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Titanium and Zinc Oxide Nanoparticles Are Proton-Coupled Electron Transfer Agents

Science  08 Jun 2012:
Vol. 336, Issue 6086, pp. 1298-1301
DOI: 10.1126/science.1220234

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Pluses and Minuses

Because of their high surface area and tunable electronic structure, nanoparticles are of interest for next-generation photocatalysis and light-harvesting applications. Many of these applications involve electron transfer events at the particle surface after light absorption. Schrauben et al. (p. 1298) now show, through a series of radical trap kinetic studies, that proton transfer can concurrently accompany electron transfer at the solvent interfaces of two common nanoparticle formulations (oxides of titanium and of zinc). The results may help in the optimization of particle structure and energetics.

Abstract

Oxidation/reduction reactions at metal oxide surfaces are important to emerging solar energy conversion processes, photocatalysis, and geochemical transformations. Here we show that the usual description of these reactions as electron transfers is incomplete. Reduced TiO2 and ZnO nanoparticles in solution can transfer an electron and a proton to phenoxyl and nitroxyl radicals, indicating that e and H+ are coupled in this interfacial reaction. These proton-coupled electron transfer (PCET) reactions are rapid and quantitative. The identification of metal oxide surfaces as PCET reagents has implications for the understanding and development of chemical energy technologies, which will rely on e/H+ coupling.

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