Figure 2. Hydroxyl radical (HO^•) generation from TiO₂ in the presence of H₂O₂. (A) The time course of ESR spectrum from TiO₂ measured by EPR spin-trapping following the addition of H₂O₂ at time 0 and with DMPO as a spin trap. (B) Monitoring of the spin concentration of the HO^• generated from TiO₂ in the presence of H₂O₂. All data are presented as the mean (n = 3–5). Experimental conditions are described in "MATERIALS & METHODS" and illustrated in Fig. 1.