Formation of environmentally persistent free radicals (EPFRs) on ZnO at room temperature: Implications for the fundamental model of EPFR generation

• Published in: Chemical physics letters 2017-02, Vol.670 (C), p.5-10
• Main Authors: Patterson, Matthew C., DiTusa, Mark F., McFerrin, Cheri A., Kurtz, R.L., Hall, Randall W., Poliakoff, E.D., Sprunger, P.T.
• Format: Article
• Language: English
• Subjects: BASIC BIOLOGICAL SCIENCES; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/j.cplett.2016.12.061

[Display omitted] •EPR spectroscopy indicates RT chemisorption of phenol on ZnO forms phenoxy radicals.•FTIR shows the organic is identical to phenoxyl radicals formed after 250°C exposure.•DFT suggests radicals form by oxidizing surface Zn (electron transfer to the organic).•No Zn(III) species exist, suggesting a redox picture of EPFR formation is incomplete. Environmentally persistent free radicals (EPFRs) have significant environmental and public health impacts. In this study, we demonstrate that EPFRs formed on ZnO nanoparticles provide two significant surprises. First, EPR spectroscopy shows that phenoxy radicals form readily on ZnO nanoparticles at room temperature, yielding EPR signals similar to those previously measured after 250°C exposures. Vibrational spectroscopy supports the conclusion that phenoxy-derived species chemisorb to ZnO nanoparticles under both exposure temperatures. Second, DFT calculations indicate that electrons are transferred from ZnO to the adsorbed organic (oxidizing the Zn), the opposite direction proposed by previous descriptions of EPFR formation on metal oxides.