Electrodegradation of 2,4-dichlorophenoxyacetic acid herbicide from aqueous solution using three-dimensional electrode reactor with G/β-PbO2anode: Taguchi optimization and degradation mechanism determination

Abdollah Dargahi,Ghorban Asgari,Amin Ansari,Davood Nematollahi,Reza Shokoohi,Mohammad Reza Samarghandi

doi:10.1039/c8ra08471h

Abstract

This study aimed to investigate the electro-degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) from aqueous solution using two and three-dimensional electrode (2D and 3D) reactors with graphite(G)/β-PbO2 anode. To increase the degradation efficiency, affecting parameters on the electro-degradation process were investigated and optimized by adopting the Taguchi design of experiments approach. The structure, morphology and electrochemical properties of the electrodes were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), linear sweep voltammetry and cyclic voltammograms. The controllable factors, i.e., electrolysis time, 2,4-D initial concentration, solution pH and current density (j) were optimized. Under optimum conditions, the 2,4-D degradation efficiency was 75.6% using 2D and 93.5% using 3D electrode processes. The percentage contribution of each controllable factor was also determined. The pH of the solution was identified as the most influential factor, and its percentage contribution value was up to 39.9% and 40.4% for 2D and 3D electrode processes, respectively. Considering the parameters of the kinetics, it was found that the degradation of 2,4-D and removal of COD using the G/β-PbO2 electrode obey the pseudo-first order kinetics. In addition, the mineralization pathway of 2,4-D at G/β-PbO2 electrode was proposed. The results also demonstrated that the 3D electrode process with G/β-PbO2 anode can be considered as a useful method for degradation and mineralization of 2,4-D herbicides from aqueous solution.

Highlights

In recent years, the contamination of surface and groundwater by pesticides has become a serious environmental problem due to the extensive use of these chemicals in farmland, gardens and forest lands
The scanning electron microscopy (SEM) technique was used to assess the microstructure of studied electrode under different magni cations and the obtained results were shown in Fig. S3(a).† These gure illustrated the agglomeration of the particles with limited individual particle boundary
Energy-dispersive X-rays (EDX) technique was utilized to determine the elemental structure of the b-PbO2 and its results were represented in Fig. S3(b).† These gure shows that the main elements existed in the b-PbO2 were the oxygen (O) and lead (Pb)

Summary

Introduction

The contamination of surface and groundwater by pesticides has become a serious environmental problem due to the extensive use of these chemicals in farmland, gardens and forest lands. Considering their extensive application, the human exposure to such pesticides is almost predictable, which may lead to detrimental effects on human health, including carcinogenicity and mutagenicity.. The term pesticide is a generic name, which includes a number of the biologically-active compounds, e.g., herbicides, fungicides and insecticides. 2,4-Dichlorophenoxyacetic acid, 2,4-D, is known as one of the oldest and most widely used herbicides in the world, its application dating back to 1945, and it is applied for the selective control of weeds in gardens and farms.

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