Photolysis of aqueous H₂O₂: Quantum yield and applications for polychromatic UV actinometry in photoreactors

Methanol is used to measure the yield of ^•OH radicals produced in the photolysis of H₂O₂ in aqueous solutions. The UV photolysis of H₂O₂ generates ^•OH radicals, which in the presence of methanol, oxygen, and phosphate buffer form formaldehyde, namely, Φ(HCHO) = Φ(^•OH). The quantum yield of ^•OH has been redetermined in view of literature inconsistencies resulting in Φ(^•OH) = 1.11 ± 0.07 in the excitation range of 205-280 nm. The constancy of Φ(^•OH) and the ease and sensitivity of the formaldehyde product analysis makes the H₂O₂/CH₃OH system suitable for polychromatic UV actinometry. In addition, the relatively low cost of the main components and the possibility of destroying the methanol before disposal qualify the system for both monochromatic and polychromatic actinometry in a large volume of water. The H₂O₂/CH₃OH system was applied in different commercial UV photoreactors.