Sensing of chemical oxygen demand (COD) by amperometric detection—dependence of current signal on concentration and type of organic species
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2023-05-02 |
| Journal | Environmental Monitoring and Assessment |
| Authors | Samira Lambertz, Marcus Franke, Michael Stelter, Patrick Braeutigam |
| Institutions | Friedrich Schiller University Jena |
| Citations | 9 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: BDD for Chemical Oxygen Demand (COD) Sensing
Section titled “Technical Documentation & Analysis: BDD for Chemical Oxygen Demand (COD) Sensing”Executive Summary
Section titled “Executive Summary”This research validates the use of Boron-Doped Diamond (BDD) electrodes for the fast, non-toxic, and environmentally friendly amperometric determination of Chemical Oxygen Demand (COD) in water monitoring applications.
- Core Achievement: Demonstrated a viable electrochemical alternative to traditional, toxic K2Cr2O6 methods for COD measurement.
- Mechanism Validation: The method relies on the electrochemical formation of highly reactive hydroxyl radicals (BDD(OH)) on the BDD surface, which subsequently oxidize organic compounds.
- Linear Working Range: A compound-independent linear working range of 25-150 mg/L COD was established, suitable for many environmental monitoring applications.
- Kinetic Limitation Identified: Above 150 mg/L COD, the current signal becomes highly dependent on the specific organic species present, indicating electrode saturation where hydroxyl radical generation (k1) becomes the rate-determining step relative to organic species concentration (k2CR).
- Optimization Pathway: To extend the linear working range and achieve compound-independent measurement at higher concentrations, the ratio of hydroxyl radicals to organic species must be increased, primarily by maximizing the BDD active surface area (e.g., using porous electrodes or custom geometries).
- 6CCVD Value Proposition: 6CCVD specializes in the custom fabrication of high-quality BDD films and substrates, offering the precise material engineering (doping, geometry, surface area) required to overcome the identified kinetic limitations and optimize next-generation COD sensors.
Technical Specifications
Section titled “Technical Specifications”The following hard data points were extracted from the experimental setup and results:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electrode Material | Boron-Doped Diamond (BDD) | N/A | Working Electrode (WE) |
| BDD Thickness | 5 | µm | Diamond layer on Niobium substrate |
| Electrode Diameter | 8 | mm | Working Electrode geometry |
| Counter Electrode | Platinum (Pt) wire | N/A | Diameter 0.5 mm, Length 10 mm |
| Reference Electrode | Ag/AgCl (3 M NaCl) | N/A | Standard reference electrode |
| Electrolyte Composition | 0.1 M Na2SO4 + 0.1 mM H2SO4 | N/A | Used for measurements |
| Activation Potential | 3.0 | V | vs Ag/AgCl (3 M NaCl) for 30 s |
| Measurement Potential | 2.4 | V | vs Ag/AgCl (3 M NaCl) for 170 s |
| Stirring Speed | 100 | rpm | Mechanical stirring during measurement |
| Compound-Independent Linear Range | 25-150 | mg/L COD | Low concentration regime (k1 >> k2CR) |
| Detection Limit | 25 | mg/L COD | Lower bound of the linear range |
| Precision (Linear Range) | 30 | % | Calculated as p = sy/m * 100% |
Key Methodologies
Section titled “Key Methodologies”The amperometric determination of COD utilized a three-electrode cell setup connected to a potentiostat.
- Electrolyte Preparation: The electrochemical cell (17 ml volume) was filled with 12 ml of electrolyte (0.1 M Na2SO4 and 0.1 mM H2SO4).
- Stirring Initiation: The solution was stirred at a constant speed of 100 rpm.
- Electrode Activation: An activation step was performed at a potential of 3.0 V vs Ag/AgCl (3 M NaCl) for 30 seconds.
- Measurement Potential Application: The potential was subsequently set to 2.4 V vs Ag/AgCl (3 M NaCl) for 170 seconds.
- Sample Addition: After a 110-second waiting period, 5 ml of the organic sample solution was added to the cell.
- Signal Acquisition: The current measured at 2.4 V was recorded.
- Data Processing: The raw current-time curve was processed using a KNIME® workflow, including smoothing (moving average window length of 20) and background current subtraction, to calculate the reduced signal current.
- Substances Tested: Six diverse organic compounds were tested across a wide range (10 mg/L to 10,000 mg/L COD): Ascorbic acid, Acetic acid, Glucose, Malonic acid, Sucrose, and Citric acid.
6CCVD Solutions & Capabilities
Section titled “6CCVD Solutions & Capabilities”The research highlights the critical role of BDD electrode kinetics and surface area in achieving reliable, compound-independent COD sensing. 6CCVD is uniquely positioned to supply the advanced BDD materials and custom engineering services necessary to replicate this work and extend the linear working range for industrial applications.
Applicable Materials
Section titled “Applicable Materials”To replicate and advance this research, 6CCVD recommends the following materials:
- Heavy Boron-Doped PCD/SCD: Highly conductive BDD films are essential for maximizing the overpotential required for efficient hydroxyl radical (BDD(OH)) formation. We provide films with precise doping levels to ensure optimal electrochemical performance and stability.
- Custom Substrates: The paper used BDD on Niobium. 6CCVD offers BDD films grown on various conductive substrates, including Niobium, Silicon, or highly conductive PCD substrates (up to 125 mm diameter).
Customization Potential
Section titled “Customization Potential”The paper explicitly suggests increasing the electrode surface area (e.g., using a porous working electrode) or reducing the sample volume (e.g., thin film cell) to improve the hydroxyl radical/organic compound ratio and extend the linear working range beyond 150 mg/L COD. 6CCVD directly addresses these optimization needs:
| Research Optimization Requirement | 6CCVD Capability | Technical Advantage for COD Sensing |
|---|---|---|
| Increased Surface Area: Need for porous or high surface area electrodes to increase k1 (hydroxyl radical formation rate). | Custom Thickness & Geometry: We supply SCD and PCD plates/wafers up to 125 mm in diameter. We can engineer structured or rough surfaces (PCD Ra < 5 nm, SCD Ra < 1 nm) or thicker substrates (up to 10 mm) to maximize active electrochemical area within the cell volume. | Directly extends the compound-independent linear range by increasing the rate-determining step (k1) relative to the organic concentration (CR). |
| Thin Film Cell Design: Need for minimal sample volume to maintain a high hydroxyl radical/organic compound ratio. | Precision Laser Cutting & Custom Dimensions: We provide BDD wafers cut to precise, small dimensions (e.g., 8 mm diameter discs used in the paper) or custom micro-geometries required for thin film or microfluidic electrochemical cells. | Enables high-throughput, low-volume, real-time monitoring systems suitable for industrial wastewater control. |
| Electrode Integration: Need for robust, low-resistance electrical contacts. | In-House Metalization Services: We offer custom metalization layers (Au, Pt, Pd, Ti, W, Cu) applied directly to the BDD surface, ensuring reliable electrical connection for amperometric measurements. | Guarantees long-term sensor stability and minimizes contact resistance, crucial for accurate current signal measurement. |
Engineering Support
Section titled “Engineering Support”6CCVD’s in-house team of PhD material scientists and electrochemists can assist researchers and engineers in selecting the optimal BDD material specifications (doping concentration, surface roughness, and geometry) for similar Wastewater Monitoring and COD Sensing projects. We provide consultation on how to leverage MPCVD diamond properties to overcome kinetic limitations and achieve superior sensor performance.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.