Electron Source in Photoinduced Hydrogen Production on Pt-supported TiO Particles
Abe et al. illuminated an aqueous suspension of TiO/Pt with a Hg arc lamp and observed H production in the absence of O production. An unspecified elemental analysis excluded carbonaceous contaminants, and the source of the electron donor was concluded to be Ti+ cations. We can suggest at least three more likely (than Ti) sources for their mysterious electron donor: (1)an overlooked inorganic species, (2) Ti, and/or (3)organic impurities. The authors excluded the latter in their paper, but we view this conclusion as suspect given the lack of information on the limits of detection of the carbon assay, and the fact that the choice of argon(thermal conductivity= 41.33 x 10-6 cal cm-2s-1 (C cm-1)-1)3 as a carrier gas in their thermal conductivity detector4 probably precluded the observation of CO (thermal conductivity= 37.61 x 10-6 cal cm-2s-1 (C cm-1)-1)3, which is a common product of organic photochemical oxidations. No mention is made of an analysis for inorganic impurities. It is widely accepted that nanometer scale TiO particles can have significant fractions of undercoordinated Ti sites which can be easily oxidized to Ti, the highest valence of Ti observed in condensed phases. Here we point out that oxidation of Ti to Ti is much more physically realistic than oxidation of Ti to Ti. Removal of a fifth electron from titanium requires {approx}56 eV5.Ti, if it were to be generated in a solid oxide, would extract an electron from the valence band composed mainly of oxygen 2s and 2p states rather than remain in the 5 valence state. This unrealistically high oxidation state seems even more unlikely given the fact that at the room temperatures used in the authors' reactions Ti would have been generated and remained at the surface (at room temperature the diffusion of Ti cations in TiO is minimal), and the fact that the surface Madelung potential is smaller than that of the bulk6.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 15007651
- Report Number(s):
- PNNL-SA-33161; TRN: US200419%%399
- Journal Information:
- Journal of Physical Chemistry B, Vol. 105, Issue 2; Other Information: PBD: 18 Jan 2001
- Country of Publication:
- United States
- Language:
- English
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