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Thirty years ago, scientists successfully carried out the first controlled synthesis of single-walled carbon nanotubes. Since then, these nanotubes have been incorporated into products ranging from textiles and sporting goods to batteries and solar cells. As their uses have grown, so too has interest regarding their potential applications.
Researchers are actively pursuing new and innovative applications for these materials because of their unique properties. Success could mean crucial advances in renewable energy, drug delivery, and more. The possibilities for carbon nanotubes are immense across many industries.
What are single-walled carbon nanotubes?
Single-walled carbon nanotubes can be thought of as a single sheet of carbon atoms, similar to graphene, that are rolled into a tube shape. They’re commonly generated in a vacuum furnace where a catalyst-containing substrate interacts with a gas precursor that contains carbon. That precursor reacts with the catalytic substrate, leading to the growth of nanotubes in a process similar to making films in semiconductor manufacturing.
The publication of a controlled reaction to make single-walled carbon nanotubes followed the discovery of multi-walled carbon nanotubes in 1991. Multi-walled nanotubes can have large variations in their mechanical and electrical properties, so scientists have often pursued the single-walled variety to have more control over their characteristics. The key innovation allowing the synthesis of single-walled nanotubes was the use of catalyst particles in the deposition process.
Carbon nanotubes feature strong bonds between carbon atoms. Their tensile strength can be higher than steel in addition to being lightweight, thermally conductive, and fillable with other materials or combined with other nano-scale materials to leverage their properties.
The electrical properties of single-walled carbon nanotubes are also interesting and highly structure-dependent. They can be fully conductive like a metal or semiconducting depending on their chirality, which is the degree of spiral twisting along their length. The chirality varies from tube to tube as they grow on a substrate and determines whether an individual nanotube is semiconducting or behaves like a metal.
Applications of single-walled carbon nanotubes to date
These unique properties like high strength and low weight make single-walled carbon nanotubes important additions to composite materials. They’re commonly used in protective body armor, sporting goods such as tennis rackets and bicycles, and durable goods like boats and yachts.
The electrical properties of carbon nanotubes have also opened up significant possibilities and are already used in mass-market electronics like lithium-ion batteries for EVs. A recent study demonstrated that carbon nanotubes improved the power capabilities and lifespan of electrodes in those types of batteries. Thanks to their strength, carbon nanotubes also help the electrode in the battery better withstand mechanical stresses associated with charging/discharging cycles and flexing.
Opportunities for innovation
Battery-based energy storage and renewable energy are just two of the many potential applications for single-walled carbon nanotubes. An analysis of the CAS Content Collection™ using natural language processing was recently published in ACS Nano and reveals several interesting trends and connections.
Some applications appear more frequently in patents compared to journal publications, notably batteries, imaging, and electromagnetic shielding. This suggests that these applications are considered to have more commercial potential. The growth in EV adoption and resulting demand for lithium-ion batteries in recent years corresponds to the significant number of single-walled carbon nanotube mentions in battery patent applications.
Other fields are seeing more activity in academic research. Photonics and solar cells, for example, are active areas of research, and hydrogen storage is a small but growing field of study. This is because the nanotubes’ large surface area allows them to efficiently adsorb hydrogen gas, which can overcome long-standing challenges in storing it. Adding nanoparticles to the surface of the nanotubes can drive more reactions with hydrogen to further increase the nanotubes’ ability to absorb it.
Biomedical applications such as drug delivery — while very different from the other use cases for single-walled carbon nanotubes — are also important to researchers since these molecules could play a role in personalized medicine. Implantable electrodes, which would leverage nanotubes’ enhanced conductivity, are another potential innovation in the biomedical field, as wearable and implantable neurotechnology devices are becoming a reality.
These applications are ripe for more research and demonstrations of safety, efficacy, and consistency, but they show that single-walled carbon nanotubes offer an immense range of scientific possibilities.
Large potential for nanotechnologies
In the past 30 years, single-walled carbon nanotubes have gone from the subject of fundamental lab studies to commercialized innovations across numerous industries. Now they are positioned to be critical in the energy transition, the evolution of EVs, and even personalized medicine.
Nanotubes, along with other emerging nanomaterials, will continue to reshape the future. From sustainable alternatives of biomaterials and new applications like 3D printing in biomedicine fields, this rapid pace of innovation will continue to accelerate in the years ahead.