Photocatalytic Degradation of Diclofenac in Tap Water on TiO2 Nanotubes Assisted with Ozone Generated from Boron-Doped Diamond Electrode

At a Glance

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

Technical Documentation & Analysis: MPCVD Diamond for Advanced Oxidation Processes

Reference Paper: Photocatalytic Degradation of Diclofenac in Tap Water on TiO₂ Nanotubes Assisted with Ozone Generated from Boron-Doped Diamond Electrode. Catalysts 2023, 13, 877.

Executive Summary

This research successfully demonstrates a highly efficient, synergistic electrochemical-photocatalytic system (TiO₂/O₃/UV) for the degradation of diclofenac, a persistent pharmaceutical pollutant, utilizing custom Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD) diamond.

Core Component: A custom-made, free-standing Hole-Arrayed Boron-Doped Diamond (HABDD) electrode was fabricated via MPCVD to serve as a robust, high-durability anode.
Synergistic AOP: The HABDD electrode enabled the direct, in situ generation of ozone (O₃) in flowing tap water, creating an efficient oxidant feeding channel that significantly boosted photocatalytic activity.
High Efficiency: The combined TiO₂/O₃/UV system achieved a maximum diclofenac removal efficiency of 85.56% in 1 hour, substantially surpassing the performance of individual UV, O₃, or TiO₂/UV routes.
Exceptional Durability: The HABDD electrode demonstrated ideal long-term stability, maintaining a consistent O₃ production rate (~0.36 mg/min) over a 25-hour continuous high-power operation (0.5 A).
Structural Optimization: The 3D holey framework (500 µm diameter holes) of the BDD electrode expanded the active reaction zone, improving ion transport and mass transfer kinetics.
Mechanism Confirmation: Theoretical calculations confirmed that O₃ adsorption on the anatase TiO₂ (101) surface, particularly via the Ti-O-H-O bridging mode, is thermodynamically favorable and enhances photo-generated charge separation.

Technical Specifications

The following hard data points were extracted from the experimental results detailing the performance and physical characteristics of the HABDD electrode and the AOP system.

Parameter	Value	Unit	Context
Electrode Material	Hole-Arrayed Boron-Doped Diamond (HABDD)	N/A	Custom MPCVD free-standing anode
Electrode Area	4 x 4	cm²	Anode size used in the reactor
Electrode Thickness	1	mm	Same as the depth of the micro holes
Micro Hole Diameter	~500	µm	Designed for 3D reaction zone expansion
Maximum Applied Current	0.5	A	High-power operation for O₃ generation
Stable O₃ Production Rate	~0.36	mg/min	Maintained over 25 h durability test
O₃ Concentration Range (Generated)	0.064 to 0.382	mg/L	Dependent on applied current (0.1 A to 0.5 A)
Diclofenac Removal Efficiency (Max)	85.56	%	Achieved in 1 h using TiO₂/O₃/UV system
Optimal Electrolyte Flow Rate	150	mL/min	Highest removal efficiency achieved
Initial Diclofenac Concentration (Tested)	10 to 100	mg/L	Highest efficiency at 10 mg/L
TiO₂ Nanotube Film Thickness	~10	µm	Vertically aligned on Ti mesh
UV Wavelength	254	nm	Incident UV lamp source
Most Favorable Adsorption Energy (E_a)	-4.3352	eV	Bridging configuration (b) on TiO₂ (101) surface

Key Methodologies

The following steps outline the fabrication of the custom diamond electrode and the operational parameters of the electrochemical-photocatalytic reactor.

HABDD Electrode Fabrication: The free-standing Boron-Doped Diamond (BDD) film was custom-made using a Microwave Plasma-Assisted Chemical Vapor Deposition (MPCVD, 2.45 GHz) device.
Precursor and Doping: Acetone and Hydrogen gas mixture served as the carbon source. Trimethyl borate (B(OCH₃)₃) was mixed into the carrier gas to achieve the necessary boron doping for high conductivity.
Substrate Preparation: A Ta plate (10 x 10 cm²) with arrayed holes was used as the deposition substrate. Both sides were exposed sequentially to the plasma to ensure uniform diamond growth.
Photocatalyst Synthesis: TiO₂ nanotubes were synthesized on a Ti mesh substrate (4 x 4 cm²) via electrochemical anodization for 20 hours, resulting in vertically aligned anatase TiO₂ nanotubes (60-100 nm internal diameter).
Reactor Setup: The electrochemical cell utilized the HABDD film as the anode and a Platinum mesh as the cathode, separated by a Nafion film solid-state electrolyte membrane.
AOP Operation: The system operated in a continuous flowing mode. Diclofenac-containing tap water was circulated while the HABDD generated O₃ directly into the water stream, simultaneously illuminated by a 254 nm UV lamp.

