Heterogeneous Model To Distinguish the Activity of Electrogenerated Chlorine Species from Soluble Chlorine in an Electrochemical Reactor

Reaction Mechanism of Oxytetracycline Degradation by Electrogenerated Reactive Chlorine: The Influence of Current Density and pH

A binary dimensionally stable anode Ti/TiO2-RuO2 electrode was used to abate the antibiotic oxytetracycline (OTC) (C22H24N2O9) in chloride water. The anode was prepared using the Pechini method and subsequently characterized by X-ray diffraction, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), and cyclic voltammetry (CV). The optimum values of the operational parameters affecting removal efficiency were determined using a 2 × 3 factorial design by screening j (6.0, 10, and 20 A m-2) and pH (3, 6.5, and 10). The textural analysis revealed the formation of active oxides (RuO2 and TiO2 coating rutile-type P42/mnm, space group 136), with a cracked surface and good dispersion of metal components. A contour graph verified that the most suitable condition for contaminant degradation was 20 A m-2 at a circumneutral pH of 6.5, resulting in approximately 97% degradation after 20 min of electrolysis according to pseudo-first-order reaction kinetics and the loss of the antibiotic activity of OTC. In addition, the results of oxidant formation and CV indicate that the best electrochemical activation of the anode to form Cl2-active mainly depended on pH. Liquid chromatography-mass spectrometry (LC-MS) and density functional theory were employed to propose a reaction pathway for OTC degradation. Three byproducts with m/z 426, 256, and 226 were identified corresponding to the removal of amide and amine groups, which are susceptible sites to electrophilic attack by active chlorine species. The findings from this work stand out for prospective applications of anodic electrochemical oxidation to efficiently eliminate antibiotics with similar chemical structures in wastewater containing chlorides.

Electrochemical HOCl Production Modeling for an Electrochemical Catheter

Hypochlorous acid (HOCl) is a strong oxidizing agent that damages cells by interacting with lipids, nucleic acids, sulfur-containing amino acids, and membrane components. It is an endogenous substance produced by the immune system to protect mammals from pathogens. Previously, we developed an HOCl-generating electrochemical catheter (e-catheter) and demonstrated its ability to prevent central line-associated bloodstream infections. The e-catheter is an electrochemical system consisting of two parts - an e-hub and a tube. Working, counter, and reference electrodes are placed in the e-hub, which contains 0.9% NaCl as an electrolyte. Although a prototype of this device has shown activity against pathogens, it is helpful to understand the factors influencing associated electrochemical/chemical processes to optimize design and efficacy. A mathematical model could predict factors influencing HOCl generation and distribution in the catheter and could aid in optimizing these devices. Here, we developed an Electrochemical Hypochlorous Acid Production (EHAP) model to predict factors influencing electrochemical generation and distribution of HOCl in e-catheters, including polarization time, diffusion of HOCl into the e-catheter, operational voltage, working electrode length, and surface area.

Dynamic chloride ion adsorption on single iridium atom boosts seawater oxidation catalysis

Seawater electrolysis offers a renewable, scalable, and economic means for green hydrogen production. However, anode corrosion by Cl- pose great challenges for its commercialization. Herein, different from conventional catalysts designed to repel Cl- adsorption, we develop an atomic Ir catalyst on cobalt iron layered double hydroxide (Ir/CoFe-LDH) to tailor Cl- adsorption and modulate the electronic structure of the Ir active center, thereby establishing a unique Ir-OH/Cl coordination for alkaline seawater electrolysis. Operando characterizations and theoretical calculations unveil the pivotal role of this coordination state to lower OER activation energy by a factor of 1.93. The Ir/CoFe-LDH exhibits a remarkable oxygen evolution reaction activity (202 mV overpotential and TOF = 7.46 O2 s-1) in 6 M NaOH+2.8 M NaCl, superior over Cl--free 6 M NaOH electrolyte (236 mV overpotential and TOF = 1.05 O2 s-1), with 100% catalytic selectivity and stability at high current densities (400-800 mA cm-2) for more than 1,000 h.

An alternative approach to the kinetic modeling of pharmaceuticals degradation in high saline water by electrogenerated active chlorine species

A semiempirical approach considering the rate of reactive chlorine species-RCS- production (Φ_E) as a function of current and Cl^- concentration for the modeling of acetaminophen (ACE) degradation is presented. A filter-press reactor having a Ti/RuO₂-ZrO₂ (Sb₂O₃ doped) anode, NaCl (0.04-0.1 mol L^-1) as supporting electrolyte, and operated in continuous mode, was considered. A current of 100 mA and a flow of 11 mL min^-1 favored the electrogeneration of RCS and ACE degradation. Hydraulic retention time and Φ_E were the most relevant parameters for the RCS production. These two parameters, plus the pollutant concentration, were very determinant for the ACE degradation. The model successfully reproduced the ACE removal in distilled water at different concentrations (10, 20, 40, and 60 mg L^-1). The electrochemical system achieved removals between 80 and 100% of ACE in distilled water. The ACE treatment in actual seawater (a chloride-rich matrix, 0.539 mol L^-1 of Cl^-) was assessed, and the degradation was simulated using the developed model. The competing role toward electrogenerated RCS by intrinsic organic matter (3.2 mg L^-1) in the seawater was a critical point, and the simulated values fitted well with the experimental data. Finally, the action of the electrochemical system on ciprofloxacin (CIP) in real seawater and its antimicrobial activity was tested. CIP removal (100% at 120 s) was faster than that observed for ACE (100% of degradation after 180 s) due to CIP has amine groups that are more reactive toward RCS than phenol moiety on ACE. Moreover, the system removed 100% of the antimicrobial activity associated with CIP, indicating a positive environmental effect of the treatment.

Modeling the sulfamethoxazole degradation by active chlorine in a flow electrochemical reactor

The aim of this study is to propose a continuous physicochemical model accounting for the active chlorine production used to degrade recalcitrant sulfamethoxazole (SMX) in an electrochemical flow reactor. The computational model describes the fluid mechanics and mass transfer occurring in the re/actor, along with the electrode kinetics of hydrogen evolution reaction arising on a stainless steel cathode, and the chloride oxidation on a DSA. Specifically, the anodic contributions assume the heterogeneous nature of the adsorbed chlorine species formed on this surface, which are a model requirement to correctly define the experimental reactor performance and degradation efficiency of the contaminant. The experimental validation conducted at different applied current densities, volumetric flows, and chloride concentrations is adequately explained by the model, thus evidencing some of the phenomena controlling the electrocatalytic chlorine production for environmental applications. The best conditions to eliminate the SMX are proposed based on the theoretical analysis of the current efficiency calculated with the model, and experimentally confirmed. The use of the Ti/RuO₂-ZrO₂-Sb₂O₃ anode at the bench scale improves the SMX removal by using electro-generated chlorine species adsorbed on its surface, which remarkably increases the oxidation potential of the system along with chlorine desorbed from the electrode. This is a technological innovation concerning other mediated oxidation methods entirely using oxidants in solution.