Synergetic effect in water treatment with mesoporous TiO2/BDD hybrid electrode
At a Glance
Section titled “At a Glance”| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | RSC Advances |
| Authors | Norihiro Suzuki, Akihiro Okazaki, Haruo Kuriyama, Izumi Serizawa, Yuki Hirami |
| Institutions | North Bengal University, Tokyo University of Science |
| Citations | 17 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled “Executive Summary”- Core Technology: Fabrication and testing of a mesoporous Titanium Dioxide (TiO2)/Boron-Doped Diamond (BDD) hybrid electrode designed for integrated Advanced Oxidation Processes (AOPs).
- Mechanism Integration: The hybrid system simultaneously utilizes BDD’s wide potential window for high-voltage water electrolysis (generating O3, H2O2, and OH•) and TiO2’s photocatalytic activity under deep-UV irradiation (222 nm).
- Synergetic Effect Demonstrated: A significant synergetic effect was observed during Methylene Blue (MB) decomposition using the hybrid electrode under photoelectrochemical conditions, where the total degradation rate was greater than the sum of the individual photocatalytic and electrochemical rates.
- Mechanistic Insight: The synergy is primarily attributed to photoexcited electrons (ecb-) in the TiO2 conduction band preferentially reducing electrochemically generated Hydrogen Peroxide (H2O2) to highly potent Hydroxyl Radicals (OH•).
- BDD Role: BDD maintains a wide potential window, enabling the high-voltage electrolysis necessary for O3 production (Standard Oxidation Potential: 2.07 V vs. NHE) and subsequent H2O2 formation.
- Efficiency Note: The hybrid electrode produced less O3 gas than pure BDD due to reduced exposed BDD surface area, but the enhanced OH• generation pathway compensated, leading to superior overall water treatment efficacy.
Technical Specifications
Section titled “Technical Specifications”| Parameter | Value | Unit | Context |
|---|---|---|---|
| Hydroxyl Radical (OH•) Potential | 2.80 | V vs. NHE | Standard oxidation potential (highest oxidant) |
| Ozone (O3) Potential | 2.07 | V vs. NHE | Standard oxidation potential |
| Hydrogen Peroxide (H2O2) Potential | 1.77 | V vs. NHE | Standard oxidation potential |
| BDD Band Gap | 5.5 | eV | Corresponds to 225 nm UV excitation |
| UV Irradiation Wavelength | 222 | nm | Deep-UV excimer lamp source used for TiO2/BDD excitation |
| UV Intensity | 1.2 | mW cm-2 | Applied during photoelectrochemical tests |
| Electrolyte Composition | 0.25 | M | Phosphate aqueous buffer solution |
| Electrolyte pH | 6.8 | - | Maintained during experiments |
| Comparative Operating Current | 75 | mA | Selected constant current for water treatment tests |
| H2O2 Concentration (Hybrid @ 75 mA) | ~1.2 | ppm | Dissolved H2O2 detected after 10 min electrolysis |
| O3 Gas Production (Hybrid @ 75 mA) | ~0.15 | ppm | O3 gas detected from the glass cell outlet |
| MB Initial Concentration (C0) | 20 | µM | Methylene Blue used as model pollutant |
Key Methodologies
Section titled “Key Methodologies”- Electrode Synthesis: Mesoporous TiO2 layer was deposited onto the BDD substrate using a surfactant-assisted sol-gel method.
- Electrochemical Setup: Experiments utilized an H-type glass cell, separating the working electrode (BDD or hybrid) and the counter electrode (Pt) via a Nafion® NRE-212 membrane to prevent reduction by hydrogen gas.
- Electrochemical Analysis: Cyclic voltammograms (CV) were measured in 0.25 M phosphate buffer (pH 6.8). Current-voltage relationships were determined using a potentiostat/galvanostat.
- Ozone (O3) Detection: Constant current (50, 75, or 100 mA) was applied for 3 min while N2 gas purged the solution. O3 gas was collected in Tedlar® bags and quantified using a Kitagawa gas detector tube system.
- Hydrogen Peroxide (H2O2) Quantification: H2O2 formed after 10 min of electrolysis was quantified using a coloring reaction involving KI and ammonium molybdate, forming I3-, which was measured spectrophotometrically at 350 nm.
- Photoelectrochemical Treatment: Methylene Blue (MB) solution (20 µM) was treated under constant stirring. The hybrid electrode was simultaneously subjected to a constant current (75 mA) and deep-UV irradiation (222 nm, 1.2 mW cm-2).
- Mechanism Confirmation: Formic acid (a sacrificial reagent) was added to the MB solution during photocatalysis to react with valence band holes (hvb+), confirming that the primary oxidation pathway in the hybrid system shifts from hole oxidation to electron-driven reduction of H2O2 to OH•.
Commercial Applications
Section titled “Commercial Applications”- Wastewater Treatment (AOPs): Implementation of compact, integrated AOP systems for the efficient decomposition of recalcitrant organic pollutants (e.g., dyes, pesticides, pharmaceuticals) that are resistant to conventional ozone or UV treatment alone.
- Industrial Effluent Remediation: Targeting highly stable toxic chemicals, such as perfluorooctanoic acid (PFOA) and other persistent organic pollutants (POPs), using the high oxidative power of electrochemically-assisted OH• generation.
- Decentralized Water Purification: Developing simpler and more compact water treatment units suitable for remote or decentralized applications, leveraging the combined functionality of the hybrid electrode.
- Electrochemical Disinfection: Utilizing the high-voltage BDD component for effective deactivation of water-borne pathogens, enhancing the system’s utility beyond chemical decomposition.
- Advanced Electrode Manufacturing: Production of nanostructured composite electrodes (BDD/Metal Oxide) where the BDD substrate provides the necessary wide potential window and stability for high-performance electrochemical catalysis.
View Original Abstract
A mesoporous TiO<sub>2</sub>/BDD hybrid electrode showed a synergetic effect between electrochemical water treatment and photocatalytic water treatment.