Study of some electron transfer reactions of titanium dioxide

Abstract

Pigmentary samples of titanium dioxide react with electron acceptors such as quinones, tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane to give paramagnetic species. In some cases these could be identified from their e.p.r. spectra as being the radical anion of the acceptor. Visible absorption spectra measurements confirmed these assignments. Electron transfer to bipyridinium salts also occurs, with the formation of their respective radical cations. Anthracene and perylene react with activated samples of the oxide to give paramagnetic species which are probably the hydrocarbon radical cations. The electron transfer reactions are discussed in terms of factors which affect electron donation from the oxide, ease of reduction of acceptors and ease of oxidation of donors and the adsorption of organic compounds on the surface of the oxide.