First discovered under an electron microscope over a half a century ago, carbon nanotubes are one of the most sought-after materials today. The tiny structures are used in dozens of applications that touch nearly every industry, including aerospace, electronics, medicine, defense, automotive, energy, construction, and even fashion.
Carbon nanotubes (aka CNTs) are made from graphene sheets consisting of a single atomic layer of carbon atoms in a honeycomb framework that can be rolled into a tube measuring about a nanometer, or one billionth of a meter, in diameter.
At this scale, these cylindrical molecules defy the classic laws of physics with exceptional properties. Carbon nanotubes have excellent electrical conductivity, the ability to withstand high working temperatures, and the highest strength-to-weight ratio of any known material.
Scientists are developing new applications using these nanomaterials at a staggering clip. Below are five notable research areas that demonstrate the sweeping impact of CNTs:
Carbon nanotube "cupcakes" may help measure terahertz laser light
Unlike the tasty cupcakes your grandmother makes, these are made up of vertically aligned carbon nanotube arrays (VANTAs) that are grown on silicon (which appears blue in the image). Using a razor blade, visible chunks of these densely packed arrays can be sliced off and placed on top of a laser power detector to detect terahertz radiation. Terahertz radiation can penetrate materials like plastic, clothing, paper and some biological tissues, making it an attractive candidate for applications such as concealed weapons detection, package inspection and imaging skin tumors. Until now, there wasn't a standard method for measuring the output power of terahertz lasers, but researchers at the National Institute of Standards and Technology (NIST) think they have a winner with these nano-cakes. Learn more.
Carbon nanotubes for cleaning polluted water
Credit: Department of Environmental Geosciences, University of Vienna
Scientists found that by using filters made of carbon nanotubes, pollutants could be removed more effectively from contaminated water as compared to common charcoal filters. CNTs have a very large surface area (e.g., 500 m2 per gram of nanotube) that gives them a high capacity to retain pollutants such as water soluble drugs. A team at the University of Vienna found that at concentrations likely to occur in the environment, the tubes removed 13 tested Polycyclic Aromatic Hydrocarbons (PAHs) from contaminated water. The results were recently published in the journal Environmental Science and Technology. However, there are still many health and environmental questions to answer before such filters find their way into municipal water treatment plants. Learn more.
Boosting solar energy storage by a factor of 10,000
The business of storing solar energy in molecules that change state in response to light could be entirely transformed by carbon nanotubes. Researchers at the Massachusetts Institute of technology (MIT) have announced a new solar thermal fuel that could store up to 10,000 times more energy than previous systems. The fuel consists of carbon nanotubes modified with azobenzene, a mix that is expected to provide the same energy storage per volume as lithium-ion batteries and can store solar energy almost indefinitely. It can also be recharged by simply exposing it to sunlight – no electricity required. There are some catches, however. The fuel has been studied using computational chemistry but not yet fully tested in the lab, so commercialization is still far off. Another limitation is that to produce electricity would require another conversion step, using thermoelectric devices or producing steam to run a generator. Learn more.
Tubes by the ton for more efficient electrical transmission lines
Credit: Barron Lab/Rice University
Pure metallic carbon nanotubes could be the key to overhauling the electrical power grid with more efficient transmission lines -- but only if they could be made in huge quantities and uniformly. Through a refined version of a technique called "amplification," researchers at Rice University plan to make long and highly conductive nanotube fibers they dubbed "armchair quantum wire" that could be woven into more efficient electrical transmission lines. They eagerly plan to generate a large quantity of this material by the end of summer. Aaron Franklin, a researcher at IBM's Watson Research Center says that the update Rice study probably doesn't reveal "the golden ticket for achieving high volumes of metallic-only tubes," reports MIT Technology Review. We'll just have to wait and see. Learn more.
Molecular syringes, probes, and bioelectronic noses
Credit: Robert R. Johnson, University of Pennsylvania
Medical researchers are eying carbon nanotubes as well, such as potential needles for injecting drugs or genes into sick cells. Size and shape are only half the reason why. As probes, their physical properties, including their great electrical and thermal conductivity, make them particularly suited for exchanging information between the inside and outside of the cell. Nanotube probes may be used to test for certain substances and test certain processes beyond cell membranes. But that's just the beginning. A group of researchers is developing a carbon nanotube transistor that can "smell" by integrating a CNT transistor with olfactory receptor proteins taken from mice. The goal of this type of research, Nanowerk reports, is to transfer the sensing properties of biological molecular systems to artificial electronic devices. Learn more.
Carbon nanotubes and the broader field of nanotechnology have the potential to transform our lives, but it could be decades before that potential is fully developed.