Boosted Electrocatalytic Degradation of Levofloxacin by Chloride Ions - Performances Evaluation and Mechanism Insight with Different Anodes

At a Glance

Metadata	Details
Publication Date	2024-01-31
Journal	Molecules
Authors	Keda Yang, Peiwei Han, Yinan Liu, Hongxia Lv, Xiaofei Chen
Institutions	Beijing Institute of Petrochemical Technology, Tiandi Science & Technology (China)
Citations	13
Analysis	Full AI Review Included

Executive Summary

This research investigates the mechanism and performance enhancement of electrocatalytic degradation of Levofloxacin (LVX) in wastewater using three different anode materials: Boron-Doped Diamond (BDD), Titanium Suboxide (Ti₄O₇), and Ruthenium-Titanium (Ru-Ti), specifically focusing on the influence of chloride ions (Cl^-).

Core Value Proposition: Chloride ions, typically considered inhibitors or sources of unwanted byproducts, were found to significantly boost the degradation and mineralization efficiency of LVX, particularly on the Ti₄O₇ and Ru-Ti anodes.
Performance Enhancement: The Ti₄O₇ electrode showed the most dramatic improvement, increasing LVX conversion from 26% (without Cl^-) to nearly 100% within 30 minutes upon Cl^- addition.
Mechanism Insight: Electron Paramagnetic Resonance (EPR) confirmed that Cl^- participation enhances the generation of both hydroxyl radicals (•OH) and active chlorine species (Cl₂, HOCl, OCl^-), which synergistically drive the degradation process.
Electrochemical Tuning: Linear Sweep Voltammetry (LSV) demonstrated that Cl^- concentration directly affects the Oxygen Evolution Potential (OEP) of the anodes, thereby controlling the formation rate of the highly oxidative •OH radicals.
Optimal Conditions: Optimal Total Organic Carbon (TOC) removal was achieved at 4‰ Cl^- concentration for the Ti₄O₇ anode and 8‰ Cl^- for the Ru-Ti anode, indicating material-specific tolerance and radical pathway utilization.
Engineering Implication: The findings provide a theoretical foundation for designing highly chlorine-resistant electrocatalytic anodes suitable for the efficient treatment of saline organic wastewater, such as hospital or pharmaceutical effluent.

Technical Specifications

Parameter	Value	Unit	Context
Initial LVX Concentration	100	mg/L	Model wastewater concentration
Applied Current Density	39.6	A/m²	Electrocatalytic degradation condition
Supporting Electrolyte	3% Na₂SO₄	%	Used in all reaction groups
Optimal Cl^- (Ti₄O₇ TOC)	4	‰	Highest TOC removal efficiency
Optimal Cl^- (Ru-Ti TOC)	8	‰	Highest TOC removal efficiency
LVX Conversion (Ti₄O₇ w/ Cl^-)	~100	%	Achieved in 30 min
LVX Conversion (Ti₄O₇ w/o Cl^-)	26	%	Achieved in 30 min
BDD Synthesis Temperature	850	°C	Chemical Vapor Deposition (CVD)
BDD Synthesis Time	720	min	CVD reaction duration
Ti₄O₇ Reduction Temperature	850	°C	Reduction in N₂/H₂ mixture
Ti₄O₇ Deposition Power	200	W	Plasma-enhanced CVD
Ti₄O₇ Deposition Pressure	53.2	Pa	Plasma-enhanced CVD
Ti₄O₇ OEP (Optimal 4‰ Cl^-)	~2.5	V vs. SCE	Highest Oxygen Evolution Potential
Ru-Ti OEP (0‰ Cl^-)	~1.8	V vs. SCE	Oxygen Evolution Potential (OEP decreases with increasing Cl^-)

Key Methodologies

The study employed rigorous electrode preparation and advanced analytical techniques to evaluate performance and elucidate the reaction mechanism.

