Carbon Nanotubes Could Revolutionize Everything from Batteries and Water Purifiers to Auto Parts and Sporting Goods: Update from Lawrence Livermore National Laboratory

Vertically aligned carbon nanotubes growing from catalytic nanoparticles (gold color) on a silicon wafer on top of a heating stage (red glow). Diffusion of acetylene (black molecules) through the gas phase to the catalytic sites determines the growth rate in a cold-wall showerhead reactor. Credit: Image by Adam Samuel Connell/LLNL

Scientists at the Department of Energy’s Lawrence Livermore National Laboratory (LLNL)  are scaling up the production of vertically aligned single-walled carbon nanotubes (SWCNT). This incredible material could revolutionize diverse commercial products ranging from rechargeable batteries, sporting goods, and automotive parts to boat hulls and water filters. The research was published recently in the journal Carbon.

Most carbon nanotube (CNT) production today is unorganized CNT architectures that is used in bulk composite materials and thin films. However, for many uses, organized CNT architectures, like vertically aligned forests, provide critical advantages for exploiting the properties of individual CNTs in macroscopic systems.

“Robust synthesis of vertically-aligned carbon nanotubes at large scale is required to accelerate deployment of numerous cutting-edge devices to emerging commercial applications,” said LLNL scientist and lead author Francesco Fornasiero. “To address this need, we demonstrated that the structural characteristics of single-walled CNTs produced at wafer scale in a growth regime dominated by bulk diffusion of the gaseous carbon precursor are remarkably invariant over a broad range of process conditions.”

The team of researchers discovered that the vertically oriented SWCNTs retained very high quality when increasing precursor concentration (the initial carbon) up to 30-fold, the catalyst substrate area from 1 cm² to 180 cm², growth pressure from 20 to 790 Mbar and gas flowrates up to 8-fold.

LLNL scientists derived a kinetics model that shows the growth kinetics can be accelerated by using a lighter bath gas to aid precursor diffusion. In addition, byproduct formation, which becomes progressively more important at higher growth pressure, could be greatly mitigated by using a hydrogen-free growth environment. The model also indicates that production throughput could be increased by 6-fold with carbon conversion efficiency of higher than 90% with the appropriate choice of the CNT growth recipe and fluid dynamics conditions.

“These model projections, along with the remarkably conserved structure of the CNT forests over a wide range of synthesis conditions, suggest that a bulk-diffusion-limited growth regime may facilitate preservation of vertically aligned CNT-based device performance during scale up,” said LLNL scientist and first author Sei Jin Park.

The team concluded that operating in a growth regime that is quantitatively described by a simple CNT growth kinetics model can facilitate process optimization and lead to a more rapid deployment of cutting-edge vertically-aligned CNT applications.

Applications include lithium-ion batteries, supercapacitors, water purification, thermal interfaces, breathable fabrics, and sensors.

Reference: “Synthesis of wafer-scale SWCNT forests with remarkably invariant structural properties in a bulk-diffusion-controlled kinetic regime” by Sei Jin Park, Kathleen Moyer-Vanderburgh, Steven F. Buchsbaum, Eric R. Meshot, Melinda L. Jue, Kuang Jen Wu and Francesco Fornasiero, 29 September 2022, Carbon.
DOI: 10.1016/j.carbon.2022.09.068

Other LLNL authors are Kathleen Moyer-Vanderburgh, Steven Buchsbaum, Eric Meshot, Melinda Jue and Kuang Jen Wu. The work is funded by the Chemical and Biological Technologies Department of the Defense Threat Reduction Agency.

Carbon Nanotubes: The Next Generation of Global Water Purification?

A typical day (maybe like yours) involves waking up, taking a 10 minute shower, cooking breakfast, running the dishwasher if it’s full, going to work, eating dinner with a refreshing glass of filtered water, and maybe tackling a load of laundry in the evening. None of these actions feel extravagant, but when I look at statistics of global water usage and the lack of fresh water availability, it’s obvious that as Americans, we consume significantly more gallons of water per day than anywhere else in the world. In fact, on average each American uses about 152 gallons of water daily, while people in some other countries such as Uganda and Haiti use only about 4 gallons.¹

That extreme low usage in some countries is not just because people are very conservation-minded – it is largely because there is not enough clean water to go around. Living in Wisconsin, I am conscientious of my water intake, but I am fortunate to not be in constant fear of turning on the faucet to see no water or even dirty water pouring out. Unfortunately, as we’ve learned from the recent experience of people in Flint, Michigan, it is not only countries outside the U.S. that have to worry about availability of clean water.

Personally, a trip to Israel last winter was what forced me to step out of my typical routine and experience firsthand how precious water is to their nation as a natural resource. My guide on the trip encouraged us to shower efficiently, never leave the water running while doing dishes, and to purchase bottled water, but to never waste a drop.

Enjoying the availability of fresh, clean water. (image by Elvert Barnes)

Being a scientist and an advocate for reducing my footprint on the environment, I wanted to learn more about what is being done to solve the problem of global freshwater availability. Considering what other recent medical and energy-related advancements have been made with the use of nanotechnology, it came as no surprise to me that carbon nanotubes (CNTs) are being studied as a means of water purification.

What exactly is a carbon nanotube? Picture a flat sheet of carbon atoms rolled into an incredibly tiny cylindrical tube with a diameter on the nanoscale, as shown here:

Carbon nanotube. (image from wikimedia commons)

These tiny, flexible, and surprisingly resilient materials may very well be our new direction in sustainable, large-scale water purification. The major advantage of CNTs is that water passes through them in a nearly frictionless manner due to something called hydrophobicity (i.e. preference to be away from water). But if CNTs are hydrophobic, you might wonder why water would even come near or enter them in the first place. This is an important point because water is a polar molecule and CNTs are non-polar, meaning they typically don’t want to mix together. One option for overcoming this is to coat the top of each tube with specific molecules that will initially attract water to the opening. Then, when water enters the nanotube, it flows through very quickly because it is being repelled by the hydrophobic tube walls. Conversely, most salts, ions, and pollutants won’t flow through the nanotube because they are attracted to and captured by the coating at the opening.

