Abstract
The structural and chemical modification of TiO2 nanotubes (NTs) by the deposition of a well-controlled Au deposit was investigated using a combination of X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), Raman measurements, UV-Vis spectroscopy and photoelectrochemical investigations. The fabrication of the materials focused on two important factors: the deposition of Au nanoparticles (NPs) in UHV (ultra high vacuum) conditions (1–2 × 10−8 mbar) on TiO2 nanotubes (NTs) having a diameter of ∼110 nm, and modifying the electronic interaction between the TiO2 NTs and Au nanoparticles (NPs) with an average diameter of about 5 nm through the synergistic effects of SMSI (Strong Metal Support Interaction) and LSPR (Local Surface Plasmon Resonance). Due to the formation of unique places in the form of “hot spots”, the proposed nanostructures proved to be photoactive in the UV-Vis range, where a characteristic gold plasmonic peak was observed at a wavelength of 580 nm. The photocurrent density of Au deposited TiO2 NTs annealed at 650 °C was found to be much greater (14.7 μA cm−2) than the corresponding value (∼0.2 μA cm−2) for nanotubes in the as-received state. The IPCE (incident photon current efficiency) spectral evidence also indicates an enhancement of the photoconversion of TiO2 NTs due to Au NP deposition without any significant change in the band gap energy of the titanium dioxide (Eg ∼3.0 eV). This suggests that a plasmon-induced resonant energy transfer (PRET) was the dominant effect responsible for the photoactivity of the obtained materials.
Highlights
The decoration of TiO2 nanostructures with noble metal nanoparticles (NPs) such as Au is one way to improve photocatalytic activity,[1] and so such nanostructures are still considered promising materials for solar energy conversion and photocatalytic performance.[2,3] Gold is well known for being chemically inert towards oxidation, which makes photocatalysts modi ed by Au NPs more stable and durable in photocatalytic reactions
Small Au nanoparticles result in higher efficiency.[20]. This mechanism has been described in detail in the work of Naldoni,[1] which demonstrated the in uence of nanoparticle size on the strong metal support interaction (SMSI) effect, which increases the probability of generating charge carriers at the Au/TiO2 interface
The use of Au NPs as a source of the strong absorption of visible light due to the localized surface plasmon resonance (LSPR) and SMSI effects proved to be an effective way to improve the photocatalytic activity of AuNPs/TiO2 NTs samples
Summary
Paper what is known as the strong metal support interaction (SMSI) between metal NPs and metal oxide supports.[8,9,10] Goodman[11,12] explained the SMSI effect for catalytically active Au on titania. Thanks to this the highly ordered structure of nanotubes, the directional movement of photogenerated charges (along the axis of the tubes) to the metallic titanium substrate occurs as as possible, with the result that, photoelectrodes having a wellde ned morphology, structure and good mechanical stability are obtained.[28] TiO2 decorated with gold nanoparticles can ensure efficient charge separation, i.e. recombination of electron–hole pairs, which leads to increased photocatalytic test reactions.[14,22] It is very important, to obtain plasmonic nanoparticles of a speci c size and dispersion on the surface of the photomaterials This makes it possible to apply the thermal evaporation method by using an Au effusion cell under ultra-high vacuum conditions, where the factor controlling the size of nanoparticles is the deposition rate. The mechanism of formation of photo-active centers in such nanomaterials, where the SMSI and LSPR effects play a crucial role, is discussed in this paper as well
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