Electrosorption of Hexavalent Chromium Ions by MnO2/Carbon Fiber Composite Electrode - Analysis and Optimization of the Process by Box-Behnken Design
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-03-29 |
| Journal | Iraqi Journal of Chemical and Petroleum Engineering |
| Authors | Zainab M. Issa, Rasha H. Salman, Prashant Basavaraj Bhagawati |
| Institutions | University of Baghdad |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Advanced Electrochemical Water Treatment
Section titled âTechnical Documentation & Analysis: Advanced Electrochemical Water TreatmentâExecutive Summary
Section titled âExecutive SummaryâThis documentation analyzes the research on using a nanostructured Manganese Dioxide ($\text{MnO}_{2}$)/Carbon Fiber (CF) composite electrode for the electrosorption of hexavalent chromium ($\text{Cr}(\text{VI})$) ions. This application falls under advanced electrochemical water treatment, a field where 6CCVDâs Boron-Doped Diamond (BDD) materials offer superior performance and longevity.
- Core Application: Highly efficient removal of toxic hexavalent chromium ($\text{Cr}(\text{VI})$) from aqueous solutions via the electrosorption (Capacitive Deionization, CDI) method.
- Material Synthesis: Nanostructured $\text{MnO}{2}$ was galvanostatically electrodeposited onto a Carbon Fiber substrate, confirmed to form rod-like $\gamma$-$\text{MnO}{2}$ nanorods (35.11 nm diameter).
- Performance Metric: Achieved an exceptional $\text{Cr}(\text{VI})$ removal efficiency of 99.99% and an adsorption capacity of 129.0194 mg/g.
- Optimization: The process parameters (pH, NaCl concentration, and cell voltage) were rigorously optimized using Response Surface Methodology (RSM) and Box-Behnken Design (BBD).
- Optimal Conditions: Maximum removal was achieved under highly acidic conditions: pH 2, cell voltage 4.6 V, and NaCl concentration 1.5 g/L.
- 6CCVD Value Proposition: While the paper uses carbon fiber, 6CCVD specializes in Boron-Doped Diamond (BDD), the ultimate carbon electrode material, offering superior stability and efficiency for harsh electrochemical environments like those required for $\text{Cr}(\text{VI})$ reduction.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental results and optimization analysis:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optimal $\text{Cr}(\text{VI})$ Removal Efficiency ($\text{Re}%$) | 99.99 | % | Achieved under BBD optimal conditions. |
| Maximum Adsorption Capacity ($\text{q}_{\text{e}}$) | 129.0194 | mg/g | At 100 mg/L initial $\text{Cr}(\text{VI})$ concentration. |
| Optimal Cell Voltage ($\text{X}_{3}$) | 4.6 | V | Optimized parameter for electrosorption. |
| Optimal pH ($\text{X}_{1}$) | 2 | - | Highly acidic environment required for cathodic reduction of $\text{Cr}(\text{VI})$. |
| Optimal NaCl Concentration ($\text{X}_{2}$) | 1.5 | g/L | Ionic strength optimization. |
| $\text{MnO}_{2}$ Nanorod Diameter | 35.11 | nm | Determined via FESEM analysis. |
| Electrodeposition Current Density | 0.3 | $\text{mA}/\text{cm}^{2}$ | Used for $\text{MnO}_{2}$ synthesis onto CF. |
| Electrodeposition Time | 4 | h | Time to reach equilibrium saturation. |
| Initial $\text{Cr}(\text{VI})$ Concentration ($\text{C}_{0}$) | 100 | $\text{mg}/\text{l}$ | Used for BBD experimental design. |
| Model Determination Coefficient ($\text{R}^{2}$) | 99.42 | % | Indicating excellent model fit with experimental data. |
Key Methodologies
Section titled âKey MethodologiesâThe experiment involved the synthesis of the composite electrode and the optimization of the electrosorption process using statistical design.
- Carbon Fiber (CF) Activation: A rectangular CF slice (16.5 cm x 5 cm) was activated by soaking for 30 minutes at 80 °C in 5% $\text{HNO}_{3}$.
- Electrolyte Preparation: The electrolytic solution (1.8 L) consisted of 0.64 M $\text{H}{2}\text{SO}{4}$ and 0.35 M $\text{MnSO}_{4}$, maintained at 90 °C under agitation.
- Anodic Electrodeposition: $\text{MnO}_{2}$ was galvanostatically deposited onto the activated CF (anode) for 4 hours at a constant current density of 0.3 $\text{mA}/\text{cm}^{2}$.
- Electrode Characterization:
- Morphology: Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray Spectrometry (EDX) (operating at 25 kV and 100 ”A).