Also Read: Reusable carbon nanotubes could be the water filter of the future

Because water passes through the CNTs so easily and pollutants do not, CNTs have potential to be a great solution for water purification. If we’re able to use CNTs in the next generation of water purification technology, then we may be able to both desalinate (get rid of salt) and remove pollutants from otherwise unusable water around the world with less energy and less money than current methods require.

Improving water purification really is a global issue. On my trip last winter, I learned that Israel, along with other nations in the Middle East and Northern Africa, were already considered “water stressed” in 1995. This phrase indicates that the nation is withdrawing more than 25% of their renewable freshwater resources for agricultural, domestic, and industrial uses annually. By the year 2025 it is predicted that over 2.8 billion people in 48 countries will be “water stressed” or worse.² To combat this growing issue, countries are turning to unconventional options for wastewater treatment and desalination.

Freshwater stress map showing percentage ranges of how much water will be withdrawn with respect to amount naturally available.²

With a greater understanding of the problem at hand, let’s take a closer look at current techniques for water purification. Right now, the most common practice of cleansing salt water to produce freshwater is the use of desalination plants. These plants operate by the technique of reverse osmosis, which is shown in the figure below. Osmosis is when a less concentrated liquid (like fresh water) moves through a membrane toward a more concentrated liquid (water containing salt in this case). This process happens naturally without any need for applying external pressure. For reverse osmosis, we want the exact opposite to happen, and unlike osmosis, that requires an input of external energy. These semi-permeable reverse osmosis membranes that separate the two liquids are usually made of common organic materials with pores ranging from 0.3 to 0.6 nanometers in diameter. (As a comparison the diameter of a dime is 18,008,600 nanometers while the diameter of a water molecule is a mere 0.1 nm).

Differences between osmosis and reverse osmosis. (image by Emily Caudill)

As of 2013, there were over 17,000 plants worldwide providing more than 300 million people with desalinated water, many using reverse osmosis technology.³ Israel alone, with its relatively small land mass, has four plants with a fifth currently being built, while the U.S. houses about 250 plants.⁴

Desalination plants are effective, yet they are costly monetarily, energetically, and environmentally speaking. These plants require a great deal of energy input daily, and most desalination plants run on non-renewable energy sources (like fossil fuels and nuclear energy).⁵ With global freshwater availability declining, there is a need for cheaper, more efficient, and more environmentally sustainable desalination technology, and CNTs may be our most viable option looking forward. Their desalination capacity and frictionless water interaction means they require less energy than reverse osmosis to produce the same amount of fresh water.

Inside a reverse osmosis desalination plant  (image by James Grellier)

There are a few hurdles that must be overcome before we hear about the next “CNT desalination plant,” though. For example, we need to develop a method for large scale synthesis of CNTs that ensures consistent shape, size, and function. However, it is evident that our current methods of water purification aren’t enough and motivation is strong to develop this new use for CNTs.⁶

With increasing resources and technologies, we are closer than ever to a newer, faster, cheaper, and overall better way to provide fresh water on the global scale. Nanotechnology has proven to be a wonderful alternative to previously used methods in energy and medicine, for example, and we may be close to seeing a similar improvement in the case of water purification. As part of the Center for Sustainable Nanotechnology, I want to mention that it will be absolutely vital to produce and dispose of CNTs in a way that doesn’t lead to greater issues in the future (such as their own toxicity to the environment). This is an exciting time in science because we have groundbreaking approaches, but we are also in a day and age where we need to be more thoughtful about how our actions impact our finite supply of water, precious metals, and other vital resources.

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EDUCATIONAL RESOURCES

• Teach Engineering: Hands-On Activity: Water Filtration (grades 3-5)
• SafeWaterScience: Treatment of Water Teacher’s Guide (grades 5-8)
• National Nanotechnology Infrastructure Network: The Water Race: Hydrophobic & Hydrophilic Surfaces activity (high school)

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REFERENCES (may require subscription for full access)

1. The Water Information Program. Water Facts http://www.waterinfo.org/resources/water-facts.
2. United Nations Environment Program. Vital Water Graphics, retrieved from http://www.unep.org/dewa/vitalwater/article141.html.
3. International Desalination Association. Desalination by the Numbers http://idadesal.org/desalination-101/desalination-by-the-numbers/.
4. Texas Water Development Board. Seawater FAQs http://www.twdb.texas.gov/innovativewater/desal/faqseawater.asp.
5. Nuclear Energy Institue. Water Desalination
   http://www.nei.org/Knowledge-Center/Other-Nuclear-Energy-Applications/Water-Desalination
6. Das, R.; Ali, M. E.; Hamid, S. B. A.; Ramakrishna, S.; Chowdhury, Z. Z. Carbon nanotube membranes for water purification: a bright future in water desalination. Desalination, 2014, 336, 97-109. doi: 10.1016/j.desal.2013.12.026

NC State University has developed a Flexible Carbon Nanotube Film with a unique combination of thermal, electrical and physical properties that make it an an Excellent Candidate for Next-Generation of Smart Fabrics

Researchers reported in a new study that a material made of carbon nanotubes may be key in developing clothing that can heat or cool the wearer on demand. The film is twisted into a filament yarn and wound around a tube to show its flexibility. (Image: Kony Chatterjee) A film made of carbon nanotubes (CNT) may be a key material in developing clothing that can heat or cool the wearer on demand. A new North Carolina State University study finds that the CNT film has a combination of thermal, electrical and physical properties that make it an appealing candidate for next-generation smart fabrics.

