Seminars Archive

The role of TiO2 defects in plasmonics/semiconductors interaction

Abstract
Solar to energy (electricity or to fuels) conversion based on semiconductors is a prominent target for a renewable energy economy. Recently, it has been posited that charge carriers (hot electrons), either directly transferred from a plasmonic structure to a neighbouring semiconductor (such as TiO2), or induced by energy transfer (plasmonic resonant energy transfer, PRET), could augment photoconversion processes, enabling the design of plasmonic devices that can harvest photons over the entire solar spectrum and beyond. [1,2] So far, mechanistic study of plasmonics/semiconductors interaction has been limited to inorganic system for the water splitting reaction pointing out that both hot electron transfer and PRET can be responsible for activity enhancements, with the PRET being active only in the presence of energy match between the SP resonance of metals (e.g., Au, Ag) and the bandgap of the semiconductors (e.g., N-doped TiO2, α-Fe2O3). [3] The presentation will focus on the interaction mechanism between SPR absorption of Au NPs and various defective TiO2 in the plasmonic photo- oxidation of formic acid. Through the selective excitation of the Au SPR band we study its electronic interaction with electronic intra-bandgap states of different Au/TiO2 composites with stoichiometric, N-doped, and black TiO2 [4] with different nominal Au loading (1, 3, 5, 7.5, 10 %) Photocatalytic efficiency is strictly related to electronic structure of TiO2. Specifically, while at low Au loading (up to 5%) hot electrons transfer plays a major role in determining the catalyst activity, at high Au loading (10 %) there are evidence for TiO2 defects-dependent PRET occurrence. References [1] Mubeen et al. Nat. Nanotech. 2013, 8, 247. [2] Polman et al. Nat. Mater. 2009, 9, 205. [3] Thimsen et al. Energy & Environ. Sci. 2012, 5, 5133. [4] Naldoni et al. JACS 2012, 134, 7600.