Anodic oxidation of paraquat herbicide on BDD electrode - comparative evaluation of variable effects and degradation mechanisms
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-01-01 |
| Journal | RSC Advances |
| Authors | Nejmeddine Rabaaoui, Naoufel Ben Hamadi, Mourad Cherif, Ahlem Guesmi, Wesam Abd ElâFattah |
| Institutions | Tunis University, Tunis El Manar University |
| Citations | 1 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis study rigorously compared Boron-Doped Diamond (BDD), Lead Dioxide (PbO2), and Platinum (Pt) anodes for the electrochemical degradation of the persistent herbicide paraquat.
- Superior Performance: BDD anodes demonstrated exceptional efficiency, achieving 99% Chemical Oxygen Demand (COD) removal and 98.6% Total Organic Carbon (TOC) removal within 300 minutes, significantly outperforming PbO2 (88.5%) and Pt (79.5%).
- Mechanism Confirmation: The high efficiency is attributed to BDDâs capability to generate highly reactive, physisorbed hydroxyl radicals (âOH), enabling non-selective, deep mineralization.
- Kinetics and Mineralization: Degradation followed pseudo-first-order kinetics with a high rate constant (k = 1.53 x 10-2 s-1), confirming rapid initial oxidative transformation. Full mineralization into CO2, H2O, and NH4+ was confirmed via intermediate tracking.
- Operational Optimization: Optimal conditions were identified as acidic pH (pH 3.0) and a current density of 15 mA cm-2, balancing high efficiency with moderate energy consumption.
- Sustainability and Durability: BDD exhibited negligible corrosion (less than 10-5 g cm-2 h), ensuring long-term structural integrity, a key advantage over the substantially degrading PbO2 anode (0.0335 g cm-2 h).
- Energy Metrics: Despite high initial Faradaic Efficiency (FE) (70.14% at 220 min), the Cumulative Energy Consumption (CEC) reached 66 kWh m-3, highlighting the need to optimize treatment duration to avoid excessive energy expenditure in low-efficiency phases.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| COD Removal (BDD) | 99 | % | 300 min, 15 mA cm-2, pH 3.0 |
| TOC Removal (BDD) | 98.6 | % | 300 min (from 25 mg L-1 to 0.40 mg L-1) |
| Kinetic Rate Constant (k) | 1.53 x 10-2 | s-1 | Pseudo-first-order degradation |
| Optimal Current Density | 15 | mA cm-2 | Balance of efficiency and energy input |
| Optimal pH | 3.0 | - | Promotes âOH radical generation |
| BDD Corrosion Rate | <10-5 | g cm-2 h | Negligible corrosion |
| PbO2 Corrosion Rate | 0.0335 | g cm-2 h | Substantial degradation observed |
| Initial Paraquat Conc. | 30 | mg L-1 | Electrolysis starting concentration |
| Electrolyte Conc. | 50 | mmol L-1 | Used Na2SO4, NaCl, or NaNO3 |
| Electrolysis Temperature | 20 | °C | Controlled operating temperature |
| Anode Effective Area | 10 | cm2 | BDD, PbO2, and Pt anodes (2.5 cm x 4 cm) |
| Faradaic Efficiency (FE) | 70.14 | % | Measured at 220 minutes |
| Cumulative Energy Cons. (CEC) | 66.00 | kWh m-3 | Measured at 220 minutes |
| BDD Film Thickness | ~1 | ”m | Synthesized via HF-CVD |
| BDD Resistivity | 15 (±30%) | mΩ cm | Electrical property of the diamond film |
Key Methodologies
Section titled âKey MethodologiesâThe study employed galvanostatic electrochemical advanced oxidation processes (EAOPs) using three distinct anode materials.
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BDD Electrode Synthesis (Hot Filament Chemical Vapor Deposition - HF-CVD):
- Substrate: Conductive p-Si (1 mm, Siltronix).
- Filament Temperature: Maintained between 2440 °C and 2560 °C.
- Substrate Temperature: Monitored at 830 °C.
- Reactive Gas: 1% Methane (CH4) in Hydrogen (H2), containing 1-3 ppm of trimethyl boron (dopant).
- Gas Flow Rate: 5 mL min-1, resulting in a growth rate of 0.24 ”m h-1.
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PbO2 Electrode Preparation:
- Method: Galvanostatic electrochemical anodization.
- Substrate: Pretreated lead.
- Electrolyte: Oxalic acid solution (100 g L-1).
- Conditions: 30 minutes at ambient temperature, 100 mA cm-2 anodic current density.
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Electrolysis Setup and Operation:
- Cell Type: Single-compartment cylindrical cell, thermostated at 20 °C.
- Anodes: BDD, PbO2, and Pt, each with a 10 cm2 effective geometric surface area.
- Cathode: Cylindrical graphite rod (0.8 cm diameter, 4.0 cm immersed length).
- Electrolyte: Various 50 mmol L-1 solutions (Na2SO4, NaCl, NaNO3) were tested.
- Analysis: Paraquat and intermediates were quantified using HPLC-Thermo Fisher Scientific equipped with a Diode Array Detector (DAD). Mineralization was tracked via COD and TOC analysis.
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Mechanistic Analysis:
- Aromatic and carboxylic acid intermediates (e.g., monopyridone, oxalic acid, formic acid) were identified using HPLC and Mass Spectrometry (MS) to map the multi-stage degradation pathway, confirming ring-opening and final mineralization.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings of this research, particularly the robust performance and durability of Boron-Doped Diamond (BDD) electrodes, are highly relevant for industrial sectors dealing with persistent organic pollutants (POPs).
| Application Area | Relevance to Technology |
|---|---|
| Wastewater Treatment (Industrial Effluents) | BDD anodes provide deep mineralization capacity, essential for treating refractory organic contaminants (like herbicides, pesticides, and pharmaceuticals) that resist conventional biological or chemical methods. |
| Pesticide Manufacturing/Formulation | Direct application for treating highly concentrated wastewater streams generated during the production of quaternary ammonium herbicides (e.g., paraquat). |
| Water Reuse and Discharge Compliance | The ability to achieve near-complete TOC removal and convert toxic intermediates into harmless inorganic end-products (CO2, H2O, NH4+) ensures compliance with strict regulatory standards for water discharge or reuse. |
| Advanced Oxidation Processes (AOPs) | BDD electrodes are a core component in sustainable EAOPs, offering superior oxidative power and operational stability compared to traditional electrode materials (PbO2, Pt). |
| Electrochemical Sensor Technology | The use of BDD substrates, known for their wide potential window and stability, is foundational for developing highly sensitive electrochemical sensors for detecting environmental contaminants. |
View Original Abstract
Anodic oxidation of paraquat on BDD electrodes achieves up to 99% COD and 98.6% TOC removal. A detailed mechanistic pathway via aromatic ring cleavage and carboxylic acids confirms efficient mineralization despite increasing energy demand.