The researchers were also able to optimize the thermal and electrical properties of the material, allowing the material to retain its desirable properties even when exposed to air for many weeks. Moreover, these properties were achieved using processes that were relatively simple and did not need excessively high temperatures.

“Many researchers are trying to develop a material that is non-toxic and inexpensive, but at the same time is efficient at heating and cooling,” said Tushar Ghosh, co-corresponding author of the study (ACS Applied Energy Materials, “In-plane Thermoelectric Properties of Flexible and Room Temperature Processable Doped Carbon Nanotube Films”). “Carbon nanotubes, if used appropriately, are safe, and we are using a form that happens to be inexpensive, relatively speaking. So it’s potentially a more affordable thermoelectric material that could be used next to the skin.” Ghosh is the William A. Klopman Distinguished Professor of Textiles in NC State’s Wilson College of Textiles.

“We want to integrate this material into the fabric itself,” said Kony Chatterjee, first author of the study and a Ph.D. student at NC State. “Right now, the research into clothing that can regulate temperature focuses heavily on integrating rigid materials into fabrics, and commercial wearable thermoelectric devices on the market aren’t flexible either.”

To cool the wearer, Chatterjee said, CNTs have properties that would allow heat to be drawn away from the body when an external source of current is applied.

“Think of it like a film, with cooling properties on one side of it and heating on the other,” Ghosh said.

The researchers measured the material’s ability to conduct electricity, as well as its thermal conductivity, or how easily heat passes through the material.

One of the biggest findings was that the material has relatively low thermal conductivity – meaning heat would not travel back to the wearer easily after leaving the body in order to cool it. That also means that if the material were used to warm the wearer, the heat would travel with a current toward the body, and not pass back out to the atmosphere.

The researchers were able to accurately measure the material’s thermal conductivity through a collaboration with the lab of Jun Liu, an assistant professor of mechanical and aerospace engineering at NC State. The researchers used a special experimental design to more accurately measure the material’s thermal conductivity in the direction that the electric current is moving within the material.

“You have to measure each property in the same direction to give you a reasonable estimate of the material’s capabilities,” said Liu, co-corresponding author of the study. “This was not an easy task; it was very challenging, but we developed a method to measure this, especially for thin flexible films.”

The research team also measured the ability of the material to generate electricity using a difference in temperature, or thermal gradient, between two environments. Researchers said that they could take advantage of this for heating, cooling, or to power small electronics.

Liu said that while these thermoelectric properties were important, it was also key that they found a material that was also flexible, stable in air, and relatively simple to make.

“The point of this paper isn’t that we achieved the best thermoelectric performance,” Liu said. “We achieved something that can be used as a flexible, electronic, soft material that’s easy to fabricate. It’s easy to prepare this material, and easy to achieve these properties.”

Ultimately, their vision for the project is to design a smart fabric that can heat and cool the wearer, along with energy harvesting. They believe that a smart garment could help reduce energy consumption.

“Instead of heating or cooling a whole dwelling or space, you would heat or cool the personal space around the body,” Ghosh said. “If we could get the thermostat down a degree or two, that could save a tremendous amount of energy.”

Source: North Carolina State University

Carbon Nanotube Second Skin Protects First Responders and Warfighters against Chem, Bio Agents – Lawrence Livermore National Laboratory

Published 8 May 2020

Recent events such as the COVID-19 pandemic and the use of chemical weapons in the Syria conflict have provided a stark reminder of the plethora of chemical and biological threats that soldiers, medical personnel and first responders face during routine and emergency operations. Researchers have developed a smart, breathable fabric designed to protect the wearer against biological and chemical warfare agents. Material of this type could be used in clinical and medical settings as well.

Recent events such as the COVID-19 pandemic and the use of chemical weapons in the Syria conflict have provided a stark reminder of the plethora of chemical and biological threats that soldiers, medical personnel and first responders face during routine and emergency operations.

Personnel safety relies on protective equipment which, unfortunately, still leaves much to be desired. For example, high breathability (i.e., the transfer of water vapor from the wearer’s body to the outside world) is critical in protective military uniforms to prevent heat-stress and exhaustion when soldiers are engaged in missions in contaminated environments.

The same materials (adsorbents or barrier layers) that provide protection in current garments also detrimentally inhibit breathability.

To tackle these challenges, a multi-institutional team of researchers led by Lawrence Livermore National Laboratory (LLNL) scientist Francesco Fornasiero has developed a smart, breathable fabric designed to protect the wearer against biological and chemical warfare agents. Material of this type could be used in clinical and medical settings as well.

The work was recently published online in Advanced Functional Materials and represents the successful completion of Phase I of the project, which is funded by the Defense Threat Reduction Agency through the Dynamic Multifunctional Materials for a Second Skin “D[MS]“ program.

“We demonstrated a smart material that is both breathable and protective by successfully combining two key elements: a base membrane layer comprising trillions of aligned carbon nanotube pores and a threat-responsive polymer layer grafted onto the membrane surface,” Fornasiero said.

LLNL notes that these carbon nanotubes (graphitic cylinders with diameters more than 5,000 times smaller than a human hair) could easily transport water molecules through their interiors while also blocking all biological threats, which cannot fit through the tiny pores.

This key finding was previously published in Advanced Materials.

The team has shown that the moisture vapor transport rate through carbon nanotubes increases with decreasing tube diameter and, for the smallest pore sizes considered in the study, is so fast that it approaches what one would measure in the bulk gas phase.

