similar to 10 nm) of metallic gold after very long exposure to the gold solution suggests the possibility of formation of localized Schottky barriers for current control.