Enhanced electrochemical oxidation of phenol by boron-doped diamond nanowire electrode

At a Glance

Metadata	Details
Publication Date	2017-01-01
Journal	RSC Advances
Authors	Choong-Hyun Lee, Eung-Seok Lee, Young-Kyun Lim, Kang-Hee Park, Hee‐Deung Park
Institutions	Seoul Institute, Korea University
Citations	61
Analysis	Full AI Review Included

Technical Documentation & Analysis: Nanostructured BDD Electrodes for Advanced Oxidation Processes

Executive Summary

This documentation analyzes the fabrication and performance of Boron-Doped Diamond Nanowire (BDDNW) electrodes via Metal-Assisted Chemical Etching (MACE) and Hot-Filament Chemical Vapor Deposition (HFCVD) for enhanced electrochemical phenol oxidation. The key findings and value propositions are:

3x Enhanced Effective Surface Area: Nanostructuring the BDD surface increased the calculated electrochemical effective surface area by nearly three times (4.78 cm²) compared to conventional planar BDD (1.61 cm²).
Superior Organic Removal Efficiency: BDDNW electrodes achieved 98.9% Chemical Oxygen Demand (COD) removal and 96.9% Total Organic Carbon (TOC) removal, significantly outperforming planar BDD (94.4% COD, 79% TOC removal).
Mass Transfer Improvement: The nanowire structure facilitates greater generation of hydroxyl radicals (^•OH) and improves mass transfer kinetics, evidenced by a significantly reduced peak-to-peak potential separation (ΔE_p = 0.22 V vs. 0.62 V for planar BDD).
Dramatically Reduced Energy Consumption: For 80% mineralization of phenol, BDDNW reduced the required specific energy consumption by over 50%, requiring only 12.1 kWh m^-3 compared to 27.5 kWh m^-3 for planar BDD.
High Commercial Relevance: This nanostructuring approach addresses the primary limitation of high BDD production cost per unit area, demonstrating a pathway for high-productivity BDD anodes suitable for industrial wastewater treatment applications.

Technical Specifications

Parameter	Value	Unit	Context
Material	Boron-Doped Diamond Nanowire (BDDNW)	N/A	Anode material for AOPs
Dopant Concentration	5000	ppm	[B]/[C] ratio in feed gas (B₂H₆ diluted in H₂)
Substrate Type	p-type Si (100)	N/A	Resistivity: 0.005 Ω cm
CVD Temperature	800	°C	HFCVD deposition temperature
CVD Pressure	< 10	kPa	Total chamber pressure
BDDNW Length	750	nm	Average length of nanowire structure
BDDNW Thickness	200	nm	Average thickness of BDD layer on nanowires
BDDNW Effective Area	4.78	cm²	Calculated electrochemical effective area (CV method)
Planar BDD Effective Area	1.61	cm²	Calculated electrochemical effective area (CV method)
Current Density Applied	30	mA cm^-2	Galvanostatic electrolysis mode
Electrolyte	0.5 M Na₂SO₄	N/A	Electrolysis solution
Phenol Initial Conc.	1.0	mM	Target organic compound concentration
COD Removal (BDDNW)	98.9	%	Achieved at 2.5 Ah L^-1
TOC Removal (BDDNW)	96.9	%	Total Organic Carbon removal rate
Energy Consumption (80% Min.)	12.1	kWh m^-3	Specific energy required for 80% mineralization (BDDNW)

Key Methodologies

The BDDNW electrodes were fabricated using a multi-step process combining chemical surface etching, nanodiamond seeding, and chemical vapor deposition:

Substrate Preparation:
- Substrate: p-type Si (100) wafer (0.005 Ω cm resistivity).
- Cleaning: Ultrasonic cleaning in ethanol/deionized water, followed by immersion in 1% HF solution (30 min).
- Hydrophilicity Enhancement: Immersed in Piranha solution for 1 h.
Si Nanotexturing (MACE):
- Process: Metal-Assisted Chemical Etching (MACE).
- Etching Solution: 4.5 M HF and 0.01 M AgNO₃.
- Conditions: 5 min at 50 °C.
- Post-Etch Cleaning: Dipped in 30% HNO₃ to remove residual silver dendrites.
Nanodiamond Seeding (ESAND):
- Purpose: Provide dense nucleation sites.
- Surface Coating: Substrate coated with poly(diallyldimethylammonium chloride) (PDDA) for positive charge.
- Assembly: Negatively charged nanodiamond particles (in PSS and nanodiamond conjugate solution) were electrostatically attached (ESAND technique).
BDD Growth (HFCVD):
- CVD Method: Hot-Filament Chemical Vapor Deposition (HFCVD).
- Growth Time: 4 h.
- Substrate Temperature: 800 °C.
- Gas Composition: 1 vol% CH₄ in H₂.
- Flow Rate: 100 sccm (total flow).
- Boron Doping: B₂H₆ diluted gas maintaining a [B]/[C] ratio of 5000 ppm.
- Pressure: Maintained at less than 10 kPa.

6CCVD Solutions & Capabilities

6CCVD provides the foundational high-purity, heavily doped diamond materials required to replicate and scale this critical nanostructuring technology for advanced wastewater treatment and high-performance electrochemistry.

Applicable Materials

To achieve the superior electro-oxidation performance demonstrated by the BDDNW, the material must meet stringent criteria regarding doping concentration, purity, and substrate compatibility.

Heavy Boron-Doped Polycrystalline Diamond (PCD/BDD): The core material required is BDD grown via MPCVD, which offers superior crystallinity control compared to HFCVD, enabling higher sp³ content critical for oxidation power.
- Recommendation: 6CCVD’s Heavy Boron Doped PCD wafers are specified for electrochemical applications. We can precisely control the boron concentration up to the high levels (5000 ppm source ratio) needed to achieve the required conductivity and active site density, ensuring high Overpotential for the Oxygen Evolution Reaction (OER).
High-Purity Silicon Substrates: The research relies on a specific p-type Si (100) substrate with low resistivity (0.005 Ω cm).
- Recommendation: 6CCVD routinely handles custom-specified Si substrates, allowing direct deposition onto wafers matching the mechanical and electrical specifications necessary for effective MACE/ESAND pretreatment.

Customization Potential

Replicating this research demands specific dimensions and the integration of nanostructuring steps not typically offered by conventional CVD suppliers. 6CCVD’s advanced engineering services directly support these requirements:

Research Requirement	6CCVD Custom Capability	Benefit to Client
Substrate Compatibility	Custom Si substrate handling and pre-treatment consultation.	Ensures compatibility with MACE and ESAND seeding processes prior to BDD deposition.
BDD Thickness Control	SCD/PCD thickness range 0.1 µm - 500 µm.	Allows precise control over the deposited BDD layer thickness (e.g., 200 nm used in this study) for optimal nanowire structure integrity and cost efficiency.
Custom Wafer Size	Plates/wafers up to 125 mm (PCD).	Enables rapid scaling of experimental data from laboratory-scale (4 cm x 4 cm electrodes) to industrially relevant dimensions.
Metalization Layers	In-house capability for Au, Pt, Ti, W, Cu.	Essential for creating robust ohmic contacts and interconnects for use in full electrolytic circulation cells, ensuring long-term stability and minimal ohmic losses.

Engineering Support

This study highlights that achieving high performance in electrochemical applications depends not just on the bulk diamond quality, but on the resultant surface morphology and effective surface area.

6CCVD’s in-house PhD engineering team specializes in the material science of CVD diamond. We can assist clients in material selection and parameter definition for similar electrochemical wastewater treatment projects requiring maximal hydroxyl radical generation efficiency and minimized energy consumption. Our support ensures the diamond film properties (e.g., doping, sp³/sp² ratio, crystallinity) are optimized to integrate seamlessly with demanding post-processing techniques like MACE and ESAND.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

We fabricated a boron-doped diamond nanowire (BDDNW) electrode<italic>via</italic>metal-assisted chemical etching (MACE) of Si and electrostatic self-assembly of nanodiamond (ESAND) seeding to provide a large surface area during the phenol oxidation.

Tech Support

Original Source

DOI: https://doi.org/10.1039/c6ra26287b