This trend is surprising and implies that single‐walled carbon nanotubes (SWCNTs) as moisture conductive pores overcome a limiting breathability/protection trade-off displayed by conventional porous materials, according to Fornasiero. Thus, size-sieving selectivity and water-vapor permeability can be simultaneously enhanced by decreasing SWCNT diameters.

Contrary to biological agents, chemical threats are smaller and can fit through the nanotube pores. To add protection against chemical hazards, a layer of polymer chains is grown on the material surface, which reversibly collapses in contact with the threat, thus temporarily blocking the pores.

“This dynamic layer allows the material to be ‘smart’ in that it provides protection only when and where it is needed,” said Timothy Swager, a collaborator at the Massachusetts Institute of Technology who developed the responsive polymer. These polymers were designed to transition from an extended to a collapsed state in contact with organophosphate threats, such as sarin. “We confirmed that both simulants and live agents trigger the desired volume change,” Swager added.

The team showed that the responsive membranes have enough breathability in their open-pore state to meet the sponsor requirements. In the closed state, the threat permeation through the material is dramatically reduced by two orders of magnitude. The demonstrated breathability and smart protection properties of this material are expected to translate in a significantly improved thermal comfort for the user and enable to greatly extend the wear time of protective gears, whether in a hospital or battlefield.

“The safety of warfighters, medical personnel and first responders during prolonged operations in hazardous environments relies on personal protective equipment that not only protects but also can breathe,” said Kendra McCoy, the DTRA program manager overseeing the project.

“DTRA Second Skin program is designed to address this need by supporting the development of new materials that adapt autonomously to the environment and maximize both comfort and protection for many hours.”

In the next phase of the project, the team will aim to incorporate on-demand protection against additional chemical threats and make the material stretchable for a better body fit, thus more closely mimicking the human skin.

MIT – A new approach to making airplane parts, minus the massive infrastructure

Carbon nanotube film produces aerospace-grade composites with no need for huge ovens or autoclaves.

A modern airplane’s fuselage is made from multiple sheets of different composite materials, like so many layers in a phyllo-dough pastry. Once these layers are stacked and molded into the shape of a fuselage, the structures are wheeled into warehouse-sized ovens and autoclaves, where the layers fuse together to form a resilient, aerodynamic shell.

Now MIT engineers have developed a method to produce aerospace-grade composites without the enormous ovens and pressure vessels. The technique may help to speed up the manufacturing of airplanes and other large, high-performance composite structures, such as blades for wind turbines.

The researchers detail their new method in a paper published today in the journal Advanced Materials Interfaces.

“If you’re making a primary structure like a fuselage or wing, you need to build a pressure vessel, or autoclave, the size of a two- or three-story building, which itself requires time and money to pressurize,” says Brian Wardle, professor of aeronautics and astronautics at MIT. “These things are massive pieces of infrastructure. Now we can make primary structure materials without autoclave pressure, so we can get rid of all that infrastructure.”

Wardle’s co-authors on the paper are lead author and MIT postdoc Jeonyoon Lee, and Seth Kessler of Metis Design Corporation, an aerospace structural health monitoring company based in Boston.

Out of the oven, into a blanket

In 2015, Lee led the team, along with another member of Wardle’s lab, in creating a method to make aerospace-grade composites without requiring an oven to fuse the materials together. Instead of placing layers of material inside an oven to cure, the researchers essentially wrapped them in an ultrathin film of carbon nanotubes (CNTs). When they applied an electric current to the film, the CNTs, like a nanoscale electric blanket, quickly generated heat, causing the materials within to cure and fuse together.

With this out-of-oven, or OoO, technique, the team was able to produce composites as strong as the materials made in conventional airplane manufacturing ovens, using only 1 percent of the energy.

The researchers next looked for ways to make high-performance composites without the use of large, high-pressure autoclaves — building-sized vessels that generate high enough pressures to press materials together, squeezing out any voids, or air pockets, at their interface.

“There’s microscopic surface roughness on each ply of a material, and when you put two plys together, air gets trapped between the rough areas, which is the primary source of voids and weakness in a composite,” Wardle says. “An autoclave can push those voids to the edges and get rid of them.”

Researchers including Wardle’s group have explored “out-of-autoclave,” or OoA, techniques to manufacture composites without using the huge machines. But most of these techniques have produced composites where nearly 1 percent of the material contains voids, which can compromise a material’s strength and lifetime. In comparison, aerospace-grade composites made in autoclaves are of such high quality that any voids they contain are neglible and not easily measured.

“The problem with these OoA approaches is also that the materials have been specially formulated, and none are qualified for primary structures such as wings and fuselages,” Wardle says. “They’re making some inroads in secondary structures, such as flaps and doors, but they still get voids.”

Straw pressure

Part of Wardle’s work focuses on developing nanoporous networks — ultrathin films made from aligned, microscopic material such as carbon nanotubes, that can be engineered with exceptional properties, including color, strength, and electrical capacity. The researchers wondered whether these nanoporous films could be used in place of giant autoclaves to squeeze out voids between two material layers, as unlikely as that may seem.

A thin film of carbon nanotubes is somewhat like a dense forest of trees, and the spaces between the trees can function like thin nanoscale tubes, or capillaries. A capillary such as a straw can generate pressure based on its geometry and its surface energy, or the material’s ability to attract liquids or other materials.

The researchers proposed that if a thin film of carbon nanotubes were sandwiched between two materials, then, as the materials were heated and softened, the capillaries between the carbon nanotubes should have a surface energy and geometry such that they would draw the materials in toward each other, rather than leaving a void between them. Lee calculated that the capillary pressure should be larger than the pressure applied by the autoclaves.

