A new view on the mechanism of UV photodegradation of the tricyclic antidepressant carbamazepine in aqueous solutions.

Mechanism of direct UV photolysis of the tricyclic antidepressant carbamazepine (CBZ) at neutral pH was revealed by a combination of nanosecond laser flash photolysis, steady-state photolysis combined with high resolution LC-MS and DFT quantum-chemical calculations. The detection of short-lived intermediates and the detailed identification of final products were performed for the first time. The quantum yield of CBZ photodegradation (282 nm) is about 0.1% and 0.18% in air-equilibrated and argon-saturated solutions. The primary stage is photoionization with the formation of CBZ cation radical followed by a rapid nucleophilic attack by a solvent molecule. The primary photoproducts are 10-oxo-9-hydro-carbamazepine, 9-formylacridine-10(9H)-carboxamide (a result of ring contraction) and various isomers of hydroxylated CBZ. Prolonged irradiation results to accumulation of acridine derivatives, which should lead to an increase of the toxicity of photolyzed CBZ solutions. The obtained results may be important for understanding the fate of tricyclic antidepressants in processes of UVC disinfection and in natural waters under action of sunlight.

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.