| Metadata | Details |
|---|
| Publication Date | 2022-07-14 |
| Journal | Applied Catalysis B: Environmental |
| Authors | Jing Ma, Clément Trellu, Nihal Oturan, Stéphane Raffy, Mehmet A. Oturan |
| Institutions | Université Gustave Eiffel, Saint-Gobain (France) |
| Citations | 24 |
| Analysis | Full AI Review Included |
This study investigates the development and performance of porous Ti/TiOx foam electrodes, synthesized via a scalable plasma spraying technique, for the removal of organic pollutants from water using electrochemical advanced oxidation processes (EAOPs).
- Enhanced Kinetics: Ti/TiOx Foam 1 demonstrated significantly enhanced degradation kinetics for Paracetamol (PCT) and Terephthalic Acid (TA) in a stirred-tank reactor, achieving 1.5 times (PCT) and 2.4 times (TA) faster rates compared to a standard Ti/TiOx plate.
- Mass Transport Dominance: The improved performance of Foam 1 is primarily attributed to its coarse surface roughness (Effective Roughness Factor, ERF = 1.54), which enhances mass transport conditions even in a stirred-tank configuration.
- Flow-Through Superiority: When tested in a flow-through configuration, Foam 1 achieved a PCT degradation kinetic rate 3.9 times higher than the Ti/TiOx plate and 1.9 times higher than the Boron-Doped Diamond (BDD) plate, confirming the benefit of convective-enhanced mass transport.
- Structure-Reactivity Correlation: The porous structure of the Ti substrate dictates the coating homogeneity and, consequently, the reaction mechanism:
- Foam 1 (Finer pores): Homogeneous TiOx coating, promoting high Oxygen Evolution Potential (OEP) and OH-mediated oxidation, leading to higher mineralization (34% TOC removal in 2h).
- Foam 2 (Coarser pores): Heterogeneous TiOx coating with exposed Ti, resulting in lower OEP and favoring Direct Electron Transfer (DET), leading to fast initial degradation but poor mineralization and accumulation of toxic by-products.
- Material Composition: The primary electroactive phase of the coating across all materials was identified as highly conductive Magnéli phase Ti4O7.
| Parameter | Value | Unit | Context |
|---|
| Foam 1 Median Pore Size | 15 | ”m | Hg porosimetry (surface area) |
| Foam 2 Pore Size Range | 0.7 - 1.6 | mm | Optical microscopy |
| Foam 1 Porosity | 35 | % | - |
| Ti/TiOx Plate EASA | 2200 | cm2 | Electroactive Surface Area |
| Foam 1 EASA | 1620 | cm2 | Electroactive Surface Area |
| Foam 1 Roughness Factor (RF) | 69 | - | Ratio EASA/Sgeo |
| Foam 2 Effective Roughness Factor (ERF) | 4.18 | - | Calculated at diffusion layer thickness (Ύ) = 30 ”m |
| Ti/TiOx Plate OEP | 2.78 | V vs Ag/AgCl/3 M KCl | Oxygen Evolution Potential |
| Foam 1 OEP | 2.82 | V vs Ag/AgCl/3 M KCl | High OEP, suitable for OH generation |
| Foam 2 OEP | 2.26 | V vs Ag/AgCl/3 M KCl | Low OEP, favors O2 evolution |
| Foam 1 PCT k1 Enhancement (Flow-through) | 3.9 | times | Compared to Ti/TiOx plate (stirred-tank) |
| Foam 1 Mineralization Yield (2h) | 34 | % | PCT TOC removal (stirred-tank) |
| BDD Mineralization Yield (2h) | 66 | % | PCT TOC removal (reference) |
| Plasma Torch Voltage | 63 - 66 | V | Plasma spraying synthesis |
| Plasma Torch Current | 600 | A | Plasma spraying synthesis |
| TiOx Powder Particle Size | 30 | ”m | Used for plasma injection |
| Stirred-Tank Current Density | 5 | mA cm-2 | Applied during electro-oxidation |
- Substrates: Three types of Ti substrates were used: a 2 mm thick TA6V plate, Porous Ti Foam 1 (American Elements), and Porous Ti Foam 2 (SELEE).
- Coating Material: Electro-fused TiOx powder (average particle size 30 ”m).
- Plasma Generation: Saint-Gobain pro plasma torch supplied with mixed gas:
- Argon (Ar): 45 L min-1
- Hydrogen (H2): 11 L min-1
- Voltage/Current: 63-66 V / 600 A.
