Insight into electrochemical degradation of Cartap (in Padan 95SP) by boron-doped diamond electrode - kinetic and effect of water matrices
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2022-01-01 |
| Journal | TURKISH JOURNAL OF CHEMISTRY |
| Authors | HOANG NGUYEN |
| Institutions | Da Nang University of Technology, University of Da Nang |
| Citations | 2 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- Core Technology: Electrochemical oxidation (EO) using a Boron-Doped Diamond (BDD) electrode was successfully applied for the degradation of Cartap (a persistent pesticide found in Padan 95SP).
- Mechanism Dominance: The degradation proceeded via a dual mechanism: 85% indirect oxidation by reactive oxygen species (ROS) and 15% Direct Electron Transfer (DET). Hydroxyl radicals (•OH) were the primary oxidant, accounting for 61.5% of the total removal.
- Electrode Performance: The BDD electrode, characterized by a 2.5-3 µm diamond layer and 15.1% Boron content (EDX), demonstrated good conductivity with a charge transfer resistance (Rct) of 92.6 Ω.
- Matrix Enhancement (Cl-): The presence of 15 mM chloride (Cl-) significantly enhanced the degradation rate constant (kCT) by 38%, attributed to the formation of highly reactive chlorine species (RCS).
- Matrix Inhibition (HCO3-/HA): Common water matrices acted as scavengers: 15 mM bicarbonate (HCO3-) reduced kCT by 74%, and 15 mg L-1 humic acid (HA) reduced kCT by 64%, necessitating matrix management for field applications.
- Kinetic Modeling: A quadratic relationship was proposed linking the apparent degradation rate constant (kCT) to the applied current density (j), aiding in reactor optimization.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Anode Material | BDD on Si | - | Working electrode |
| BDD Layer Thickness | 2.5-3 | µm | - |
| BDD Grain Size (Medium) | ~200 | nm | - |
| Charge Transfer Resistance (Rct) | 92.6 | Ω | BDD electrode (vs. Pt: 13 Ω) |
| Applied Current Density (j) | 10 to 40 | mA cm-2 | Galvanostatic control range |
| Optimal pH | 3 | - | Electrolysis condition |
| Initial Cartap Concentration | 40 | µM | - |
| •OH Contribution | 61.5 | % | Total degradation pathway |
| SO4•- Contribution | 12.8 | % | Total degradation pathway |
| DET Contribution | 15 | % | Total degradation pathway |
| Steady-State [•OH]ss | 3.2 x 10-13 | M | Calculated concentration |
| Steady-State [SO4•-]ss | 5.8 x 10-14 | M | Calculated concentration |
| B Content (EDX) | 15.1 | % | Elemental composition |
| kCT Increase (15 mM Cl-) | 38 | % | Enhancement effect |
| kCT Reduction (15 mM HCO3-) | 74 | % | Inhibition effect |
| kCT Reduction (15 mg L-1 HA) | 64 | % | Inhibition effect |
| O2 Evolution Potential (LSV) | 1.6 | V | At 50 mV s-1 scan rate |
Key Methodologies
Section titled “Key Methodologies”- Electrode Fabrication & Characterization: A commercial BDD electrode (Neocoat, Switzerland) on a Si substrate was used. Characterization included Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX) for morphology and composition, X-ray Diffraction (XRD) for crystal structure (confirming diamond cubic phase), and Electrochemical Impedance Spectroscopy (EIS) to determine charge transfer resistance.
- Electrochemical Setup: Experiments were conducted in a 400 mL undivided cell at 22 °C. The BDD (3.8 cm2) served as the working anode, with a Platinum foil (2 cm2) counter electrode and an Ag/AgCl reference electrode.
- Electrolysis Conditions: Galvanostatic control was maintained, varying the current density (j) from 10 to 40 mA cm-2. The supporting electrolyte was 0.05 M Na2SO4, and the pH was maintained at 3.
- Kinetic Measurement: Cartap concentration was determined spectrophotometrically using the Ellman’s reagent (DTNB) procedure, measuring the generated yellow anions at 412 nm.
- Radical Quantification (Scavenging):
- Methanol (MeOH) and tert-butanol (TBA) were used as radical scavengers to differentiate the contributions of •OH and SO4•-.
- Nitrobenzene (NB) and Benzoic Acid (BA) were used as probe compounds, measured by HPLC, to calculate the steady-state concentrations of [•OH]ss and [SO4•-]ss.
- Matrix Effect Study: The influence of common water matrices (HCO3-, Cl-, and Humic Acid (HA)) on the degradation kinetics was investigated by varying their concentrations up to 15 mM or 15 mg L-1.
Commercial Applications
Section titled “Commercial Applications”The findings support the application of BDD electrochemical oxidation in advanced water treatment, particularly for recalcitrant organic contaminants.
- Wastewater Treatment (Pesticides and POPs):
- Effective destruction of persistent organic pollutants (POPs) like Cartap, offering a high-efficiency solution for agricultural and industrial wastewater streams.
- BDD anodes provide a stable, corrosion-resistant alternative to conventional electrodes (e.g., IrO2, Pt) for mineralization processes.
- Advanced Oxidation Processes (AOPs):
- Implementation of BDD-based AOPs where high concentrations of powerful oxidants (•OH, SO4•-) are required, minimizing sludge production compared to Fenton processes.
- Water Reuse and Remediation:
- Applicable in treating complex water matrices (e.g., saline or brackish water where high Cl- concentration is beneficial) for municipal or industrial water reuse schemes.
- BDD Electrode Manufacturing (6ccvd.com Relevance):
- The results validate the performance of BDD films on silicon substrates for high-current density electrochemical applications, confirming the necessity of high Boron doping levels (15.1% B content) for efficient radical generation.
- The kinetic data provides essential design parameters for scaling up BDD reactor systems for commercial deployment.
View Original Abstract
In this work, the kinetic electrochemical degradation of Cartap (CT) (in Padan 95 SP) at boron-doped diamond (BDD) electrode was investigated. This study indicated that the degradation of CT underwent both direct and indirect oxidations. Water matrices can either accelerate or inhibit the removal efficiency of CT: adding 15 mM Cl<sup>-</sup> improved <i>k</i><i><sub>CT</sub></i> from 0.039 min<sup>-1</sup> to 0.054 min<sup>-1</sup> (increased by 38%), while <i>k</i><i><sub>CT</sub></i> decreased by 61.5% and 64% when increasing the concentration of HCO<sub>3</sub><sup>-</sup> and humic acid (HA) to 15 mM and 15 mg L<sup>-1</sup>, respectively. CT degradation was inhibited in the presence of methanol (MeOH) and <i>tert</i>-butanol (TBA) due to the scavenging effect of those chemicals toward reactive species. The contribution of reactive oxidants was calculated as: DET (direct electron transfer) accounted for 15%; •OH accounted for 61.5%; SO<sub>4</sub><sup>•-</sup> accounted for 12.8%; ROS (the other reactive oxygen species) accounted for 8.5%. The transformation pathways of major reactive species were established.