Research on the mechanism and reaction conditions of electrochemical preparation of persulfate in a split-cell reactor using BDD anode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | RSC Advances |
| Authors | Feng Zhang, Zhiyu Sun, Jianguo Cui |
| Institutions | Taiyuan University of Technology |
| Citations | 41 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the mechanism and optimization of persulfate (PDS, S2O82-) synthesis using a Boron-Doped Diamond (BDD) anode in a split-cell reactor, focusing on efficient sulfate recycling from wastewater.
- BDD Advantage: The BDD anodeâs wide electrochemical potential window and high oxygen-evolution potential significantly improve the current efficiency (CE) of PDS synthesis compared to traditional Pt electrodes, eliminating the need for oxygen evolution inhibitors.
- Dual Synthesis Mechanism: PDS formation proceeds via two confirmed pathways: (1) Indirect oxidation mediated by hydroxyl (âOH) radicals, which generate sulfate radicals (SO4.-); and (2) Direct electron transfer from sulfate/bisulfate ions (SO42-/HSO4-) on the electrode surface, generating SO4.-.
- Concentration Criticality: When the impressed current exceeds the limiting current density, increasing the sulfate electrolyte concentration (up to 0.8 mol L-1 tested) is crucial for maximizing PDS output and current efficiency.
- Thermal Control: Electrolysis temperature must be strictly controlled below 40 °C to prevent the thermal decomposition of PDS, which significantly reduces output and efficiency.
- pH Flexibility: The initial pH has a weak effect on PDS synthesis, though acidic conditions (pH 3-5) are slightly favorable. This is advantageous for treating acidic sulfate wastewater without requiring additional pH regulation.
- Current Density Scaling: PDS output increases linearly with current density. High current densities (60-120 mA cm-2) maintain high CE, while low current densities (30 mA cm-2) suffer from competing oxygen evolution side reactions.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| PDS Standard Redox Potential (EÂș) | 2.01 | V | Oxidation power |
| BDD Anode Substrate | Tantalum (Ta) | N/A | Electrode base material |
| BDD Film Thickness | 5 | ”m | Polycrystalline diamond film |
| Boron Doping Concentration | 2500 | ppm | BDD electrode specification |
| Optimal Temperature (Max) | <40 | °C | To prevent PDS thermal decomposition |
| CV Scan Range | -2.2 to 2 | V | vs. Saturated Calomel Electrode (SCE) |
| CV Scan Rate | 100 | mV s-1 | Electrochemical testing |
| Typical Current Density Range | 30 to 120 | mA cm-2 | Tested range for PDS synthesis |
| Electrolyte Concentration Range | 0.2 to 0.8 | mol L-1 | Na2SO4 tested range |
| Estimated Max Current Efficiency | >78 | % | Projected for 2 mol L-1 Na2SO4 at 120 mA cm-2 |
| Anode/Cathode Dimensions | 25 x 50 x 1 | mm | BDD (Ta-based) and Pt electrodes |
| Anode Electrolyte Flow Rate | 30 | mL min-1 | Circulation pump rate |
Key Methodologies
Section titled âKey Methodologiesâ- Split-Cell Reactor Design: A custom H-type reactor (100 mL effective volume) was employed, separating the BDD anode and Pt cathode using a Nafion-115 cation exchange membrane to prevent PDS reduction at the cathode.
- Electrolyte Circulation: Anode and cathode electrolytes were circulated independently between the cell and 250 mL storage tanks at a constant flow rate of 30 mL min-1, ensuring uniform concentration and temperature (25 ± 2 °C).
- Electrochemical Characterization (CV): Cyclic Voltammetry was performed using the BDD electrode as the working electrode (vs. SCE) to analyze the oxidation potential and electron transfer behavior of sulfate ions.
- Radical Identification (ESR): Electron Spin Resonance spectroscopy utilized 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a trapping agent to confirm the generation of both hydroxyl (âOH) and sulfate (SO4.-) radicals during electrolysis.
- Mechanism Quantification (Competitive Trapping): Carbamazepine (CBZ) was used as a probe molecule. Methanol (MeOH) (scavenges both âOH and SO4.-) and tert-Butyl Alcohol (TBA) (primarily scavenges âOH) were added to quantify the relative contribution of the indirect (âOH-mediated) versus direct (SO4.-) PDS synthesis pathways.
- PDS Measurement: Persulfate concentration was determined using an improved iodimetry method coupled with UV-vis spectrophotometry, measuring the triiodide ion (I3-) absorption at 352 nm.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology leverages the high efficiency and stability of BDD anodes for generating powerful oxidants, primarily targeting environmental and industrial chemical synthesis sectors.
- Wastewater Treatment (AOPs):
- In situ generation of PDS for Advanced Oxidation Processes (AOPs) to degrade refractory organic pollutants in industrial effluents.
- Treatment of high-concentration sulfate wastewater (e.g., acid mine drainage, pharmaceutical, and food industry effluents) by recycling sulfate into valuable PDS oxidant.
- Industrial Chemical Synthesis:
- Preparation of persulfate salts (e.g., sodium persulfate) without the need for traditional oxygen evolution inhibitors (like NH4+ or SCN-), leading to higher purity PDS products and reduced separation costs.
- Electrode Technology:
- Deployment of Tantalum-based Boron-Doped Diamond (BDD) electrodes in harsh electrochemical environments requiring high corrosion resistance and wide potential windows.
- Resource Recovery:
- Sustainable recycling of sulfate waste streams into a high-value chemical oxidant, reducing raw material costs and environmental discharge pollution.
View Original Abstract
Through cyclic voltammetry (CV) curve, electron spin resonance spectroscopy (ESR) characterization and free radical competitive trapping experiment, an analysis was performed on the mechanism of persulfate (PDS) electro-synthesis by sulfate at boron-doped diamond (BDD) anode.