- Injection: TiOx powder injected using Argon carrier gas (4 L min-1 flow rate).
- Deposition: Spray distance set at 110 mm; coating deposited on both sides of the substrates under an argon shield to prevent reoxidation.
- Chemical Composition (Bulk): X-Ray Diffraction (XRD) confirmed the major phase as highly conductive Magnéli phase Ti4O7, with minor phases (Ti6O11, Ti8O15).
- Surface Composition: Raman spectroscopy confirmed the presence of Ti4O7 and Rutile TiO2 (at higher laser irradiation).
- Morphology and Thickness: Scanning Electron Microscopy (SEM) was used to observe porous structure and coating distribution (Foam 1 coating thickness: ~30 ”m; Foam 2 coating thickness: 0 to ~60 ”m).
- Pore Structure:
- Foam 1: Hg porosimetry (median pore size 15 ”m).
- Foam 2: Digital optical microscopy (pore size 0.7-1.6 mm).
- Reactor Setup: Cylindrical undivided glass cell (300 mL solution) operated in batch mode (stirred-tank) or flow-through mode (continuous recirculation).
- Electrode Configuration: Ti/TiOx material as anode; Carbon felt (stirred-tank) or perforated Ti (flow-through) as cathode.
- Electrochemical Characterization:
- Reactivity (OER): Linear Sweep Voltammetry (LSV) used to determine Oxygen Evolution Potential (OEP).
- Electroactive Surface Area (EASA): Cyclic Voltammetry (CV) used to estimate double layer capacitance, calculating EASA and Roughness Factor (RF).
- Mass Transfer Coefficient (km): Limiting current technique using the ferro-ferricyanide redox couple.
- Probe Molecules:
- Terephthalic Acid (TA): Probe for OH-mediated oxidation (reacts slowly via DET).
- Oxalic Acid (OA): Probe for Direct Electron Transfer (DET) (reacts slowly with OH).
- Model Pollutant & Quenching: Paracetamol (PCT) degradation studied with quenchers:
- Ethanol (EtOH): Quencher for both OH and Sulfate Radicals (SO4âą-).
- Tert-Butyl Alcohol (TBA): Quencher primarily for OH.
The developed porous Ti/TiOx foam electrodes are highly relevant for industrial applications requiring efficient and scalable electrochemical water treatment, particularly where mass transport limitations are critical.
| Industry/Sector | Application Focus | Technical Advantage |
|---|
| Wastewater Treatment | Removal of persistent organic pollutants (POPs) and micropollutants (e.g., pharmaceuticals like PCT). | High degradation kinetics (up to 3.9x enhancement) achieved via convective mass transport in flow-through reactors. |
| Industrial Water Recycling | Treatment of complex industrial effluents containing recalcitrant compounds. | Scalable manufacturing via plasma spraying allows for large-scale electrode production and integration into industrial systems. |
| Electrochemical Reactor Design | Development of high-performance reactive electrochemical membranes (REMs) or flow-through cells. | Foams with larger pore sizes (like Foam 1) offer the advantage of reduced fouling issues and lower pressure drop compared to materials with very fine pores. |
| Advanced Oxidation Processes (AOPs) | Systems requiring efficient generation of hydroxyl radicals (OH) for non-selective oxidation and high mineralization yields. | Foam 1 structure ensures homogeneous TiOx coating and high OEP, promoting OH generation necessary for complete mineralization. |
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- 2018 - An overview on the removal of synthetic dyes from water by electrochemical advanced oxidation processes [Crossref]
- 2019 - Environmental applications of boron-doped diamond electrodes: 1. Applications in water and wastewater treatment [Crossref]
- 2021 - Electrochemical technologies for the treatment of pesticides
- 2014 - Advanced oxidation processes in water/wastewater treatment: principles and applications. A review [Crossref]
- 2017 - Electrochemical advanced oxidation processes: a review on their application to synthetic and real wastewaters [Crossref]
- 2009 - Electrochemical oxidation of organic pollutants in water at metal oxide electrodes: a simple theoretical model including direct and indirect oxidation processes at the anodic surface [Crossref]
- 2021 - Magnetic heterojunction of oxygen-deficient Ti3+-TiO2 and Ar-Fe2O3 derived from metal-organic frameworks for efficient peroxydisulfate (PDS) photo-activation [Crossref]