Degradation of herbicide 2,4-dichlorophenoxybutanoic acid in the photolysis of [FeOH]2+ and [Fe(Ox)3]3− complexes: A mechanistic study

• 2,4-DB undergoes extensive degradation during the photolysis of [FeOH]2+ and [Fe(Ox)3]3− complexes.
• ROS species (mainly OH radical) are responsible for the photodecomposition of herbicide.
• Detailed scheme of 2,4-DB photodegradation including 30 photoproducts was proposed.
• Both complexes can greatly accelerate the photodegradation of 2,4-DB in natural water systems.

In the present work the Fe(III)-assisted photodegradation of the herbicide 2,4-dichlorophenoxybutanoic acid (2,4-DB) has been studied by means of stationary (308 nm) and laser flash (355 nm) photolysis. The initial quantum yield of 2,4-DB photodegradation in [FeOH]2+ and [Fe(Ox)3]3− systems was evaluated to be 0.11 and 0.17 upon 308 nm exposure, respectively. The prolonged photolysis of [FeOH]2+ and [Fe(Ox)3]3− systems results in the complete degradation of 2,4-DB with almost complete mineralization of herbicide and its aromatic products in the case of [FeOH]2+ photolysis and the accumulation of some persistent aromatic products in the case of [Fe(Ox)3]3− photolysis. For both systems the main primary products of 2,4-DB photolysis determined by liquid chromatography – mass spectrometry are products of the hydroxylation, the substitution of chlorine atom to OH group, the loss of aliphatic tail and the opening of benzene ring. The obtained results indicate ROS species (mainly OH radical) to be responsible for the herbicide photodegradation.

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