Electron spin resonance study of the radicals formed by ultraviolet irradiation of TiO2 in the presence of sulphur dioxide and oxygen

Abstract

A sulphoperoxy radical ([graphic omitted]) has been formed on TiO₂ and studied by electron spin resonance spectroscopy using ¹⁷O-enriched oxygen. It has the following magnetic parameters: g₁= 2.040, g₂= 2.008 and g₃= 2.002; A₁≈A₂≈ 0-G, A₃(O_I)= 106 G and A₃(O_II)= 42 G. This species can be obtained by the reaction at 77 K of SO^–₂ radicals and oxygen. The SO^–₂ is produced on the surface of TiO₂ by heating the sample in the presence of SO₂ at 573 K and quenching at 77 K. A similar SO^–₂ species can be formed by u.v. irradiation of TiO₂ at 77 K in presence of SO₂. A higher concentration of the O₂SOO^– radical is obtained when the irradiation is performed in presence of both oxygen and sulphur dioxide. The O₂SOO^– radical is unstable at 298 K, giving some diamagnetic products via intermediate O^–₂ species (g₁= 2.020, g₂= 2.009 and g₃= 2.002; A₃= 78 G).