How Are Carbon Nanotubes Made? Manufacturing Methods & Industrial Production

Carbon nanotubes (CNTs) have made a name for themselves as the superstars of nanotechnology. You've probably heard by now of their record-breaking strength, high conductivity, and light weight. Now carbon nanotubes are breaking out of the lab and making their way into next-generation materials – in significant volume. But how are carbon nanotubes made? It's essential to understand the synthesis pathways to choose the right CNT type for your application. In this guide, we'll unpack the key methods used to manufacture carbon nanotubes and how these are scaled up to industrial production.

The Core Synthesis Methods: From Bench to Scale

Currently, the synthesis methods of carbon nanotubes include arc discharge, laser ablation, chemical vapor deposition, pyrolysis, hydrothermal and template methods. Among them, three primary methods dominate how carbon nanotubes are produced, each with distinct mechanisms, advantages, and limitations.

Method	Arc Discharge	Laser Ablation	Chemical Vapor Deposition (CVD)
Process	High current passed between graphite electrodes in inert gas (He, Ar). Anode carbon vaporizes, condenses on cooler cathode forming CNTs.	Intense pulsed laser vaporizes graphite target (with metal catalysts e.g., Ni, Co) in a high-temp inert gas furnace. Vapor condenses into CNTs.	Carbon-containing gas (e.g., CH₄, C₂H₄, C₂H₂, CO) decomposes on heated substrate coated with metal catalyst nanoparticles (Fe, Co, Ni, Mo) at 500-1200°C. Carbon atoms diffuse & assemble into CNTs.
Primary Output	Primarily MWCNTs; SWCNTs possible with metal catalysts.	High-purity, high-quality SWCNTs with narrow diameter distribution.	Highly versatile: SWCNTs & MWCNTs possible by tuning parameters (catalyst, temp, gas, flow).
Pros	Relatively simple setup. Produces high-quality, well-graphitized CNTs.	Excellent SWCNT quality. Good control over parameters.	High yield. Excellent scalability (lab to large continuous reactors). Good control over CNT type, diameter, length, alignment. Lower cost per gram at scale.
Cons	Low yield. High energy consumption. Significant by-products (requires extensive purification). Discontinuous process. Difficult to scale.	Extremely high energy consumption. Very expensive equipment. Low yield. Batch process. Difficult & costly to scale industrially.	CNTs may have more defects than arc-discharge. Requires careful catalyst design & regeneration management. Purification often needed.
Primary Usage Scale	R&D / Limited production for specific high-quality needs.	R&D / Niche production.	Dominant Industrial Method (e.g., Fluidized Bed, Rotary Kiln reactors).

SWCNTs vs. MWCNTs: Production Nuances

• Single-walled CNTs (SWCNTs): Require smaller, more uniform catalyst particles and precise control over reaction conditions (temperature, carbon source, pressure) in CVD to prevent multi-wall formation. Often involve more complex catalyst systems (bimetallic) and lower growth temperatures than MWCNTs. Laser ablation also excels at SWCNT production.
• Multi-walled CNTs (MWCNTs): Generally easier to produce in high volumes via CVD. Tolerate a wider range of catalyst sizes and reaction conditions. Arc discharge naturally favors MWCNT formation.

Functionalization: Tailoring CNT Properties

CNTs are frequently functionalized after synthesis to enhance their solubility, dispersibility, or to introduce covalent bonding sites for attachment within a composite matrix. Two common types supplied by Alfa Chemistry include:

• OH-functionalized CNTs: Hydroxyl (-OH) groups are present on the CNT surface. These can be added via oxidation followed by reduction or direct treatments.
• COOH-functionalized CNTs: Carboxyl (-COOH) groups are present on the CNT surface. This functionalization is often done via oxidation in a strong acid (or acid mixture) such as nitric/sulfuric acid. The COOH provides a negatively charged surface that greatly increases the dispersibility in water, and is a useful starting point for further chemical modification.

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