A Nanograss Boron and Nitrogen Co-Doped Diamond Sensor Produced via High-Temperature Annealing for the Detection of Cadmium Ions

At a Glance

Metadata	Details
Publication Date	2023-11-15
Journal	Nanomaterials
Authors	Xiaoxi Yuan, Yaqi Liang, Mingchao Yang, Shaoheng Cheng, Nan Gao
Institutions	Jilin University, State Key Laboratory of Superhard Materials
Citations	2
Analysis	Full AI Review Included

Executive Summary

This research details the development and characterization of a Nanograss Boron and Nitrogen Co-Doped Diamond (NGBND) electrode, fabricated using a simple, mask-free high-temperature annealing process, for highly sensitive electrochemical detection of cadmium ions (Cd²⁺).

Novel Fabrication Route: A simple, cost-effective method was used, involving the growth of an NGBND/Non-Diamond Carbon (NDC) composite followed by high-temperature annealing (800 °C) to selectively remove the NDC phase, yielding the nanograss structure without complex etching or masking.
Superior Sensitivity: The NGBND sensor achieved an excellent low detection limit (LOD) of 0.28 µg L^-1 for Cd²⁺ via Differential Pulse Anodic Stripping Voltammetry (DPASV), significantly below the WHO maximum limit of 3 µg L^-1 for drinking water.
Enhanced Surface Area: Cyclic Voltammetry (CV) confirmed that the nanograss morphology increased the estimated active electrochemical area by 8.5 times compared to the initial composite film.
Mechanism of Action: The high sensitivity is attributed to the large specific surface area and the simulated tip-enhanced current density near the nanograss tips (size around a few nanometers), which facilitates localized concentration and precipitation of Cd²⁺.
Robustness and Stability: The nanostructured diamond is covalently bonded to the substrate, ensuring long-term stability and preventing material fall-off, thereby eliminating the secondary pollution risks associated with traditional nanodiamond particle modifications.
Performance Metrics: The sensor demonstrated a wide linear range (1 to 100 µg L^-1) and high reproducibility (Relative Standard Deviation of 3.1%).

Technical Specifications

Parameter	Value	Unit	Context
Detection Limit (LOD)	0.28	µg L^-1	Cd²⁺ detection via DPASV
Linear Range	1 to 100	µg L^-1	Cd²⁺ concentration
Reproducibility (RSD)	3.1	%	For 100 µg L^-1 Cd²⁺
Active Area Enhancement	8.5	times	NGBND vs. NGBND/NDC composite (from CV)
Annealing Temperature	800	°C	Removal of Non-Diamond Carbon (NDC)
Annealing Time	20	min	In air, quartz tube
NGBND Tip Size	Few	nanometers	SEM observation
Diamond Raman Peak	1332	cm^-1	Characteristic diamond peak
Electrical Conductivity (Simulated)	2 x 10⁴	S m^-1	Used in COMSOL simulation
XPS Carbon Content (C 1s)	92.42	%	NGBND film composition
XPS Boron Content (B 1s)	1.41	%	NGBND film composition
XPS Nitrogen Content (N 1s)	0.59	%	NGBND film composition
DPASV Deposition Potential	-1.0	V	Pre-deposition accumulation
DPASV Determination Time	270	s	Pre-deposition accumulation

Key Methodologies

The Nanograss Boron and Nitrogen Co-Doped Diamond (NGBND) electrode was fabricated using a two-step process involving Microwave Plasma Chemical Vapor Deposition (MPCVD) followed by high-temperature annealing.

Substrate Preparation: p-type Si substrates were mirror-polished and ultrasonicated for 60 min in an acetone solution containing nano-diamond powders (approx. 5 nm) to form nucleation sites.
Cleaning: Substrates were sequentially cleaned ultrasonically in acetone, ethanol, and purified water (10 min each), then dried with nitrogen gas.
MPCVD Growth (Composite Film): Diamond films were deposited using a 2.45 GHz MPCVD system to create the NGBND/NDC composite.
- Boron Source: Liquid trimethyl borate (B(OCH₃)₃) was carried by H₂ gas bubbling.
- Reaction Gases: Methane (CH₄) and Hydrogen (H₂) were used, along with Nitrogen (N₂) as the co-dopant.
- Flow Rate: CH₄/H₂/B/N₂ flow rate was set at 20/200/2/1 sccm.
- Duration: The growth was maintained for 6 hours.
Nanograss Formation (Annealing): The composite film was annealed in a quartz tube at 800 °C for 20 min in the air. This step selectively etched away the Non-Diamond Carbon (NDC) phase, leaving behind the high-quality, nanograss-structured NGBND film.
Electrochemical Characterization: A standard three-electrode system was employed, using the NGBND film (0.10 cm² geometric area) as the working electrode, a platinum wire as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode.
Detection: Differential Pulse Anodic Stripping Voltammetry (DPASV) was performed in a 0.1 M acetate buffer (pH 5.5) with a deposition potential of -1.0 V and a determination time of 270 s for trace Cd²⁺ detection.

Commercial Applications

The NGBND material and its simple fabrication method offer significant advantages for deployment in high-performance electrochemical systems, particularly where stability and sensitivity are paramount.

Environmental Water Quality Monitoring:
- High-sensitivity, real-time detection of trace heavy metal ions (Cd²⁺, Pb²⁺, Zn²⁺, Cu²⁺) in drinking water and industrial wastewater, ensuring compliance with strict regulatory standards (e.g., WHO limits).
- Development of portable, robust electrochemical sensors for in-field monitoring due to the material’s chemical inertness and stability.
Advanced Electrochemical Sensing Platforms:
- Creation of highly selective and reproducible sensors for complex matrices, targeting biomolecules, drugs, pesticides, and organic environmental hazards.
- Utilization of the wide electrochemical potential window and low background current characteristic of doped diamond for enhanced signal-to-noise ratios in electroanalysis.
Electrode Manufacturing and Materials Science:
- Scalable production of nanostructured diamond electrodes using the simple annealing method, bypassing expensive and complex top-down techniques like plasma etching or template use.
- Integration into microfluidic and lab-on-a-chip devices requiring high surface area, stable, and conductive electrode materials.
Biomedical Devices:
- Application in biosensors and implantable devices, leveraging the known biocompatibility and high corrosion resistance of doped diamond materials.

View Original Abstract

The high-performance determination of heavy metal ions (Cd2+) in water sources is significant for the protection of public health and safety. We have developed a novel sensor of nanograss boron and nitrogen co-doped diamond (NGBND) to detect Cd2+ using a simple method without any masks or reactive ion etching. The NGBND electrode is constructed based on the co-doped diamond growth mode and the removal of the non-diamond carbon (NDC) from the NGBND/NDC composite. Both the enlarged surface area and enhanced electrochemical performance of the NGBND film are achievable. Scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse anodic stripping voltammetry (DPASV) were used to characterize the NGBND electrodes. Furthermore, we used a finite element numerical method to research the current density near the tip of NGBND. The NGBND sensor exhibits significant advantages for detecting trace Cd2+ via DPASV. A broad linear range of 1 to 100 μg L−1 with a low detection limit of 0.28 μg L−1 was achieved. The successful application of this Cd2+ sensor indicates considerable promise for the sensitive detection of heavy metal ions.

Tech Support

Original Source

DOI: https://doi.org/10.3390/nano13222955

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