Multi-walled Carbon Nanotubes: Manufacturing, Characterization and Applications

What is Multi-walled Carbon Nanotubes?

Multi-walled carbon nanotubes (MWCNTs) are cylindrical nanostructures composed of multiple concentric layers of graphene sheets. They have unique physical and chemical properties, including high electrical and thermal conductivity, mechanical strength, and a large surface area. MWCNTs are used in a variety of applications, such as electronics, energy storage, sensors, and composites.

Figure 1. Scheme of multi-walled carbon nanotube (MWCNT) synthesis

Product List

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Catalog Number	Product Name
ACM308068566-363	Multi-Wall Carbon Nanotube
ACM308068566-180	Carbon nanotube array, multi-walled, drawable
ACM308068566-324	Carbon Nanotube Array, Multi-walled (vertically aligned on Si substrate)
ACM308068566-325	Carbon Nanotube Array, Multi-walled (vertically aligned on Si substrate, H 0.5 mm)
ACM308068566-326	Carbon Nanotube Array, Multi-walled (vertically aligned on Si substrate, height 1.0 mm)
ACM308068566-328	Carbon Nanotube, Double-walled (≤10% Metal Oxide)
ACM308068566-329	Carbon Nanotube, Double-walled (50-80% Carbon Basis)
ACM308068566-330	Carbon Nanotube, Multi-walled (>90% Carbon basis)
ACM308068566-331	Carbon Nanotube, Multi-walled (<5% Metal Oxide)
ACM308068566-332	Carbon Nanotube, Multi-walled (>95% Carbon basis)
ACM308068566-333	Carbon Nanotube, Multi-walled (>98% Carbon basis)
ACM308068566-334	Carbon Nanotube, Multi-walled (As-produced cathode deposit)
ACM308068566-335	Carbon Nanotube, Multi-walled (Flake of bundled CNTs)
ACM308068566-336	Carbon Nanotube, Multi-walled (Powdered cylinder cores)
ACM308068566-337	Carbon Nanotube, Multi-walled (Thin and short, <5% Metal Oxide)

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Properties of Multi-walled Carbon Nanotubes

• High mechanical strength: Multi-walled carbon nanotubes (MWCNTs) have exceptional mechanical properties, with a tensile strength that is several times greater than steel.
• Electrical conductivity: MWCNTs exhibit excellent electrical conductivity, making them attractive for use in a wide range of electrical and electronic applications.
• Thermal conductivity: MWCNTs have high thermal conductivity, making them suitable for use in thermal management applications such as heat sinks.
• Chemical stability: MWCNTs are chemically stable and resistant to corrosion, which makes them ideal for use in harsh environments.
• High aspect ratio: MWCNTs have a high aspect ratio, with lengths that can be thousands of times their diameter. This high aspect ratio gives them unique properties and makes them suitable for use in a variety of applications.
• Lightweight: MWCNTs are lightweight and have a low density, making them ideal for use in aerospace and automotive applications where weight reduction is important.
• High surface area: MWCNTs have a high surface area, which makes them suitable for use in energy storage applications such as supercapacitors and lithium-ion batteries.
• Biocompatibility: MWCNTs have been shown to be biocompatible and are being investigated for use in biomedical applications such as drug delivery, tissue engineering, and biosensing.

Synthesis of Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWCNTs) can be synthesized using various methods, with the most common being chemical vapor deposition (CVD) and arc discharge. Here is a general overview of the synthesis process using CVD:

• Catalyst preparation: A catalyst, typically iron, nickel, or cobalt nanoparticles, is dispersed on a substrate, such as silicon wafer, quartz, or alumina, using methods like spin-coating, dip-coating, or sputtering.
• Reactor setup: The catalyst-coated substrate is placed inside a CVD reactor, which is then evacuated and purged with an inert gas, such as argon, to create a controlled environment.
• Carbon source introduction: A carbon-containing precursor gas, such as ethylene, acetylene, or methane, is introduced into the reactor along with a carrier gas, typically hydrogen or argon.
• Heating: The reactor is heated to a high temperature (typically 600-900°C) to facilitate the decomposition of the carbon precursor gas and the subsequent growth of carbon nanotubes on the catalyst nanoparticles.
• Carbon nanotube growth: As the carbon precursor gas decomposes, carbon atoms adsorb on the surface of the catalyst nanoparticles and form carbon nanotubes through a vapor-solid-solid mechanism. The catalyst nanoparticles act as a template for the growth of the carbon nanotubes, with multiple layers stacking up to form multi-walled structures.
• Cooling and collection: After the desired growth time, the reactor is cooled down, and the MWCNTs are collected from the catalyst-coated substrate using methods like sonication in a solvent or mechanical abrasion.
• Purification and characterization: The collected MWCNTs are typically purified to remove any residual catalyst particles and other impurities. The MWCNTs can then be characterized using techniques like scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction to determine their quality, structure, and properties.

Overall, the synthesis of MWCNTs using CVD is a versatile and efficient method for producing high-quality carbon nanotubes. This method allows for control over the length, diameter, and alignment of the nanotubes, making it suitable for a wide range of applications in various fields such as electronics, materials science, and medicine.

Applications of Multi-walled Carbon Nanotubes

• Energy storage: Multi-walled carbon nanotubes have shown promise in improving the performance and capacity of batteries and supercapacitors due to their high surface area and conductivity.
• Composite materials: Multi-walled carbon nanotubes can be used as additives in composites to enhance their mechanical, thermal, and electrical properties. They are commonly used in applications such as aerospace, automotive, and sporting goods.
• Sensors: Multi-walled carbon nanotubes have been used to develop highly sensitive sensors for detecting gases, biomolecules, and other substances. Their high surface area and conductivity make them ideal for sensing applications.
• Biomedical applications: Multi-walled carbon nanotubes have shown potential in various biomedical applications, including drug delivery, tissue engineering, and medical imaging. They can be functionalized with targeting ligands or therapeutic agents to enhance their biomedical properties.
• Environmental remediation: Multi-walled carbon nanotubes can be used in environmental remediation processes to remove pollutants from water and air. They have been shown to effectively adsorb contaminants such as heavy metals and organic pollutants.
• Catalysis: Multi-walled carbon nanotubes have been used as catalyst supports in various chemical reactions due to their high surface area and stability. They have shown promise in applications such as fuel cells, hydrogen production, and environmental catalysis.

Reference

1. Kumanek, B., et al. Impact of synthesis parameters of multi-walled carbon nanotubes on their thermoelectric properties. Materials. 2019, 12(21), 3567.