(Invited, Digital Presentation) Design, Preparation and Characterization of Photofunctional Materials Based on Energy-Resolved Distribution of Electron Traps

Abstract

How can we design functional solid materials, such as catalysts and photocatalysts? What is the decisive structural parameters controlling their activities, performance or properties? What is obtained as structural properties by popular conventional analytical methods, such as X-ray diffraction (XRD) or nitrogen-adsorption measurement, is limited to bulk crystalline structure and specific surface area, i.e., no structural characterization on amorphous phases, if present, and surface structure has been made so far. This is because there have been no macroscopic analytical methods to give surface structural information including possibly-present amorphous phases. Recently, we have developed reversed double-beam photoacoustic spectroscopy (RDB-PAS) which enables measure energy-resolved distribution of electron traps (ERDT) for semiconducting materials such as metal oxides [1,2]. Those detected electron traps (ETs) seem to be predominantly located on the surface for almost all the metal oxide particles, and therefore they reflect macroscopic surface structure, including amorphous phases, in ERDT patterns. Using an ERDT pattern with the data of CB bottom position (CBB), i.e., an ERDT/CBB pattern, it has been shown that metal oxide powders, and the other semiconducting materials such as carbon nitride, can be identified without using the other analytical data such as XRD patterns or specific surface area, and similarity/differentness of a pair of metal-oxide samples can be quantitatively evaluated as degree of coincidence of ERDT/CBB patterns. In this talk, an approach of material design based on the ERDT/CBB-pattern analyses is introduced [3].[1] Nitta, A.; Takase, M.; Takashima, M.; Murakami, N.; Ohtani, B. A Fingerprint of Metal-oxide Powders: Energy-resolved Distribution of Electron Traps. Chem. Commun. 2016, 52, 12096-12099. [2] Nitta, A.; Takashima, M.; Murakami, N.; Takase, M.; Ohtani, B. Reversed double-beam photoacoustic spectroscopy of metal-oxide powders for estimation of their energy-resolved distribution of electron traps and electronic-band structure. Electrochim. Acta 2018, 264, 83-90. [3] Nitta, A.; Takashima, M.; Takase, M.; Ohtani, B. Identification and characterization of titania photocatalyst powders using their energy-resolved distribution of electron traps as a fingerprint. Catal. Today 2019, 321-322, 2-8.