Electrode Preparation:
- Ru-Ti Electrodes: Purchased commercially (Baoji Aike Metals).
- BDD Electrodes: Prepared via Chemical Vapor Deposition (CVD) on a Si substrate at 850 °C for 720 minutes, using a gas mixture of CH₄ (2 mL/min), H₂ (98 mL/min), and B₂H₆ (0.2 mL/min) at 3 KPa pressure.
- Ti₄O₇ Electrodes: TiO₂ deposited on an 80 mm Ti plate using plasma-enhanced CVD (200 W power, 53.2 Pa pressure, 0 °C deposition temperature). Subsequently reduced in a mixture of N₂ and H₂ (1 L/min total flow) at 850 °C to form the Magnéli phase Ti_nO_2n-1.
Electrocatalytic Degradation Setup:
- Reactor: 200 mL model LVX wastewater (100 mg/L) circulated at 50 mL/min.
- Configuration: Three-electrode system (Anode: BDD, Ti₄O₇, or Ru-Ti; Cathode: Ru-Ti).
- Conditions: Reaction solution stirred at 300 r/min, maintained with 3% Na₂SO₄ supporting electrolyte, and operated at a constant current density of 39.6 A/m².
Characterization and Analysis:
- Structural Analysis: X-ray Diffraction (XRD) confirmed crystal structures (e.g., BDD (111) and (220) planes; Ti₄O₇ triclinic phase; Ru-Ti matching RuO₂ and TiO₂).
- Morphology: Scanning Electron Microscopy (SEM) analyzed surface structures (e.g., porous Ti₄O₇, rod-like Ru-Ti).
- Electrochemical Performance: Linear Sweep Voltammetry (LSV) measured the Oxygen Evolution Potential (OEP) to assess the barrier for •OH generation.
- Radical Detection: Electron Paramagnetic Resonance (EPR) spectroscopy, using DMPO as a spin trap, monitored the generation of hydroxyl radicals (•OH) and chlorine radicals.
- Efficiency Metrics: LVX conversion measured by High-Performance Liquid Chromatography (HPLC). Mineralization efficiency measured by Total Organic Carbon (TOC) analysis.

Commercial Applications

The findings regarding chloride-boosted electrocatalysis are highly relevant for industrial wastewater treatment, particularly in sectors dealing with persistent organic pollutants (POPs) and saline effluents.

Saline Wastewater Treatment: Applicable to industrial streams containing high concentrations of salts (chlorides), such as those generated by chemical manufacturing, textile dyeing, or marine aquaculture operations.
Pharmaceutical and Hospital Effluent Treatment: Provides a robust method for the complete mineralization (high TOC removal) of stable antibiotics like Levofloxacin, minimizing the release of active pharmaceutical ingredients (APIs) and antibiotic resistance genes (ARGs) into the environment.
Advanced Oxidation Processes (AOPs): Enables the design and deployment of highly efficient electrocatalytic reactors utilizing chlorine-resistant anodes (like optimized Ti₄O₇) for enhanced radical generation in complex matrices.
Electrode Manufacturing: Focuses development efforts on Magnéli phase titanium suboxide (Ti_nO_2n-1) anodes, confirming their superior performance and stability in chloride-rich environments compared to traditional BDD or Ru-Ti systems under these specific conditions.

View Original Abstract

As chloride (Cl−) is a commonly found anion in natural water, it has a significant impact on electrocatalytic oxidation processes; yet, the mechanism of radical transformation on different types of anodes remains unexplored. Therefore, this study aims to investigate the influence of chlorine-containing environments on the electrocatalytic degradation performance of levofloxacin using BDD, Ti4O7, and Ru-Ti electrodes. The comparative analysis of the electrode performance demonstrated that the presence of Cl− improved the removal and mineralization efficiency of levofloxacin on all the electrodes. The enhancement was the most pronounced on the Ti4O7 electrode and the least significant on the Ru-Ti electrode. The evaluation experiments and EPR characterization revealed that the increased generation of hydroxyl radicals and active chlorine played a major role in the degradation process, particularly on the Ti4O7 anode. The electrochemical performance tests indicated that the concentration of Cl− affected the oxygen evolution potentials of the electrode and consequently influenced the formation of hydroxyl radicals. This study elucidates the mechanism of Cl− participation in the electrocatalytic degradation of chlorine-containing organic wastewater. Therefore, the highly chlorine-resistant electrocatalytic anode materials hold great potential for the promotion of the practical application of the electrocatalytic treatment of antibiotic wastewater.

Tech Support

Original Source

DOI: https://doi.org/10.3390/molecules29030662

References

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