In acidic and neutral conditions, the dissociation of H2O2 toO2H was negligible. As the initial pH increased from 7 to 10,the H2O2 concentration decreased from 10 mMto 9.83 mM and the Fl,i absorbed by H2O2 reduced from 28.9% to 26.9%. Despite only 1.7% of H2O2 being dissociated to O2H at pH 10, the Fl,i of O2H increased from 0% to 5.9%. In total, 32.8% of the incident spectral radiant power was absorbed by H2O2 and O2H at pH 10 and this corresponded to a net increment of 3.9% compared with that absorbed by H2O2 alone at pH 7. This increase in the
combined Fl,i absorbed by H2O2 and O2H can be explained by the significantly higher 3254 of O2H, which is about 12 times higher than that of H2O2. Since both H2O2 and O2H absorb UVC irradiation to produce OH (Legrini et al., 1993), this
implies that more OH can be produced when H2O2 dissociates to O2H at higher pH such as pH 10.