Identification of oxygen species adsorbed on reduced titanium dioxide

Abstract

The nature of oxygen adsorbed on slightly reduced TiO₂ has been investigated using oxygen enriched with ¹⁷O₂. On anatase, the oxygen adsorbs as O^–₂ with a hyperfine splitting A_xx about g₃ of 77 G; no structure could be resolved for A_yy and A_zz. On rutile, oxygen adsorbs as O^–₂ on two sites of different thermal stability; (I) with g₁= 2.030, g₂= 2.008, g₃= 2.004 and A_xx= 76 G, and (II) with g₁= 2.020, g₂= 2.009, g₃= 2.003 and A_xx= 72 G. The evidence indicates that O^–₂ exists in a largely ionic form on TiO₂ and other oxides. A symmetrical line at g= 2.003 which appears on some anatase samples after oxygen adsorption is attributed to the localization of a conduction electron by the adsorbed oxygen.