Photocatalytic Degradation of Diclofenac in Tap Water on TiO2 Nanotubes Assisted with Ozone Generated from Boron-Doped Diamond Electrode
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-05-12 |
| Journal | Catalysts |
| Authors | Daichuan Ma, Xianying Han, Xinsheng Li, Daibing Luo |
| Institutions | Beijing Institute of Petrochemical Technology, Sichuan University |
| Citations | 3 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research details the development and performance of a synergistic electrochemical-photocatalytic system (TiO2/O3/UV) for the efficient degradation of diclofenac in tap water.
- Core Innovation: The system utilizes a Hole-Arrayed Boron-Doped Diamond (HABDD) free-standing electrode to generate ozone (O3) in situ directly into the flowing water, which then assists the photocatalysis occurring on vertically aligned TiO2 nanotubes (TNTs).
- Performance Achievement: The combined TiO2/O3/UV route achieved 85.56% diclofenac removal (10 mg/L initial concentration) in 1 hour, significantly surpassing the efficiency of individual UV, O3, O3/UV, or TiO2/UV treatments.
- Mechanism Enhancement: O3 acts as an electron scavenger, capturing photo-generated electrons from the TiO2 conduction band. This effectively suppresses charge carrier recombination, increasing the lifetime of reactive holes (h+) and generating highly active Reactive Oxygen Species (ROS).
- Catalyst Structure: The TNTs, grown on a Ti mesh, exhibit a high BET surface area (269 m2/g) and anatase phase crystallinity, optimizing UV absorption and reaction sites.
- Electrode Durability: The HABDD electrode demonstrated ideal durability, maintaining stable O3 production rates (around 0.36 mg/min at 0.5 A) over a 25-hour working period, suitable for high-power operation.
- Theoretical Insight: Density Functional Theory (DFT) calculations confirmed that the bridging adsorption mode (TiO2=(OH)2-O3) is the most thermodynamically favorable for O3 on the anatase TiO2 (101) surface, promoting charge separation.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diclofenac Removal Efficiency | 85.56 | % | TiO2/O3/UV system (10 mg/L, 1 h). |
| Optimal Water Flow Rate | 150 | mL/min | Highest degradation efficiency achieved. |
| Maximum O3 Production Rate | 0.382 | mg/L | Generated in tap water at 0.5 A. |
| O3 Consumption Rate | 22.8 | mg/h | Required to achieve 85.56% removal. |
| Applied Current Range (O3 Gen) | 0.1 to 0.5 | A | Linear increase in O3 production observed. |
| UV Wavelength | 254 | nm | Incident UV lamp source. |
| TiO2 Nanotube Phase | Anatase | N/A | Characterized by XRD peaks (25.5°, 38.1°, 48.3°). |
| TiO2 Nanotube BET Area | 269 | m2/g | High surface area catalyst. |
| TiO2 Nanotube Internal Diameter | 60 ~ 100 | nm | Catalyst microstructure. |
| TiO2 Nanotube Film Thickness | 10 | ”m | Grown on Ti mesh substrate. |
| HABDD Hole Diameter | 0.5 (500) | mm (”m) | Micro hole structure for 3D reaction zone. |
| HABDD Thickness/Hole Depth | 1 | mm | Free-standing electrode dimension. |
| Favorable O3 Adsorption Energy (Ea) | -4.3352 | eV | For TiO2=(OH)2-O3 bridging mode (DFT calculation). |
Key Methodologies
Section titled âKey MethodologiesâThe synergistic system relies on the precise fabrication of both the HABDD electrode and the TiO2 nanotube catalyst, followed by continuous flow operation.
- HABDD Electrode Fabrication:
- Method: Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD, 2.45 GHz).
- Substrate: Ta plate (10 x 10 cm2) with pre-arrayed holes.
- Precursors: Acetone/Hydrogen gas mixture (Carbon source); Trimethyl borate (B(OCH3)3) (Boron dopant).
- Result: A free-standing diamond electrode with a uniform surface compacted with diamond microcrystals, expanding the reaction area from planar to sectional depth.
- TiO2 Nanotube Synthesis:
- Method: Electrochemical Anodization (20 h treatment).
