X-ray Photoelectron Spectroscopy (XPS) Analysis of Ultrafine Au Nanoparticles Supported over Reactively Sputtered TiO2 Films

Abstract

The impact of a titania (TiO2) support film surface on the catalytic activity of gold nanoparticles (Au NP) was investigated. Using the reactive dc-magnetron sputtering technique, TiO2 films with an amorphous, anatase, and nitrogen-doped anatase crystal structure were produced for a subsequent role as a support material for Au NP. Raman spectra of these TiO2 films revealed that both vacuum and NH3 annealing treatments promoted amorphous to anatase phase transformation through the presence of a peak in the 513–519 cm−1 spectral regime. Furthermore, annealing under NH3 flux had an associated blue shift and broadening of the Raman active mode at 1430 cm−1, characteristic of an increase in the oxygen vacancies (VO). For a 3 to 15 s sputter deposition time, the Au NP over TiO2 support films were in the 6.7–17.1 nm size range. From X-ray photoelectron spectroscope (XPS) analysis, the absence of any shift in the Au 4f core level peak implied that there was no change in the electronic properties of Au NP. On the other hand, spontaneous hydroxyl (–OH) group adsorption to anatase TiO2 support was instantly detected, the magnitude of which was found to be enhanced upon increasing the Au NP loading. Nitrogen-doped anatase TiO2 supporting Au NP with ~21.8 nm exhibited a greater extent of molecular oxygen adsorption. The adsorption of both –OH and O2 species is believed to take place at the perimeter sites of the Au NP interfacing with the TiO2 film. XPS analyses and discussions about the tentative roles of O2 and –OH adsorbent species toward Au/TiO2 systems corroborate very well with interpretations of density functional theory simulations.

Green Synthesis of TiO2 Using Impatiens rothii Hook.f. Leaf Extract for Efficient Removal of Methylene Blue Dye

“…The area ratio of Ti 4+ 2p 1/2 to Ti 4+ 2p 3/2 was 0.65 approximately. The difference in binding energy due to the spin orbit coupling, Δ E b = E b (464.14 eV) – E b (458.66 eV) was 5.7 eV, which is well-matched with the reported values. , The O 1s spectra of IL–TiO 2 showed two peaks at binding energies of 530.5 eV and a minor peak at 532.014 eV (Figure B), which are attributed to oxygen anions (O–Ti–O) and surface hydroxyl (−OH) species, respectively …”

Assessing and Quantifying Thermodynamically Concomitant Degradation during Oxygen Evolution from Water on SrTiO3

“…The core-level shift can be ascribed to a change in the chemical environment surrounding Ti atoms. A similar shift of the Ti 2p XPS was previously seen in annealed TiO 2 samples and assigned to a locally distorted O h symmetry with a higher oxidation state of the Ti . A corresponding one in the e g peaks of Ti L-edge XAS on SrTiO 3 has likewise been associated with octahedral distortions related to defects .…”

“…A similar shift of the Ti 2p XPS was previously seen in annealed TiO 2 samples and assigned to a locally distorted O h symmetry with a higher oxidation state of the Ti. 39 A corresponding one in the e g peaks of Ti L-edge XAS on SrTiO 3 has likewise been associated with octahedral distortions related to defects. 40 Therefore, the Ti XAS and XPS data together identify local TiO 2 that maintains the octahedral cage of the perovskite, albeit a distorted one.…”

Formation of a Nanorod-Assembled TiO2 Actinomorphic-Flower-like Microsphere Film via Ta Doping Using a Facile Solution Immersion Method for Humidity Sensing

“…The narrow scan of O 1s contained an O–Ti peak at around 529.57 eV and 530.37 eV for UTD and TAFM-3 ( Figure 4 f). Another lower-intensity peak appeared at 531.2 eV and was ascribed to the presence of the hydroxyl group (OH) [ 46 , 47 ]. This OH group was generated from dissociated water adsorption on oxygen vacancies [ 45 ].…”