How to measure quantum yield of hydroxyl radical during photolysis of natural Fe(III) carboxylates?

The efficiency of oxidative species generation is one of the crucial parameters for the application of any system based on advanced oxidation processes (AOPs). This paper presents an approach to the correct determination of quantum yields of the hydroxyl radical upon UV photolysis of natural Fe(III) carboxylates, which are widely used in the works devoted to Environmental Chemistry and Water Treatment. The approach is based on the use of [FeOH]2+ hydroxocomplex as a reference system with the well-known quantum yield of hydroxyl radical and benzene as a selective trap for the •OH radical. For the first time, the quantum yields of the •OH radical have been determined for the most popular Fe(III) oxalate photosystem in the wide range of initial parameters (pH, excitation wavelength, concentration of oxalate and Fe(III) ions). Also the oxidation potential of Fe(III) oxalate photosystem was tested on a set of persistent organic herbicides, and quantum yields of the photodegradation of herbicides were compared with the quantum yield of the •OH radical. The Fe(III) oxalate photosystem is recommended as a suitable system for the generation of •OH radical at neutral pH under UV radiation.