The researchers tested their idea in the lab by growing films of vertically aligned carbon nanotubes using a technique they previously developed, then laying the films between layers of materials that are typically used in the autoclave-based manufacturing of primary aircraft structures. They wrapped the layers in a second film of carbon nanotubes, which they applied an electric current to to heat it up. They observed that as the materials heated and softened in response, they were pulled into the capillaries of the intermediate CNT film.

The resulting composite lacked voids, similar to aerospace-grade composites that are produced in an autoclave. The researchers subjected the composites to strength tests, attempting to push the layers apart, the idea being that voids, if present, would allow the layers to separate more easily.

“In these tests, we found that our out-of-autoclave composite was just as strong as the gold-standard autoclave process composite used for primary aerospace structures,” Wardle says.

The team will next look for ways to scale up the pressure-generating CNT film. In their experiments, they worked with samples measuring several centimeters wide — large enough to demonstrate that nanoporous networks can pressurize materials and prevent voids from forming. To make this process viable for manufacturing entire wings and fuselages, researchers will have to find ways to manufacture CNT and other nanoporous films at a much larger scale.

“There are ways to make really large blankets of this stuff, and there’s continuous production of sheets, yarns, and rolls of material that can be incorporated in the process,” Wardle says.

He plans also to explore different formulations of nanoporous films, engineering capillaries of varying surface energies and geometries, to be able to pressurize and bond other high-performance materials.

“Now we have this new material solution that can provide on-demand pressure where you need it,” Wardle says. “Beyond airplanes, most of the composite production in the world is composite pipes, for water, gas, oil, all the things that go in and out of our lives. This could make making all those things, without the oven and autoclave infrastructure.”

This research was supported, in part, by Airbus, ANSYS, Embraer, Lockheed Martin, Saab AB, Saertex, and Teijin Carbon America through MIT’s Nano-Engineered Composite aerospace Structures (NECST) Consortium.

Macrocycles power up carbon nanotubes – applications in electronics and sensors – IMDEA

Interlocked molecules tune the electronic properties of nanotubes, allowing researchers to control their catalytic activity

Source: © M Eugenio Vázquez

Positive and negative regulation of carbon nanotube catalysts through encapsulation within macrocycles

Carbon nanotubes are a green alternative to metallic catalysts. However, tuning their activity relies on difficult and invasive chemical processes that normally damage the nanotubes’ structure. Now, only a few years after reporting the first mechanically interlocked nanotube derivatives,1 Emilio Pérez and his team at the IMDEA Nanoscience Institute in Madrid, Spain, have envisioned how to use these non-covalent modifications to power up the catalytic activity of carbon nanotubes.2

Source: © M Blanco et al, 2018, DOI: 10.1038/s41467-018-05183-8

The study encapsulated carbon nanotubes in different macrocycles then tested their catalytic activity

‘Carbon nanotubes have a hard time when they undergo chemical modification,’ explains Pérez. ‘We decided to give interlocked molecules a try, and it worked.’ The researchers mixed some single-walled nanotubes with U-shaped precursors of the macrocycles. Then, as soon as they added a tiny amount of Grubbs catalyst, the rings started surrounding the carbon nanotubes, so they end up covered in macrocyles.

Silvia Marchesan, who investigates carbon nanotubes at the University of Trieste, Italy, describes the strategy as sort of a chemical disguise: ‘You can think of dressing the nanotubes with clothes that temporarily alter their properties.’ She also highlights how clean the process is: ‘They manipulate carbon nanotubes threading them through the macrocycles, leaving the covalent structure of the tubes unaltered.’

Because of their non-covalent nature, Pérez likes to compare these new catalysts to enzymes, ‘although their mechanism of action is totally different’. ‘The macrocycles modify the electronic properties of the nanotube without interfering with the catalytic site – the “naked” carbon nanotubes walls,’ he explains. As a proof of concept, Pérez’s team used their catalysts to reduce nitroarenes. ‘Electron-withdrawing macrocycles slow the reaction down, while electron donor rings quicken it,’ says Pérez. ‘In some examples, the reaction is accelerated up to 15 times its normal speed.’

The interlocked macrocycles also impede the aggregation of carbon nanotubes, which could also boost their catalytic performance. However, Marchesan believes that ‘the trends in enhancement or reduction of the catalytic activity clearly show an effect due to the electronic effects of the macrocycles involved.’ The fact that the interlocked molecules impede aggregation is just ‘a nice additional property to get the best performance out of the nanotubes,’ she adds.

‘Controlling the electronic properties of nanotubes could have implications beyond catalysis,’ explains Pérez. ‘We could engineer modified carbon nanotubes on demand, which could find applications in electronics and sensors,’ he adds. ‘The technique shows great promise, because you have very stable products while keeping the high-surface structure of the nanotubes.’ Marchesan also dreams about the possibilities of mechanically interlocked nanotubes: ‘It is an interesting approach to build complex supramolecular architectures, for instance to create on–off switches.’

References

1. A de Juan et al, Angew. Chem. Int. Ed., 2014, 53, 5394 (DOI: 10.1002/anie.201402258)

2. M Blanco et al, Nat. Commun., 2018, 9, 2671 (DOI: 10.1038/s41467-018-05183-8)

Programmable and Highly Scalable Molecular Fabrication of Trillions of Carbon-Nanotubes (CNT’s) for: Carbon-zero fuels, health & performance optimized air, water and precision medicine

Mattershift designs and manufactures nanotube membranes carbon-zero fuels, health and performance optimized air and water, and precision medicine.

ThOe startup was founded in 2013 to realize the potential of molecular factories, with the ultimate goal of printing matter from the air.