- Crystal Structure: X-ray Diffraction (XRD) using $\text{Cu}-\text{K}\alpha$ radiation ($\lambda = 1.54056 \text{A}^{\circ}$) confirmed the formation of orthorhombic $\gamma$-$\text{MnO}_{2}$.
- Electrosorption Setup (CDI): A batch system used the $\text{MnO}_{2}$/CF composite as the working electrode and a stainless steel plate (17 cm x 5 cm x 3 mm) as the counter electrode, separated by 1.5 cm.
- Optimization Design: Response Surface Methodology (RSM) via Box-Behnken Design (BBD) was employed to analyze the effects and interactions of three variables ($\text{X}{1}$: pH, $\text{X}{2}$: NaCl concentration, $\text{X}_{3}$: cell voltage) on the $\text{Cr}(\text{VI})$ removal efficiency ($\text{Y}$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research demonstrates the effectiveness of electrochemical methods for heavy metal remediation, particularly in harsh, acidic environments (optimal pH 2). While the $\text{MnO}_{2}$/Carbon Fiber composite performs well, the long-term stability and efficiency of such systems are often limited by the inherent properties of carbon fiber.
6CCVD specializes in MPCVD Diamond, offering Boron-Doped Diamond (BDD) electrodes that are the gold standard for extreme electrochemical applications, providing superior stability and performance for replicating or extending this research.
| Research Requirement/Challenge | 6CCVD Advanced Diamond Solution | Technical Advantage |
|---|---|---|
| Electrode Stability in Harsh Environments (Optimal pH 2, high voltage) | Boron-Doped Diamond (BDD) Plates | BDD possesses the widest electrochemical potential window of any known material, resisting corrosion and degradation in highly acidic or oxidative conditions far better than carbon fiber or metal oxides. This ensures long-term operational stability and reduced maintenance costs for $\text{Cr}(\text{VI})$ reduction systems. |
| Need for High Surface Area Electrode (Paper used porous CF and nanorods) | Polycrystalline Diamond (PCD) Wafers | 6CCVD supplies heavy Boron-Doped PCD, which can be engineered with textured surfaces or used as robust substrates for catalyst deposition (e.g., $\text{MnO}_{2}$ or other transition metal oxides), providing high active surface area while leveraging diamondâs stability. |
| Custom Electrode Dimensions (Paper used specific 16.5 cm x 5 cm slices) | Custom Dimensions and Thickness | We provide custom plates and wafers up to 125 mm (PCD) and substrates up to 10 mm thick, precisely tailored to fit any CDI stack, flow cell, or reactor geometry required for industrial scale-up. |
| Reliable Electrical Contact (Required for 4.6 V operation) | Integrated Metalization Services | 6CCVD offers in-house metalization capabilities (Au, Pt, Pd, Ti, W, Cu) to create robust, low-resistance ohmic contacts directly on the BDD surface, ensuring efficient current delivery for high-performance electrosorption. |
| Surface Quality for Deposition (For uniform $\text{MnO}_{2}$ film) | Precision Polishing (Ra < 1 nm SCD, < 5 nm PCD) | We offer ultra-smooth Single Crystal Diamond (SCD) surfaces for highly controlled thin-film deposition, or precision-polished PCD for applications requiring a balance of surface area and uniformity. |
Engineering Support
Section titled âEngineering SupportâThe successful optimization of this $\text{Cr}(\text{VI})$ removal process highlights the critical role of material selection in electrochemical water treatment. 6CCVDâs in-house $\text{PhD}$ team specializes in electrochemistry and material science and can assist researchers and engineers in transitioning from conventional carbon materials to high-performance BDD for similar heavy metal remediation, advanced oxidation processes (AOPs), or CDI projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
A nano manganese dioxide (MnO2) was electrodeposited galvanostatically onto a carbon fiber (CF) surface using the simple method of anodic electrodeposition. The composite electrode was characterized by field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD). Very few studies investigated the efficiency of this electrode for heavy metals removal, especially chromium. The electrosorption properties of the nano MnO2/CF electrode were examined by removing Cr(VI) ions from aqueous solutions. NaCl concentration, pH, and cell voltage were studied and optimized using the Box-Behnken design (BDD) to investigate their effects and interactions on the electrosorption process. The results showed that the optimal conditions for the removal of Cr(VI) ions were a cell voltage of 4.6 V, pH of 2 and NaCl concentration of 1.5 g/L. This work indicated that MnO2/CF electrode was highly effective in removing Cr(VI) ions and the BBD approach was a feasible and functional method for evaluating the experimental data.