Electrochemical Degradation of Naproxen (NPX) and Diclofenac (DFC) through Active Chlorine Species (Cl₂-active): Considerations on Structural Aspects and Degradation in Urine

Abstract

The electrochemical degradation of two highly consumed analgesics, naproxen (NPX) and diclofenac (DFC), mediated by chloride ions and using a dimensionally stable anode (Ti/IrO2), is compared. In the first part, the ability of the system to generate reactive chlorine species was evaluated as a function of the current density (j= 1.25, 3.13, 5.00 mA cm-2) and the chloride concentration ([NaCl]= 0.01, 0.025, 0.05 mol L-1). Subsequently, under proper conditions, the process performance to degrade the pharmaceuticals individually and mixed, in distilled water and synthetic fresh urine, was evaluated. The electrochemical system achieved 100 % of NPX and DFC elimination in distilled water at 0.017 and 0.056 Ah L-1, respectively. A strong dependence on the chemical structure of the analgesic was evidenced in the degradation kinetics. Finally, slow elimination of the pharmaceuticals in the urine was observed, because of compounds in this complex matrix that compete for the degrading agents.

Indirect electrochemical degradation of acetaminophen: process performance, pollutant transformation, and matrix effects evaluation

“…The high accumulation of oxidizing species was related to the oxidation of chloride toward chlorine (Equations 1-4) on the Ti/IrO2 anode surface, plus the hydrolysis of chlorine molecules to produce hypochlorous acid and hypochlorite anion (Equations 5-6). On the other hand, the utilized anode cannot oxidize sulfate ions, but this induces oxidation of water, producing the oxygen evolution (as denoted by Equations 7-9) [21]. It should be mentioned that the oxygen evolution on our DSA is diminished in the presence of chloride and favored by the sulfate ion [24], [25].…”

“…Nevertheless, some inherent disadvantages (e.g., acidic pH requirements, catalysts addition and recovery, metal complexation, high electric energetic demand, or long UV exposure time [8], [12], [13]) limit the application of these methods. A promising alternative is the indirect oxidation by electrogenerated reactive chlorine species (RCS, 𝐶𝐶𝐶𝐶 2 , 𝐸𝐸°: 1.36 V; 𝐻𝐻𝐻𝐻𝐶𝐶𝐶𝐶, 𝐸𝐸°: 1.49 V; and 𝐻𝐻𝐶𝐶𝐶𝐶 − , 𝐸𝐸°: 0.89 V), which can be used to treat micropollutants and persistent contaminants (such as analgesics) in aqueous matrices [14]- [21]. The RCS act as oxidizing agents, and they have lower potentials than other oxidants (hydroxyl radical or sulfate radical), which makes RCS more selective for the attack to organic pollutants [14], [15], [17], [22], [23].…”

Electrochemical Technologies to Decrease the Chemical Risk of Hospital Wastewater and Urine

“…The presence of significant amounts of chloride ions in the effluent promoted the electrochemical production of free chlorine by anodic oxidation, which improved the degradation of the antibiotic by an indirect oxidation mechanism. The same experimental set-up and electrodes materials (Ti/IrO 2 anode and zirconium spiral cathode) were used by [86]. In this case, they studied the simultaneous degradation of diclofenac (40 µM) and naproxen (40 µM) in urine at 5 mA cm −2 and pH 6.0.…”

“…Molecules 2021, 26, x FOR PEER REVIEW 15 of 24 ode) were used by [86]. In this case, they studied the simultaneous degradation of diclofenac (40 μM) and naproxen (40 μM) in urine at 5 mA cm −2 and pH 6.0.…”