Science Advances – Large-scale polymeric carbon nanotube membranes with sub–1.27-nm pores

Abstract

Mattershift reports the first characterization study of commercial prototype carbon nanotube (CNT) membranes consisting of sub–1.27-nm-diameter CNTs traversing a large-area nonporous polysulfone film. The membranes show rejection of NaCl and MgSO4 at higher ionic strengths than have previously been reported in CNT membranes, and specific size selectivity for analytes with diameters below 1.24 nm. The CNTs used in the membranes were arc discharge nanotubes with inner diameters of 0.67 to 1.27 nm. Water flow through the membranes was 1000 times higher than predicted by Hagen-Poiseuille flow, in agreement with previous CNT membrane studies. Ideal gas selectivity was found to deviate significantly from that predicted by both viscous and Knudsen flow, suggesting that surface diffusion effects may begin to dominate gas selectivity at this size scale.

The most basic building block of a Mattershift Molecular Factory is the Programmable Molecular Gateway. It consists of a carbon nanotube fixed within a flexible polymer sheet and aligned so that both of its ends are open.

The gateways are called “programmable” because a great variety of gates can be added to their openings, allowing them to manipulate molecules in specific ways.

One example is a NEMS gate, which is a gateway with a Nano Electro Mechanical System (NEMS) attached. It’s similar to a Micro Electro Mechanical System (MEMS), like the kind used to create accelerometers in smartphones, for example, but NEMS are much smaller. The one shown above is a gate that can be opened and closed by sending an electrical signal through the nanotube to which it’s attached.

Another example is a catalyst gate. This is a gateway with a catalyst attached to the opening of the nanotube. All molecules passing through the gateway must interact with the catalyst, which may be active or passive, removing or adding electrons, combining or splitting molecular parts.

Protein gates may be used to allow only specific molecules to pass through the gateways, like therapeutically useful antibodies, ions, or anything else protein channels may select for. Protein gates consisting of enzymes may also be used for highly specific catalysis of reactions, like those involved in molecular assembly.

A great many types of gates are possible, and many have already been demonstrated in laboratories around the world

Each sheet is embedded with a large number of gateways to transform and transport molecules. A typical density of gateways is 250 Trillion per square meter of sheet.

By creating a series of gateway sheets that perform different functions — purification, catalysis, separation, concentration, further reactions, and so on, complex chemical synthesis can be achieved in compact, inexpensive devices. These factories may be as small as a shoebox or as large as a warehouse.

The key innovation at Mattershift has been to create an inexpensive and scalable platform for this library of gates. With the ability to deploy Programmable Molecular Gateways at scale, we believe practical molecular factories are now possible.

New York-based Mattershift has managed to create large-scale carbon nanotube (CNT) membranes that are able to combine and separate individual molecules.

MIT: Optimizing carbon nanotube electrodes for energy storage and water desalination applications

Evelyn Wang (left) and Heena Mutha have developed a nondestructive method of quantifying the detailed characteristics of carbon nanotube (CNT) samples — a valuable tool for optimizing these materials for use as electrodes in a variety of practical devices. Photo: Stuart Darsch

New model measures characteristics of carbon nanotube structures for energy storage and water desalination applications.

Using electrodes made of carbon nanotubes (CNTs) can significantly improve the performance of devices ranging from capacitors and batteries to water desalination systems. But figuring out the physical characteristics of vertically aligned CNT arrays that yield the most benefit has been difficult.

Now an MIT team has developed a method that can help. By combining simple benchtop experiments with a model describing porous materials, the researchers have found they can quantify the morphology of a CNT sample, without destroying it in the process.

In a series of tests, the researchers confirmed that their adapted model can reproduce key measurements taken on CNT samples under varying conditions. They’re now using their approach to determine detailed parameters of their samples — including the spacing between the nanotubes — and to optimize the design of CNT electrodes for a device that rapidly desalinates brackish water.

A common challenge in developing energy storage devices and desalination systems is finding a way to transfer electrically charged particles onto a surface and store them there temporarily. In a capacitor, for example, ions in an electrolyte must be deposited as the device is being charged and later released when electricity is being delivered. During desalination, dissolved salt must be captured and held until the cleaned water has been withdrawn.

One way to achieve those goals is by immersing electrodes into the electrolyte or the saltwater and then imposing a voltage on the system. The electric field that’s created causes the charged particles to cling to the electrode surfaces. When the voltage is cut, the particles immediately let go.

“Whether salt or other charged particles, it’s all about adsorption and desorption,” says Heena Mutha PhD ’17, a senior member of technical staff at the Charles Stark Draper Laboratory. “So the electrodes in your device should have lots of surface area as well as open pathways that allow the electrolyte or saltwater carrying the particles to travel in and out easily.”

One way to increase the surface area is by using CNTs. In a conventional porous material, such as activated charcoal, interior pores provide extensive surface area, but they’re irregular in size and shape, so accessing them can be difficult. In contrast, a CNT “forest” is made up of aligned pillars that provide the needed surfaces and straight pathways, so the electrolyte or saltwater can easily reach them.

However, optimizing the design of CNT electrodes for use in devices has proven tricky. Experimental evidence suggests that the morphology of the material — in particular, how the CNTs are spaced out — has a direct impact on device performance. Increasing the carbon concentration when fabricating CNT electrodes produces a more tightly packed forest and more abundant surface area. But at a certain density, performance starts to decline, perhaps because the pillars are too close together for the electrolyte or saltwater to pass through easily.

Designing for device performance

“Much work has been devoted to determining how CNT morphology affects electrode performance in various applications,” says Evelyn Wang, the Gail E. Kendall Professor of Mechanical Engineering. “But an underlying question is, ‘How can we characterize these promising electrode materials in a quantitative way, so as to investigate the role played by such details as the nanometer-scale interspacing?'”

