Electrochemical Properties and Chemical Oxygen Demand Depending on the Thickness of Boron-Doped Diamond

At a Glance

Metadata	Details
Publication Date	2020-11-16
Journal	Coatings
Authors	Chang Song, Mi Young You, Jae‐Myung Lee, Dae‐Seung Cho, Pung Keun Song
Institutions	Pusan National University
Citations	3
Analysis	Full AI Review Included

Executive Summary

This research focuses on developing a cost-effective, high-performance Boron-Doped Diamond (BDD) electrode via Hot-Filament Chemical Vapor Deposition (HFCVD) for advanced wastewater treatment.

Cost Reduction Strategy: Manufacturing costs were lowered by substituting expensive gas precursors with liquid solutions (acetone and trimethyl borate, TMB) and using reusable tantalum filaments instead of single-use tungsten.
Consistent Deposition: The BDD film exhibited a constant deposition rate of 100 nm/h, allowing predictable thickness control (e.g., 5.6 µm thickness achieved after 60 hours).
High Doping Level: Boron doping was successfully achieved at a calculated concentration of 11,400 ppm, confirmed by the characteristic shift and broadening of the Raman peak (1210 cm^-1).
Superior Performance: The BDD anode demonstrated exceptional efficiency in degrading nonbiodegradable organic contaminants, achieving an average Chemical Oxygen Demand (COD) removal rate of 90-92%.
Competitive Advantage: This BDD performance is significantly higher than the 47.35% COD removal rate observed using the currently widespread IrO₂ reference electrode.
Electrochemical Stability: Electrochemical activation and catalytic activity were found to be independent of film thickness, confirming that the surface properties—which drive the oxidation process—are consistent across different deposition times.

Technical Specifications

Parameter	Value	Unit	Context
Deposition Method	HFCVD	N/A	Hot-Filament Chemical Vapor Deposition
Filament Material	Tantalum (Ta)	N/A	Used for reusability and cost reduction
Filament Input Power	16	kW	Optimized power setting
Working Pressure	4000	Pa	Pressure during deposition
Filament-Susceptor Distance	10	mm	Optimized working distance
Carbon Source Flow Rate	90	sccm	Acetone vapor supplied via bubbling
Boron Source Flow Rate	6	sccm	TMB vapor supplied via bubbling
Deposition Rate	100	nm/h	Constant rate observed
Boron Doping Level	11,400	ppm	Calculated concentration
Film Thickness (12h)	1.1 ± 0.2	µm	Cross-sectional FE-SEM measurement
Film Thickness (60h)	5.6 ± 0.5	µm	Cross-sectional FE-SEM measurement
Electrolysis Voltage	5	V	Used for COD degradation tests
Initial COD Concentration	6500	ppm	Farm wastewater sample
BDD COD Removal (60h film)	92	%	Achieved after 2 hours of electrolysis
IrO₂ COD Removal (Reference)	47.35	%	Achieved after 2 hours of electrolysis
Boron-Induced Raman Shift	1210	cm^-1	Broad peak confirming heavy doping
Potential Window (CV)	~2.5	V	Range between inflection points

Key Methodologies

The BDD films were deposited using a modified HFCVD process optimized for cost efficiency and performance.

Substrate Preparation: Silicon (for thickness measurement) and Niobium (for electrochemical tests) substrates were pretreated. This involved ultrasonic cleaning, followed by seeding using a 500 nm diamond powder/glycerin mixture (1:1 weight ratio) rubbed onto the surface to enhance nucleation.
HFCVD Setup: Twelve rows of Tantalum filaments were installed. The susceptor holding the substrate was rotated at 1 rpm to ensure uniform temperature distribution and film deposition.
Precursor Management: Acetone (carbon source) and Trimethyl Borate (TMB, boron source) solutions were used as liquid precursors. Hydrogen gas acted as the carrier gas for the bubbling system.
Vapor Pressure Control: To maintain a consistent supply of precursors, the acetone and TMB bubblers were immersed in an antifreeze solution held precisely at 0 °C using a thermostat.
Deposition Recipe: Films were grown under 16 kW input power, 4000 Pa pressure, and a 10 mm filament-susceptor distance. Deposition times were varied (12 h and 60 h) to study thickness effects.
Material Characterization:
- Morphology and thickness were verified using Field Emission Scanning Electron Microscopy (FE-SEM).
- Crystallinity and substrate carbonization were analyzed via X-ray Diffraction (XRD).
- Boron doping and diamond quality were confirmed using Raman spectroscopy (argon laser, 514.5 nm excitation).
Electrochemical Evaluation: Cyclic Voltammetry (CV) was performed in 0.5 M Na₂SO₄ solution to determine the potential window and in a K₃Fe(CN)₆/K₄Fe(CN)₆ mixture to assess catalytic activity.
Wastewater Testing: COD degradation tests were run on real farm wastewater (6500 ppm initial COD) using a constant voltage of 5 V, comparing BDD performance against a commercial IrO₂ electrode.

Commercial Applications

The development of cost-effective, high-performance BDD electrodes opens significant opportunities, particularly in environmental engineering and advanced oxidation processes.

Advanced Wastewater Treatment (AWT):
- Electrochemical oxidation of highly stable, nonbiodegradable organic pollutants (e.g., pharmaceuticals, pesticides, dyes) where conventional biological methods fail.
- The high efficiency (92% COD removal) makes BDD ideal for tertiary treatment stages.
Water Disinfection and Reuse:
- Generating powerful oxidizing agents (hydroxyl radicals, ozone) for effective disinfection and removal of pathogens and trace organic contaminants, enabling safe water recycling.
Electrochemical Synthesis:
- Use in industrial processes requiring strong, stable anodes for the synthesis of specialty chemicals or electrochemical conversion reactions.
Cost-Competitive Electrode Manufacturing:
- The successful substitution of expensive gas precursors with liquid solutions and the use of reusable tantalum filaments drastically lowers the barrier to entry for BDD electrode production, making BDD a viable replacement for IrO₂ in large-scale industrial applications.

View Original Abstract

In this study, boron-doped diamond (BDD) film was deposited by hot-filament chemical vapor deposition (HFCVD) using acetone as the carbon source and trimethyl borate (TMB) as the boron source with the aim of lowering the manufacturing cost of BDD electrodes. The BDD film was deposited for 12 and 60 h to observe changes in the morphological behavior of the film as well as subsequent changes in the electrochemical properties. The morphology of the BDD film was not affected by the deposition time, but the thickness increased with increasing deposition time. As the deposition time increased, the deposition rate of the BDD film did not increase or decrease; rather, it remained constant at 100 nm/h. As the thickness of the BDD film increased, an increase in the potential window was observed. On the other hand, no distinct change was observed in the electrochemical activation and catalytic activity depending on the thickness, and there were not many differences. Chemical oxygen demand (COD) was measured to determine the practical applicability of the deposited BDD film. Unlike the potential window, the COD removal rate was almost the same and was not affected by the increase in the thickness of the BDD film. Both films under the two deposition conditions showed a high removal rate of 90% on average. This study confirms that BDD electrodes are much more useful for water treatment than the existing electrodes.

Tech Support

Original Source

DOI: https://doi.org/10.3390/coatings10111097

References

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