- Electrodes: Ti mesh (Working Electrode); Pt plate (Counter Electrode).
- Electrolyte: Formamide (94.7 wt%), H2O (4.4 wt%), and NH4F (0.9 wt%).
- Result: Vertically aligned anatase TiO2 nanotubes on the Ti mesh substrate.
- Reactor Setup and Operation:
- Configuration: Continuous flowing mode reactor (Pyrex glass).
- Electrochemical Cell: HABDD anode (4 x 4 cm2) and Platinum mesh cathode, separated by Nafion film (solid-state electrolyte).
- Photocatalysis: TiO2 nanotube film (4 x 4 cm2) placed parallel to the HABDD, 2 cm apart.
- Energy Input: UV lamp (254 nm) illuminated the TiO2 film from behind.
- Process Flow: Diclofenac-containing tap water circulated through the system, passing the HABDD (O3 generation) and then the TiO2/UV zone (photocatalysis).
- Theoretical Modeling:
- Method: CASTEP (Cambridge serial total energy package) using Generalized Gradient Approximation (GGA) of Perdew and Wang (PW91).
- Goal: Calculate the final energy (Ea) of O3 adsorption models on the anatase TiO2 (101) surface to determine the most stable configuration for ROS generation.
Commercial Applications
Section titled âCommercial ApplicationsâThe technology developed, particularly the use of highly durable Boron-Doped Diamond (BDD) electrodes for in situ oxidant generation combined with high-surface-area photocatalysts, is highly relevant to advanced water purification sectors.
- Wastewater Treatment (WWT):
- Pharmaceutical Removal: Effective mineralization of persistent organic pollutants (POPs) and pharmaceutical residues (like diclofenac) from municipal and industrial effluents.
- Advanced Oxidation Processes (AOPs): Provides a robust, synergistic AOP system (Electrochemistry + Photocatalysis) that is more efficient than conventional methods.
- Drinking Water Purification:
- Suitable for treating trace contaminants in municipal drinking water lines, ensuring public health safety against low-concentration pharmaceuticals.
- High-Durability Electrochemistry:
- The HABDD free-standing electrode technology is ideal for high-power electrochemical applications requiring extreme corrosion resistance and long operational lifetimes, such as industrial electro-oxidation or electro-synthesis.
- Catalyst Manufacturing:
- The synthesis method for high-surface-area, vertically aligned TiO2 nanotubes on mesh substrates offers a scalable approach for producing efficient, reusable heterogeneous catalysts for flow reactors.
View Original Abstract
Degradation of pharmaceuticals in water by TiO2 photocatalysis often suffers from low efficiency due to low activity and mass transfer limitation. In this work, diclofenac removal in tap water was performed by photocatalysis on TiO2 nanotube growth on Ti mesh substrate assisted by ozone (O3), which was generated from a hole-arrayed boron-doped diamond (HABDD) film electrode. The vertically oriented TiO2 nanotubes were used as the heterogeneous photocatalyst. The HABDD, as a self-standing diamond electrode, was designed and custom-made by MWCVD technology. The microstructures and crystalline of the TiO2 nanotubes and HABDD were characterized by a scanning electronic micrograph (SEM) and X-ray diffraction (XRD). Unlike other ozone generation methods, direct generation of ozone in the flowing water was applied in the photocatalysis process, and its effect was discussed. The diclofenac removal performance of the electrochemical-photocatalytic system was studied depending on O3 generation efficiency, flowing rate, and the initial diclofenac concentration. The enhanced degradation effect from O3 molecules on TiO2 photocatalysis was attributed to the larger active surface area, the increased photo-generated charge separation rate, and the contact area of O3. The degradation efficiency in the combined electrochemical-photocatalytic TiO2/O3/UV system was higher than that of the O3/UV and TiO2/UV routes individually. Furthermore, a theoretical calculation was used to analyze the TiO2/O3 interface in aqueous media in terms of the final energy. This system created an almost in situ feeding channel of oxidants in the TiO2 photocatalysis process, thus increasing photocatalytic efficiency. This synergetic system is promising in the treatment of pharmaceuticals in water.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
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