Inspecting a cut edge of a sample can be done using a scanning electron microscope (SEM). But quantifying features, such as spacing, is difficult, time-consuming, and not very precise. Analyzing data from gas adsorption experiments works well for some porous materials, but not for CNT forests. Moreover, such methods destroy the material being tested, so samples whose morphologies have been characterized can’t be used in tests of overall device performance.

For the past two years, Wang and Mutha have been working on a better option. “We wanted to develop a nondestructive method that combines simple electrochemical experiments with a mathematical model that would let us ‘back calculate’ the interspacing in a CNT forest,” Mutha says. “Then we could estimate the porosity of the CNT forest — without destroying it.”

Adapting the conventional model

One widely used method for studying porous electrodes is electrochemical impedance spectroscopy (EIS). It involves pulsing voltage across electrodes in an electrochemical cell at a set time interval (frequency) while monitoring “impedance,” a measure that depends on the available storage space and resistance to flow. Impedance measurements at different frequencies is called the “frequency response.”

The classic model describing porous media uses that frequency response to calculate how much open space there is in a porous material. “So we should be able to use [the model] to calculate the space between the carbon nanotubes in a CNT electrode,” Mutha says.

But there’s a problem: This model assumes that all pores are uniform, cylindrical voids. But that description doesn’t fit electrodes made of CNTs. Mutha modified the model to more accurately define the pores in CNT materials as the void spaces surrounding solid pillars. While others have similarly altered the classic model, Mutha took her alterations a step further. The nanotubes in a CNT material are unlikely to be packed uniformly, so she added to her equations the ability to account for variations in the spacing between the nanotubes. With this modified model, Mutha could analyze EIS data from real samples to calculate CNT spacings.

Using the model

To demonstrate her approach, Mutha first fabricated a series of laboratory samples and then measured their frequency response. In collaboration with Yuan “Jenny” Lu ’15, a materials science and engineering graduate, she deposited thin layers of aligned CNTs onto silicon wafers inside a furnace and then used water vapor to separate the CNTs from the silicon, producing free-standing forests of nanotubes. To vary the CNT spacing, she used a technique developed by MIT collaborators in the Department of Aeronautics and Astronautics, Professor Brian Wardle and postdoc associate Itai Stein PhD ’16. Using a custom plastic device, she mechanically squeezed her samples from four sides, thereby packing the nanotubes together more tightly and increasing the volume fraction — that is, the fraction of the total volume occupied by the solid CNTs.

To test the frequency response of the samples, she used a glass beaker containing three electrodes immersed in an electrolyte. One electrode is the CNT-coated sample, while the other two are used to monitor the voltage and to absorb and measure the current. Using that setup, she first measured the capacitance of each sample, meaning how much charge it could store in each square centimeter of surface area at a given constant voltage. She then ran EIS tests on the samples and analyzed results using her modified porous media model.

Results for the three volume fractions tested show the same trends. As the voltage pulses become less frequent, the curves initially rise at about a 45 degree slope. But at some point, each one shifts toward vertical, with resistance becoming constant and impedance continuing to rise.

As Mutha explains, those trends are typical of EIS analyses. “At high frequencies, the voltage changes so quickly that — because of resistance in the CNT forest — it doesn’t penetrate the depth of the entire electrode material, so the response comes only from the surface or partway in,” she says. “But eventually the frequency is low enough that there’s time between pulses for the voltage to penetrate and for the whole sample to respond.”

Resistance is no longer a noticeable factor, so the line becomes vertical, with the capacitance component causing impedance to rise as more charged particles attach to the CNTs. That switch to vertical occurs earlier with the lower-volume-fraction samples. In sparser forests, the spaces are larger, so the resistance is lower.

The most striking feature of Mutha’s results is the gradual transition from the high-frequency to the low-frequency regime. Calculations from a model based on uniform spacing — the usual assumption — show a sharp transition from partial to complete electrode response. Because Mutha’s model incorporates subtle variations in spacing, the transition is gradual rather than abrupt. Her experimental measurements and model results both exhibit that behavior, suggesting that the modified model is more accurate.

By combining their impedance spectroscopy results with their model, the MIT researchers inferred the CNT interspacing in their samples. Since the forest packing geometry is unknown, they performed the analyses based on three- and six-pillar configurations to establish upper and lower bounds. Their calculations showed that spacing can range from 100 nanometers in sparse forests to below 10 nanometers in densely packed forests.

Comparing approaches

Work in collaboration with Wardle and Stein has validated the two groups’ differing approaches to determining CNT morphology. In their studies, Wardle and Stein use an approach similar to Monte Carlo modeling, which is a statistical technique that involves simulating the behavior of an uncertain system thousands of times under varying assumptions to produce a range of plausible outcomes, some more likely than others. For this application, they assumed a random distribution of “seeds” for carbon nanotubes, simulated their growth, and then calculated characteristics, such as inter-CNT spacing with an associated variability. Along with other factors, they assigned some degree of waviness to the individual CNTs to test the impact on the calculated spacing.

To compare their approaches, the two MIT teams performed parallel analyses that determined average spacing at increasing volume fractions. The trends they exhibited matched well, with spacing decreasing as volume fraction increases. However, at a volume fraction of about 26 percent, the EIS spacing estimates suddenly go up — an outcome that Mutha believes may reflect packing irregularities caused by buckling of the CNTs as she was densifying them.

To investigate the role played by waviness, Mutha compared the variabilities in her results with those in Stein’s results from simulations assuming different degrees of waviness. At high volume fractions, the EIS variabilities were closest to those from the simulations assuming little or no waviness. But at low volume fractions, the closest match came from simulations assuming high waviness.

Based on those findings, Mutha concludes that waviness should be considered when performing EIS analyses — at least in some cases. “To accurately predict the performance of devices with sparse CNT electrodes, we may need to model the electrode as having a broad distribution of interspacings due to the waviness of the CNTs,” she says. “At higher volume fractions, waviness effects may be negligible, and the system can be modeled as simple pillars.”

