Electron- and hole-mediated reactions in UV -irradiated O2 adsorbed on reduced rutile TiO2(110)
The photon-stimulated reactions in oxygen adsorbed on reduced TiO2(110) at low temperatures (< 100 K) are studied. The amount of O2 desorbed by UV irradiation is found to be a non-linear function of the amount of O2 chemisorbed on the surface, theta O2. For theta O2 > 1 O2 per bridging oxygen vacancy, the O2 photodesorption yield is ~4 times greater than the yield for theta O2 < 1 O2 per vacancy. We also find that for a fixed amount of chemisorbed 18O2, its PSD yield increases substantially if 16O2 is subsequently chemisorbed. The results indicate that the hole-mediated O2 photodesorption probability depends on the charge state of the chemisorbed O2 .-. it decreases for more negatively charged O2. Since the charge state of the chemisorbed O2 depends on the total oxygen coverage, the coverage influences the photodesorption process. For a saturation coverage of chemisorbed oxygen, only ~40% of the oxygen desorbs after prolonged UV irradiation. However, when weakly bound (physisorbed) oxygen is also present, ~70% of the initially chemisorbed O2 photodesorbs. Of the O2 remaining on the surface after UV irradiation, some is dissociated, while the rest is left in a non-dissociated state that is inactive for hole-mediated photodesorption. We propose that reactions between the chemisorbed O2 and electrons (promoted to the conduction band by the UV irradiation) explain the low total photodesorption yield when no physisorbed O2 is present. A simple model based on the oxygen coverage and the charge of the chemisorbed oxygen, which accounts for the observations, is presented.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1002162
- Report Number(s):
- PNNL-SA-71556; 24799; 24800; KC0301020; KC0302010; TRN: US201102%%614
- Journal Information:
- Journal of Physical Chemistry C, 115(1):152-164, Vol. 115, Issue 1; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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