New insights regarding the impact of radical transfer and scavenger materials on the OH-initiated phototransformation of phenol

• The degradation rate of PhOH increase significantly in the presence of O2.
• HCOOH and HCOO– have more significant effects than t-BuOH in O2-free solutions.
• t-BuOH, HCOOH and HCOO– have nearly the same effects in the presence of O2.
• The contributions of HO2/O2– to the transformation of PhOH are negligible.
• HO2/O2– contributes mainly to the formation of H2O2.

For the investigations of the oxidative transformations of various organic substances knowledge of the roles and relative contributions of the reactive species formed to the transformations of the target substances is needed. The vacuum ultraviolet (172 nm) photolysis of aqueous solution of phenol (PhOH) (1.0 × 10−4 mol L−1) as model compound was therefore investigated in this work in the presence or absence of various radical scavenger (tert-butanol, t-BuOH) and transfer materials (dissolved O2; formic acid, HCOOH; sodium formate, HCOONa).It was concluded that the rate of degradation of PhOH increased significantly (up to 3-fold) in the presence of dissolved O2 mainly because of the hindered recombination of the primary radicals (H and OH), the increased concentration of OH.All of the applied organic radical scavenger and radical transfer materials decreased the initial rate of degradation of PhOH mainly by reducing the concentrations of reactive primary radicals. In O2-free solutions, the effects of HCOOH and formate anion (HCOO–) were found to be more significant than that of t-BuOH, which can be explained by the different reactivities of the carbon-centred radicals formed. In O2 saturated solutions, there was no significant difference between the initial rates of transformation determined in the presence of the various additives. In these cases, the less reactive HO2 or O2– were the most significant species of the radical set, and it seems that these radicals make only minor contributions to the transformation of PhOH, they contribute mainly to the formation of H2O2 instead.