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 |
Executive Summary
Section titled âExecutive SummaryâThis study successfully synthesized and optimized a high-performance Manganese Dioxide/Carbon Fiber (MnO2/CF) composite electrode for the electrosorptive removal of hexavalent chromium (Cr(VI)) ions from aqueous solutions.
- High Efficiency: The electrode achieved a maximum Cr(VI) removal efficiency of 99.99% from a 100 ppm solution under optimized conditions.
- High Capacity: The corresponding equilibrium adsorption capacity (qe) was determined to be 129.02 mg/g, demonstrating superior performance for heavy metal remediation.
- Optimized Conditions: The optimal operating parameters, determined using the Box-Behnken Design (BBD), were a cell voltage of 4.6 V, a pH of 2, and a NaCl concentration of 1.5 g/L.
- Synthesis Method: The MnO2 nanostructures were synthesized via a simple, galvanostatic anodic electrodeposition process onto activated carbon fiber (CF) at 0.3 mA/cm2.
- Material Structure: FESEM confirmed the formation of rod-like, nanostructured gamma-MnO2 (Îł-MnO2) particles, approximately 35.11 nm in diameter, which provide short diffusion channels and high surface area for enhanced electrosorption kinetics.
- Mechanism: The high removal rate (equilibrium reached in 3 hours) is attributed to the electrodeâs faradic-capacitive behavior, combining electrostatic adsorption (CDI) with redox reactions involving MnO2.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Electrode Type | MnO2/CF Composite | - | Working Electrode (Anode) |
| Synthesis Method | Anodic Electrodeposition | - | Galvanostatic, 4 hours |
| Synthesis Current Density | 0.3 | mA/cm2 | Applied during deposition |
| Synthesis Temperature | 90 | °C | Solution temperature |
| Initial Cr(VI) Concentration | 100 | mg/L | Electrosorption test concentration |
| Optimal pH (X1) | 2 | - | Determined by BBD optimization |
| Optimal Cell Voltage (X3) | 4.6 | V | Determined by BBD optimization |
| Optimal NaCl Conc. (X2) | 1.5 | g/L | Determined by BBD optimization |
| Maximum Removal Efficiency | 99.99 | % | Achieved at optimal conditions |
| Adsorption Capacity (qe) | 129.02 | mg/g | Achieved at optimal conditions |
| Equilibrium Time | 3 | hours | Time required for saturation |
| MnO2 Phase | Orthorhombic Îł-MnO2 | - | Confirmed by XRD (JCPDS NO.14-0644) |
| Nanostructure Morphology | Spherical brushes/Nanorods | - | Confirmed by FESEM |
| Average Nanorod Diameter | 35.11 | nm | Measured via FESEM |
| Model R2 (Determination Coeff.) | 99.42 | % | Indicates excellent model fit to experimental data |
Key Methodologies
Section titled âKey Methodologiesâ- Carbon Fiber (CF) Activation: Commercial CF substrate (16.5 cm x 5 cm) was chemically activated by immersion in 5% HNO3 solution for 30 minutes at 80 °C.
- MnO2 Electrodeposition: Nanostructured MnO2 was deposited onto the activated CF (anode) galvanostatically for 4 hours at a constant current density of 0.3 mA/cm2.
- Electrolyte Composition (Synthesis): The electrolytic solution used for deposition consisted of 0.64 M H2SO4 and 0.35 M MnSO4, maintained at 90 °C and agitated by a magnetic stirrer.
- Electrode Characterization: The composite electrode morphology and composition were analyzed using Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectrometry (EDX). Crystal structure was confirmed via X-ray Diffraction (XRD).
- Electrosorption Testing (CDI): Batch experiments were performed using the MnO2/CF composite as the working electrode and a stainless steel plate as the counter electrode, separated by 1.5 cm.
- Analytical Measurement: Cr(VI) concentration was determined using a UV spectrophotometer at 540 nm, relying on the colorimetric reaction with diphenylcarbazide in acidic media.
- Optimization Strategy: Response Surface Methodology (RSM) utilizing the Box-Behnken Design (BBD) was applied to model and optimize the effects and interactions of three variables (pH, NaCl concentration, and cell voltage) on Cr(VI) removal efficiency.
Commercial Applications
Section titled âCommercial ApplicationsâThe synthesized MnO2/CF composite electrode and the optimized electrosorption process are highly relevant for advanced water purification technologies, particularly those requiring high efficiency and low energy consumption.
- Industrial Wastewater Treatment: Direct application in treating effluents from industries such as electroplating, leather tanning, and chemical manufacturing, which are primary sources of toxic Cr(VI) contamination.
- Capacitive Deionization (CDI) Systems: The electrode serves as a high-performance component for CDI units, offering advantages over traditional carbon-only electrodes due to the enhanced pseudocapacitive behavior of the MnO2 coating.
- Heavy Metal Remediation: Applicable for the selective removal of various heavy metal oxyanions (like Cr(VI) and potentially arsenic) from contaminated water sources, leveraging the redox activity of MnO2.
- Electrochemical Energy Storage: The MnO2 nanostructure, known for its high theoretical pseudo capacitance (1370 F.g-1), makes this composite material suitable for development in high-rate supercapacitors and batteries.
- Electrochemical Sensor Technology: The high surface area and controlled nanostructure of the MnO2 coating could be utilized in developing sensitive electrochemical sensors for environmental monitoring.
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.