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We have examined the formation of environmentally persistent free radicals (EPFRs) from phenol over alumina and titania using both powder and single-crystal samples. Electron paramagnetic resonance (EPR) studies of phenol adsorbed on metal oxide powders indicates radical formation on both titania and alumina, with both oxides forming one faster-decaying species (lifetime on the order of 50-100 h) and one slower-decaying species (lifetimes on the order of 1000 h or more). Electron energy loss spec- troscopy (EELS) measurements comparing physisorbed phenol on single-crystal TiO2(1 1 0) to phenoxyl radicals on the same substrate indicate distinct changes in the π-π* transitions from phenol after radical formation. The identical shifts are observed from EELS studies of phenoxyl radicals on ultrathin alumina grown on NiAl(11 0), indicating that this shift in the π-π* transition may be taken as a general hallmark of phenoxyl radical formation. © 2012 Elsevier B.V. All rights reserved.

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Chemical Physics

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