6CCVD Solutions & Capabilities

The successful implementation of this high-performance Advanced Oxidation Process (AOP) hinges entirely on the quality, custom geometry, and electrochemical stability of the Boron-Doped Diamond (BDD) electrode. 6CCVD is uniquely positioned to supply and scale the required diamond materials for replicating and advancing this research.

Research Requirement (Paper)	6CCVD Solution & Capability	Technical Advantage & Sales Proposition
High-Performance Anode Material	Heavy Boron-Doped Diamond (BDD) Substrates.	Our MPCVD BDD films provide the widest electrochemical window and highest corrosion resistance necessary for efficient, long-term O₃ generation and hydroxyl radical (OH·) production in aggressive aqueous media. We guarantee the stability demonstrated (25+ hours) for industrial applications.
Custom 3D Electrode Geometry (HABDD)	Custom Laser Patterning & Precision Cutting.	The paper required a complex 1 mm thick electrode with precise 500 µm diameter hole arrays. 6CCVD offers advanced laser machining services to create custom 3D structures and complex geometries on BDD wafers, maximizing the active surface area for enhanced mass transfer kinetics.
Large-Scale Production Potential	PCD/BDD Plates up to 125 mm.	While the paper used a 4 x 4 cm² electrode, 6CCVD can scale production to inch-size wafers (up to 125 mm Polycrystalline Diamond) and large-area BDD plates, facilitating pilot plant development and commercial scale-up of this promising water treatment technology.
Thick, Free-Standing Electrodes	BDD Substrates up to 10 mm Thickness.	We routinely grow self-standing BDD films up to 10 mm thick, ensuring the mechanical robustness and structural integrity required for high-flow, high-power electrochemical reactors, eliminating the need for fragile substrates.
Metalization for Integration	In-House Custom Metalization (Au, Pt, Ti, etc.).	Although the HABDD was used as a bare anode, 6CCVD offers internal metalization services (e.g., Ti/Pt/Au contacts) to ensure low-resistance electrical connections and seamless integration into complex reactor designs.
Surface Quality Requirement	Polishing Services (Ra < 5 nm for PCD).	For applications requiring specific surface finishes or low roughness for optimal film deposition (like the TiO₂ nanotubes), 6CCVD provides high-quality polishing services.

Engineering Support: 6CCVD’s in-house PhD team specializes in the material science of electrochemical diamond applications. We offer consultation on optimizing boron doping concentration and surface termination for similar Advanced Oxidation Process (AOP) projects, ensuring maximum radical generation efficiency and electrode lifetime.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. Global shipping (DDU default, DDP available) ensures rapid delivery of custom diamond solutions worldwide.

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

Original Source

DOI: https://doi.org/10.3390/catal13050877

References

2021 - TiO2 assisted photocatalysts for degradation of emerging organic pollutants in water and wastewater [Crossref]
2016 - Degradation of pharmaceuticals in wastewater using immobilized TiO2 photocatalysis under simulated solar irradiation [Crossref]
2014 - Photolysis and TiO2-catalysed degradation of diclofenac in surface and drinking water using circulating batch photoreactors [Crossref]
2010 - Diclofenac removal from water by ozone and photolytic TiO2 catalysed processes [Crossref]
2005 - Comparison of O3-BAC, UV/O3-BAC and TiO2/UV/O3-BAC processes for removing organic pollutants in secondary effluents [Crossref]
2022 - Degradation of chlorinated volatile organic compounds from contaminated ground water using a carrier-bound TiO2/UV/O3-system [Crossref]
2014 - Integration of ozone and solar TiO2-photocatalytic oxidation for the degradation of selected pharmaceutical compounds in water and wastewater [Crossref]
2009 - Oxidation of methanol and total reduced sulfur compounds with ozone over V2O5/TiO2 catalyst: Effect of humidity [Crossref]
2003 - A comparative study on decomposition of gaseous toluene by O3/UV, TiO2/UV and O3/TiO2/UV [Crossref]