Fe (III) carboxylate complexes are photoactive natural compounds that are intensively studied and are considered to be one of the promising systems for the degradation of pollutants in the so-called advanced oxidation processes (AOPs). They demonstrate high quantum yields of photolysis and efficient generation of ^•OH radicals under the action of UV radiation. However, there is very little information on the quantum yields of ^•OH radicals (_/_OH) upon excitation of such systems and relation of _/_OH values with quantum yield of photolysis of Fe(III) carboxylates (_/_phot). At the same time, the _/_OH values and the reactivity of ^•OH with respect to the target compounds are the most important parameters for the application of any photosystem in AOPs. This work presents valid approach to determining both _/_OH and _/_phot values during UV photolysis of natural Fe(III) carboxylate complexes and to establishing correlation between these parameters.

The approach [1,2] is based on the use of the FeOH²⁺ hydroxocomplex as a reference system with the well-known _/_OH value and benzene as a selective trap for ^•OH radicals. For the first time [1], _/_OH was determined for the most popular Fe(III)-oxalate photosystem in a wide range of initial parameters (pH, excitation wavelength, concentration of oxalate and Fe(III) ions). Also, the oxidative potential of the oxalate photosystem was tested on a set of resistant organic herbicides, and the quantum yields of photodegradation of these herbicides were compared with the _/_OH value [1]. It was shown that dark processes of Fe(II) reoxidation by dissolved oxygen play an important role in correct determination of both _/_OH and _/_phot values and correct procedure of calculation of this parameters from experimental data was proposed [2]. Good linear correlation between _/_OH and _/_phot was established for a set of natural Fe(III) carboxylates.

This work was financially supported by the Russian Science Foundation (No. 21-43-00004).

[1] Yu.E. Tyutereva, M.V. Novikov, O.A. Snytnikova and I.P. Pozdnyakov, How to measure quantum yield of hydroxyl radical during photolysis of natural Fe(III) carboxylates? Chemosphere, 298 (2022) 134237 DOI: 10.1016/j.chemosphere.2022.134237

[2] Yury A. Belikov, Olga A. Snytnikova, Vyacheslav P. Grivin, Victor F. Plyusnin, Jing Xu, Feng Wu and Ivan P. Pozdnyakov, Photolysis of Fe(III) complex with ethylenediamine-N,N'-disuccinic acid and its efficiency in generation of •OH radical, Chemosphere, 309 (2022) 136657, DOI: 10.1016/j.chemosphere.2022.136657