Oxidative degradation of chlorpyrifos using ferrate(VI): Kinetics and reaction mechanism

Abstract

In this study, we investigated the degradation kinetics of chlorpyrifos, an organophosphorus (OP) compound, using ferrate(VI), and investigated the potential of this iron-based chemical oxidant on chlorpyrifos removal from water and wastewater treatments. A series of kinetic experiments were conducted to evaluate the influence of various environmental factors, such as pH, oxidant dosages, as well as the presence of anions, cations, humic acid (HA), and different water matrices. Chlorpyrifos was completely removed within 300 s under the following optimum conditions: [chlorpyrifos]₀ = 1 μM, [Fe(VI)]₀:[chlorpyrifos]₀ = 100:1, T = 25 °C, and pH = 7.0. Anions such as Cl^-, SO₄^2-, NO₃^-, and HCO₃^- and cations such as Fe³⁺, Cu²⁺, and NH₄⁺ did not appear to influence the removal of chlorpyrifos. However, the presence of Ca²⁺, Mg²⁺, and HA in water inhibited the degradation of chlorpyrifos. Experiments on removing chlorpyrifos from tap water, river water, and synthetic wastewater were performed to demonstrate the practical applications of Fe(VI). Ten oxidation products of chlorpyrifos were identified using liquid chromatography-quadrupole-time-of flight-mass spectrometry (LC-Q-TOF-MS), and their structures were further elucidated using MS/MS spectra. Then, two degradation pathways were preliminarily proposed including the oxidation of the P = S bond, cleavage of C-O bond, and hydroxyl substitution reaction. In general, Fe(VI) could be used as an efficient technology for chlorpyrifos removal from water and wastewater treatments.

Keywords: Chlorpyrifos; Ferrate(VI); Mechanism; Products; Theoretical calculation.