Electrolyte-free electro-oxidation of aqueous glyphosate: CuPc-ACF electrode and optimization of operating parameters

A novel approach is proposed in this study for degrading aqueous glyphosate (GLYP) efficiently via electro-oxidation (EO) using a novel copper phthalocyanine (CuPc)-dispersed activated carbon fiber (ACF) electrode. Green synthesis of the CuPc-ACF electrode was achieved by electro-sorption process through oxidation-reduction of the Cu species, using cyclic voltammetry, also for the first time. The prepared electrode was directly applied to degrade the aqueous recalcitrant pollutant without supplementation of an electrolyte and external source of oxidant. Operating parameters of the EO system were optimized via response surface methodology (RSM) based on central composite design using performance index of the area under the curve (AUC). A complete degradation of a synthetic GLYP solution at high concentration (1000 mg L-1) was indicated at the optimized pH and biased potential of 11 and 2.5 V (vs Ag/AgCl), respectively. Kinetic assessment of the experimental data revealed a threshold voltage between 1.5 and 2.0 V required to trigger an effective and irreversible degradation of the aminomethyl phosphonic acid (AMPA) intermediate. The kinetics for degradation of GLYP was proposed via two pathways: a consecutive first-order reversible or an irreversible reaction forming the AMPA intermediate and a parallel reaction forming final transformed products. The study indicated a green route for the synthesis of the CuPc-ACF electrode for complete degradation of GLYP using EO as a green technology. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.