Effect of carboxylic acids in promoting the radical decomposition of H 2 O 2 in Fenton processes for the treatment of agrochemicals

Abstract

Agrochemicals have become essential to meet the increasing demand for food and other commodities, but they can contaminate the environment, especially water resources, if not properly managed. Advanced Oxidation Processes (AOP), such as Fenton’s process, are a quick alternative to remove these toxic compounds from water and wastewater. Previous studies suggest that carboxylic acids can promote the Fenton reaction by accelerating the degradation rate of H2O2 and the formation of hydroxyl radicals. In this study, formic and acetic acids were applied in a heterogeneous Fenton system to degrade imidacloprid (C9H10N5ClO2), a model agrochemical molecule. Activated limonite and steel wool were used as low-cost heterogeneous iron precursors. The activated limonite was produced by reducing limonite’s iron under H2 flow at 200 and 300°C. The Fenton process with 300°C-activated limonite showed a reaction rate approximately 8-fold higher than the test using natural limonite and 2-fold higher than the one with limonite activated at 200°C. Adding acetic acid to the Fenton process using the 300°C-activated limonite increased the reaction rate by more than 2-fold. When steel wool was used as the iron precursor, the addition of acetic acid resulted in the complete degradation of imidacloprid within one minute of reaction. Acetic acid exhibited a higher promoting activity than formic acid, and the degradation rate increased with increasing concentrations of both carboxylic acids. This study indicates that carboxylic acids can serve as Fenton promoters to increase the degradation rate of agrochemicals, such as imidacloprid, present in water and wastewater.