3.2.3. pH dependence of the photolysis of H2O2 and O2H The pH dependence of the photolysis of H2O2 has been reported, the rate of photolysis increasing in more alkaline conditions (Legrini et al., 1993). H2O2 is slightly acidic and with a dissociation constant (Ka) of 1.78 1012 at 20 C (Ardon,1964), its dissociation to Hþ and O2H is increased when pH > pKa (i.e., 11.75). In addition, the generation of OH by the dismutation reaction between O2H and H2O2 is maximal when pH ¼ pKa (Legrini et al., 1993).
The relationship between pH and pKa can be expressed as (Ardon, 1964):