High-Density and Monodisperse Electrochemical Gold Nanoparticle Synthesis Utilizing the Properties of Boron-Doped Diamond Electrodes

At a Glance

Metadata	Details
Publication Date	2022-05-19
Journal	Nanomaterials
Authors	Kenshin Takemura, Wataru Iwasaki, Nobutomo Morita, Shinya Ohmagari
Institutions	National Institute of Advanced Industrial Science and Technology
Citations	12
Analysis	Full AI Review Included

Executive Summary

This research details a rapid, high-density electrochemical synthesis method for Gold Nanoparticles (AuNPs) on Boron-Doped Diamond (BDD) electrodes, resulting in a highly sensitive sensor for Arsenic (As(III)) detection.

Core Achievement: Successful fabrication of AuNP-modified BDD (AuNP-BDD) electrodes featuring high density (132 ± 7 particles/µm²) and monodispersity (56 ± 5 nm) of AuNPs.
Synthesis Advantage: The wide potential window of the BDD electrode enabled the use of a high negative voltage (-1.8 V) for rapid, uniform electrochemical AuNP deposition in a short duration (30-60 s).
Performance Metric: The optimized AuNP-BDD electrode achieved a Limit of Detection (LoD) for As(III) of 0.473 ppb using Square-Wave Anodic Stripping Voltammetry (SWASV).
Sensitivity: This LoD is significantly lower than the World Health Organization (WHO) standard for arsenic in drinking water (10 ppb).
Detection Speed: The system allows for rapid As(III) detection, completing the analysis within 10 minutes of contact with the analyte solution.
Robustness: The BDD substrate provides low background current and excellent chemical stability, crucial for reliable heavy metal stripping analysis.

Technical Specifications

Parameter	Value	Unit	Context
AuNP Synthesis Voltage (Optimal)	-1.8	V	Electrochemical deposition time: 60 s
AuNP Synthesis Time (Optimal)	60	s	Electrochemical deposition at -1.8 V
AuNP Average Size	56 ± 5	nm	Optimal 60 s deposition
AuNP Density	132 ± 7	particles/µm²	Optimal 60 s deposition
As(III) Limit of Detection (LoD)	0.473	ppb	Using AuNP-BDD electrode (SWASV)
As(III) Linear Detection Range	2-150	ppb	SWASV measurement
BDD Film Thickness	5	µm	Typical fabrication result
BDD Boron Concentration	greater than 10²⁰	cm^-3	Heavily boron-doped polycrystalline film
CVD Chamber Pressure	1.3	kPa	BDD fabrication (Hot-filament CVD)
Methane/Hydrogen Ratio	3	%	BDD fabrication
Filament Temperature	2200	°C	BDD fabrication (Hot-filament CVD)
As(III) Electrodeposition Voltage (E_dep)	-0.7	V	Optimal voltage for arsenic stripping
As(III) Electrodeposition Time	300	s	SWASV stirring period
SWASV Scan Rate	12	mV	Measurement sweep rate
SWASV Frequency	45.0	Hz	Measurement frequency
AuNP Crystal Plane Peaks (XRD)	38.2°, 44.3°, 64.4°, 78.2°	2θ, degrees	Corresponds to (111), (200), (220), (221) planes

Key Methodologies

The fabrication of the high-performance AuNP-BDD electrode involved two primary steps: BDD film growth and optimized electrochemical AuNP deposition.

1. BDD Electrode Fabrication (Hot-Filament CVD)

Substrate Preparation: Si(100) substrates were pre-seeded using commercial diamond nanopowder (4-6 nm size) to facilitate diamond nucleation.
Gas Composition: Hydrogen, methane (CH₄), and trimethylboron were fed into the CVD chamber. The CH₄/H₂ ratio was maintained at 3%.
Process Conditions: Total pressure was maintained at 1.3 kPa. Tungsten filaments were heated resistively to 2200 °C.
Resulting Film: Heavily boron-doped polycrystalline diamond film with a thickness of 5 µm and a boron concentration exceeding 10²⁰ cm^-3.

2. AuNP Coating (Short-Time Pulse-Inducing Method)

Electrolyte: 0.4% Potassium tetrachloroaurate (III) (KAuCl₄) solution.
Setup: Standard three-electrode system (BDD working electrode, Pt counter electrode, Ag/AgCl reference electrode).
Optimization: The BDD’s wide potential window was exploited to apply a high negative voltage without immediate water electrolysis interference.
Optimal Deposition Parameters: A voltage of -1.8 V was applied for 60 s using chronoamperometry without stirring.
Post-Treatment: The AuNP-BDD electrode was rinsed with ultrapure water.

3. As(III) Electrochemical Detection (SWASV)

Electrolyte: 0.1 M acetic acid buffer (AcONa) at pH 5.
Electrodeposition (Stripping): As(III) ions were electrodeposited as As(0) onto the AuNPs under an applied voltage (E_dep) of -0.7 V while stirring for 300 s.
Static Period: Stirring was stopped, and the potential was held at -0.7 V for 15 s.
Measurement: The voltage was swept from -0.3 V to 0.3 V (Scan Rate: 12 mV, Amplitude: 25.0 mV, Frequency: 45.0 Hz).

Commercial Applications

The robust, sensitive, and rapid detection capabilities of the AuNP-BDD electrode make this technology highly relevant for several engineering and industrial sectors:

Environmental Monitoring and Water Quality:
- Onsite, rapid detection of toxic heavy metals (specifically As(III)) in groundwater, rivers, and drinking water sources, enabling immediate regulatory action.
- Deployment in remote or resource-limited areas where complex laboratory equipment is impractical.
Industrial Wastewater Treatment:
- Real-time monitoring of heavy metal concentrations in industrial effluent streams to ensure compliance with discharge limits.
Agricultural and Soil Analysis:
- Convenient monitoring of arsenic contamination in agricultural soils and irrigation water, critical for food safety and public health maintenance.
Chemical Sensor Manufacturing:
- Fabrication of next-generation electrochemical sensors utilizing BDD substrates for enhanced stability, sensitivity, and reduced background noise in various analytical applications.
Portable Analytical Devices:
- Integration into handheld or portable voltammetry devices for field testing due to the short fabrication time (60 s) and rapid analysis time (less than 10 minutes).

View Original Abstract

Owing to its simplicity and sensitivity, electrochemical analysis is of high significance in the detection of pollutants and highly toxic substances in the environment. In electrochemical analysis, the sensitivity of the sensor and reliability of the obtained signal are especially dependent on the electrode characteristics. Electrodes with a high density of nanomaterials, which exhibit excellent activity, are useful as sensor substrates for pollutant detection. However, the effective placement of high-density nanomaterials requires a high degree of control over the particle size, particle shape, and distance between the particles on the substrate. In this study, we exploited the properties of boron-doped diamond (BDD) electrodes, which have a wide potential window, and succeeded in coating a highly dense layer of gold nanoparticles (AuNPs) at high potential. The AuNP-modified BDD (AuNP-BDD) electrodes comprising less than 100 nm AuNPs at a density of 125 particles/µm were electrochemically synthesized over a short period of 30-60 s. The AuNP-BDD electrodes were applied for detecting arsenic, which is one of the most abundant elements, and exhibited a limit of detection of 0.473 ppb in solution.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano12101741

References

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