ESR signal of superoxide radical anion adsorbed on TiO2 generated at room temperature

The electron spin resonance spectrum of superoxide anion radical adsorbed on the surface of colloidal TiO2 was detected directly at room temperature for the first time. This signal was generated partially by porphyrin-sensitized titanium dioxide, i.e., the reduction of adsorbed oxygen on the TiO2 nanocluster surface by the just injected electron from the excited porphyrin.