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(OI)= 106 G and A3(OII)= 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).