(496h) Insights into the Basic Mechanisms at Solvent/TiO2/Au Interfaces Associated to Hydrogen Production By Photoreduction of Water

The use of semiconductors for hydrogen production through water splitting represents a clean and long lasting renewable source of energy, since it is produced from natural sources such as sunlight and water. Among semiconductors, titanium dioxide (TiO₂) remains a benchmark photocatalyst with high stability, low cost, low toxicity and it is well known that its structural properties are strongly correlated to the deposition method and post-treatment process, such as annealing. However, in order to design a suitable light harvesting material, it is necessary to understand the mechanisms that take place at the water-semiconductor interface. Ideally, the semiconductor surface provides the positive and negative sites where the redox reactions take place. Nevertheless, is it well known that TiO₂ anatase has an inherent defective surface where oxygen vacancies and titanium interstitial sites play an important role in the water splitting reaction. This work focuses on the study of the correlation of the defective TiO₂ surface with the charge transport mechanisms in bare thin films deposited by physical vapor deposition (PVD) and in TiO₂/Au nanoparticles (NPs) nanostructures. The films were characterized by Scanning (SEM) and Transmission Electron Microscopy (TEM), X-ray diffraction (XRD) and UV-Vis spectroscopy. X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) revealed that oxygen vacancies can be created upon annealing and are associated with distortions in the geometric structure of the anatase phase. Furthermore, PL measurements in different media (water, ethanol, vacuum and air) elucidate the correlation of the vacancies with the creation of shallow and deep states in the band gap. This analysis is supported by DDA and DFT simulations. Furthermore, these findings explain the synergetic mechanisms on the Au/TiO₂ structures where the contribution of the plasmonic NPs is coupled with the defective surface of the semiconductor to increase the photocatalytic activity.

References:

1. Cure, J.; Assi, H.; Cocq, K.; Marin, L.; Fajerwerg, K.; Fau, P.; Beche, E.; Chabal, Y. J.; Esteve, A.; Rossi, C., Controlled Growth and Grafting of High-Density Au Nanoparticles on Zinc Oxide Thin Films by Photo-Deposition. Langmuir 2018, 34 (5), 1932-1940.
2. Mendoza-Diaz, M.-I.; Cure, J.; Rouhani, M. D.; Tan, K.; Patnaik, S.-G.; Pech, D.; Quevedo-Lopez, M.; Hungria, T.; Rossi, C.; Estève, A., On the UV–Visible Light Synergetic Mechanisms in Au/TiO2 Hybrid Model Nanostructures Achieving Photoreduction of Water. The Journal of Physical Chemistry C 2020, 124 (46), 25421-25430.
3. Cure, J.; Cocq, K.; Nicollet, A.; Tan, K.; Hungria, T.; Assie-Souleille, S.; Vivies, S.; Salvagnac, L.; Quevedo-Lopez, M.; Maraval, V.; Chauvin, R.; Esteve, A.; Rossi, C., A Beehive Inspired Hydrogen Photocatalytic Device Integrating a Carbo-Benzene Triptych Material for Efficient Solar Photo-Reduction of Seawater. Adv Sustain Syst 2020.