Efficient degradation of chloroquine drug by electro-Fenton oxidation: Effects of operating conditions and degradation mechanism

Abstract

In this work, the degradation of chloroquine (CLQ), an antiviral and antimalarial drug, using electro-Fenton oxidation was investigated. Due to the importance of hydrogen peroxide (H₂O₂) generation during electro-Fenton oxidation, effects of pH, current density, molecular oxygen (O₂) flow rate, and anode material on H₂O₂ generation were evaluated. H₂O₂ generation was enhanced by increasing the current density up to 60 mA/cm² and the O₂ flow rate up to 80 mL/min at pH 3.0 and using carbon felt cathode and boron-doped diamond (BDD) anode. Electro-Fenton-BDD oxidation achieved the total CLQ depletion and 92% total organic carbon (TOC) removal. Electro-Fenton-BDD oxidation was more effective than electro-Fenton-Pt and anodic oxidation using Pt and BDD anodes. The efficiency of CLQ depletion by electro-Fenton-BDD oxidation raises by increasing the current density and Fe²⁺ dose; however it drops with the increase of pH and CLQ concentration. CLQ depletion follows a pseudo-first order kinetics in all the experiments. The identification of CLQ degradation intermediates by chromatography methods confirms the formation of 7-chloro-4-quinolinamine, oxamic, and oxalic acids. Quantitative amounts of chlorides, nitrates, and ammonium ions are released during electro-Fenton oxidation of CLQ. The high efficiency of electro-Fenton oxidation derives from the generation of hydroxyl radicals from the catalytic decomposition of H₂O₂ by Fe²⁺ in solution, and the electrogeneration of hydroxyl and sulfates radicals and other strong oxidants (persulfates) from the oxidation of the electrolyte at the surface BDD anode. Electro-Fenton oxidation has the potential to be an alternative method for treating wastewaters contaminated with CLQ and its derivatives.

Keywords: Boron-doped diamond; Chloroquine; Electro-fenton; H(2)O(2) generation; Hydroxyl radicals.

Fig. 1

Effects of (a) initial pH, (b) current density, (c) O₂ flow rate, and (d) anode material on the changes of H₂O₂ concentration with time during electrolysis of 0.05 M Na₂SO₄. Experimental conditions: (a) j = 60 mA/cm², O₂ flow rate = 80 mL/min, Anode: Pt (30 cm²), cathode: Carbon felt (30 cm²), T = 25 °C, stirring: 300 rpm; (b) pH = 3.0, O₂ flow rate = 80 mL/min, Anode: Pt (30 cm²), cathode: Carbon felt (30 cm²), T = 25 °C, stirring: 300 rpm; (c) j = 60 mA/cm², pH = 3.0, Anode: Pt (30 cm²), cathode: Carbon felt (30 cm²), T = 25 °C, stirring: 300 rpm (d) j = 60 mA/cm², pH = 3.0, O₂ flow rate = 80 mL/min, Anode: BDD/Pt/Graphite (30 cm²), cathode: Carbon felt (30 cm²), T = 25 °C, stirring: 300 rpm.

Fig. 2

Changes of CLQ concentration with time during electrochemical treatment of 125 mg/L CLQ aqueous solutions by anodic oxidation and electro-Fenton oxidation. Experimental conditions: Electrolyte: 0.05 M Na₂SO₄, j = 60 mA/cm², pH = 3.0, T = 25 °C, stirring = 300 rpm; Electrolysis-Pt: Anode: Pt, Cathode: Stainless steel; Electrolysis-BDD: Anode: BDD, Cathode: Stainless steel; Electro-Fenton-Pt: Anode Pt, Cathode: Carbon felt, O₂ flow rate: 80 mL/min, Fe²⁺: 10 mg/L; Electro-Fenton-BDD: Anode: BDD, Cathode: Carbon felt, O₂ flow rate: 80 mL/min, Fe²⁺: 10 mg/L.

Fig. 3

Changes of normalized concentration ([CLQ]_t/[CLQ]₀) with time (/[CLQ]₀ during electro-Fenton oxidation of 0.05 M Na₂SO₄ aqueous solutions containing different CLQ concentrations using carbon felt cathode and BDD anode. Inlet graph: the changes of pseudo-first order rate constant k_obsversus CLQ concentration. Experimental conditions: j = 60 mA/cm², pH = 3.0, O₂ flow rate = 80 mL/min, [Fe²⁺] = 10 mg/L, T = 25 °C, stirring = 300 rpm.

Fig. 4

Changes of: (a) CLQ concentration with time at different pH values during electro-Fenton oxidation of 125 mg/L CLQ aqueous solutions using carbon felt cathode and BDD anode, and (b) pseudo-first order rate constant k_obsversus initial pH. Experimental conditions: Electrolyte: 0.05 M Na₂SO₄, j = 60 mA/cm², O₂ flow rate = 80 mL/min, [Fe²⁺] = 10 mg/L, T = 25 °C, stirring = 300 rpm.

Fig. 5

Changes of CLQ concentration with time at different current densities (20–200 mA/cm²) during electro-Fenton oxidation of 125 mg/L CLQ aqueous solutions using carbon felt cathode and BDD anode. Inlet: pseudo-first order rate constant k_obsversus current density. Experimental conditions: Electrolyte: 0.05 M Na₂SO₄, pH = 3.0, O₂ flow rate = 80 mL/min, [Fe²⁺] = 10 mg/L, T = 25 °C, stirring = 300 rpm.

Fig. 6

Changes of: (a) CLQ concentration with time at different Fe²⁺ doses during electro-Fenton oxidation of 125 mg/L CLQ aqueous solutions using carbon felt cathode and BDD anode, and (b) pseudo-first order rate constant k_obsversus Fe²⁺ dose. Experimental conditions: Electrolyte: 0.05 M Na₂SO₄, j = 60 mA/cm², pH = 3.0, O₂ flow rate = 80 mL/min, T = 25 °C, stirring = 300 rpm.

Fig. 7

Changes with time of: (a) TOC and intermediates, (b) Chlorides and active chlorine, (c) Nitrogen intermediates, (d) organic intermediates during electro-Fenton oxidation of 125 mg/L CLQ aqueous solutions using carbon felt cathode and BDD anode. Experimental conditions: Electrolyte: 0.05 M Na₂SO₄, j = 60 mA/cm², pH = 3.0, O₂ flow rate = 80 mL/min, Fe²⁺ = 10 mg/L T = 25 °C, stirring = 300 rpm.

Fig. 8

Simple mechanism for CLQ degradation by electro-Fenton oxidation.