TiO2 Nanotubes Arrays Loaded with Ligand-Free Au Nanoparticles: Enhancement in Photocatalytic Activity

Materials characterization of TiO2 nanotubes decorated by Au nanoparticles for photoelectrochemical applications

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 (E_g ∼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.

The structural and chemical modification of TiO₂ NTs by the deposition of a well-controlled Au deposit (0.01 mg cm⁻¹) was investigated using a combination of microscopic (SEM, STEM), analytical measurements (XPS, SERS, UV-Vis, XRD) and photoelectrochemical investigations.

Design, synthesis and characterization of doped-titanium oxide nanomaterials with environmental and angiogenic applications

Since the last decade, the metal composite nanostructures have evolved as promising candidates in regard to their wide applications in the fields of science and engineering. Recently, several investigators identified the titanium based nanomaterials as excellent agents for multifunctional environmental and biomedical applications. In this perspective, we have developed a series of zinc-doped (2 and 5%) titanium oxide-based nanomaterials using various reaction conditions and calcination temperatures (TZ1-TZ3: calcined at 500°C, TZ4-TZ6: calcined at 600°C and TZ7-TZ9: calcined at 700°C). The calcined materials (TZ1 to TZ9) were thoroughly analyzed by several physico-chemical characterization methods. The increase of the calcination temperature results in significant changes of the textural properties of the nanostructured materials. In addition, the increase of the calcination temperature leads to the formation of anatase/rutile mixtures with higher quantity of rutile. Furthermore, incorporation of zinc changes the morphology of the obtained nanoparticles. The materials were studied in the photodegradation of methylene blue observing that materials calcined at lower temperatures (TZ1-TZ3) have higher photocatalytic activity than those of the materials calcined at 600°C (TZ4-TZ6), rutile-based systems TZ7-TZ9 are not active. Based on the background literature of titanium and zinc based nanostructures in therapeutic angiogenesis, we have explored the pro-angiogenic properties of these materials using various in vitro and in vivo assays. The zinc-doped titanium dioxide nanostructures (TZ5 and TZ6) exhibited increased cell viability, proliferation, enhanced S-phase cell population, increased pro-angiogenic messengers (ROS: reactive oxygen species and NO: nitric oxide) production and promoted in vivo blood vessel formation in a plausible mechanistic p38/STAT3 dependent signaling cascade. Altogether, the results of the present study showcase these zinc doped-titanium oxide nanoparticles as promising candidates for environmental (water-remediation) and therapeutic angiogenic applications.