The researchers’ nondestructive yet quantitative technique provides device designers with a valuable new tool for optimizing the morphology of porous electrodes for a wide range of applications. Already, Mutha and Wang have been using it to predict the performance of supercapacitors and desalination systems. Recent work has focused on designing a high-performance, portable device for the rapid desalination of brackish water. Results to date show that using their approach to optimize the design of CNT electrodes and the overall device simultaneously can as much as double the salt adsorption capacity of the system, while speeding up the rate at which clean water is produced.

This research was supported in part by the MIT Energy Initiative Seed Fund Program and by the King Fahd University of Petroleum and Minerals (KFUPM) in Dhahran, Saudi Arabia, through the Center for Clean Water and Clean Energy at MIT and KFUPM. Mutha’s work was supported by a National Science Foundation Graduate Research Fellowship and Stein’s work by the Department of Defense through the National Defense Science and Engineering Graduate Fellowship Program.

Rice – MD Anderson use Fluorescent Carbon Nanotube probes to detect ovarian cancer – Achieve first In – Vivo Success

 

 

Abstract:
Researchers at Rice University and the University of Texas MD Anderson Cancer Center have refined and, for the first time, run in vivo tests of a method that may allow nanotube-based probes to locate specific tumors in the body. Their ability to pinpoint tumors with sub-millimeter accuracy could eventually improve early detection and treatment of ovarian cancer.

The noninvasive technique relies on single-walled carbon nanotubes that can be optically triggered to emit shortwave infrared light. The Rice lab of chemist Bruce Weisman, a pioneer in the discovery and interpretation of the phenomenon, reported the new results in the American Chemical Society journal ACS Applied Materials and Interfaces.

For this study, the researchers used the technique to pinpoint small concentrations of nanotubes inside rodents. The lab of co-author Dr. Robert Bast Jr., an expert in ovarian cancer and vice president for translational research at MD Anderson, inserted gel-bound carbon nanotubes into the ovaries of rodents to mimic the accumulations that are expected for nanotubes linked to special antibodies that recognize tumor cells. The rodents were then scanned with the Rice lab’s custom-built optical device to detect the faint emission signatures of as little as 100 picograms of nanotubes.

The device irradiated the rodents with intense red light from an array of light-emitting diodes and read fluorescent signals with a specialized sensitive detector. Because different types of tissue absorb emissions from the nanotubes differently, the scanner took readings from many locations to triangulate the tumor’s exact location, as confirmed by later MRI scans.

Weisman said it should be possible to noninvasively find small ovarian tumors within rodents used for medical research by linking nanotubes to antibody biomarkers and administering the biomarkers intravenously. The biomarkers would accumulate at the tumor site. He said more refined versions of the optical scanner may then be able to locate a tumor within seconds, and further advances may extend the method’s application to human cancer detection. The new results suggested that antibody-nanotube probes could potentially detect tumors with as few as 100 ovarian cancer cells, which could make it a valuable tool for early detection. 

Rice graduate student Ching-Wei Lin is lead author of the paper. Co-authors from the Bast group at MD Anderson are researcher Dr. Hailing Yang and senior research assistants Weiqun Mao and Lan Pang. Rice co-authors are chemistry graduate student Stephen Sanchez and Kathleen Beckingham, a professor of biosciences.

The research was supported by the National Science Foundation, the Welch Foundation, the National Institutes of Health, the John S. Dunn Foundation Collaborative Research Award Program, the National Cancer Institute, the Cancer Prevention and Research Institute of Texas, the National Foundation for Cancer Research, the Mossy Foundation, Golfers Against Cancer, the Roberson Endowment and Stuart and Gaye Lynn Zarrow.

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About Rice University
Located on a 300-acre forested campus in Houston, Rice University is consistently ranked among the nation’s top 20 universities by U.S. News & World Report. Rice has highly respected schools of Architecture, Business, Continuing Studies, Engineering, Humanities, Music, Natural Sciences and Social Sciences and is home to the Baker Institute for Public Policy.

Rice U: Long Nanotube fibers for use in Large-Scale Aerospace, Consumer Electronics and Textile Applications

Rice University researchers advance characterization, purification of Nanotube wires and films

RICE UNIVERSITY

To make continuous, strong and conductive carbon nanotube fibers, it’s best to start with long nanotubes, according to scientists at Rice University.

The Rice lab of chemist and chemical engineer Matteo Pasquali, which demonstrated its pioneering method to spin carbon nanotube into fibers in 2013, has advanced the art of making nanotube-based materials with two new papers in the American Chemical Society’s ACS Applied Materials and Interfaces.

The first paper characterized 19 batches of nanotubes produced by as many manufacturers to determine which nanotube characteristics yield the most conductive and strongest fibers for use in large-scale aerospace, consumer electronics and textile applications.

The researchers determined the nanotubes’ aspect ratio — length versus width — is a critical factor, as is the overall purity of the batch. They found the tubes’ diameters, number of walls and crystalline quality are not as important to the product properties.

Pasquali said that while the aspect ratio of nanotubes was known to have an influence on fiber properties, this is the first systematic work to establish the relationship across a broad range of nanotube samples. Researchers found that longer nanotubes could be processed as well as shorter ones, and that mechanical strength and electrical conductivity increased in lockstep.

The best fibers had an average tensile strength of 2.4 gigapascals (GPa) and electrical conductivity of 8.5 megasiemens per meter, about 15 percent of the conductivity of copper. Increasing nanotube length during synthesis will provide a path toward further property improvements, Pasquali said.

The second paper focused on purifying fibers produced by the floating catalyst method for use in films and aerogels. This process is fast, efficient and cost-effective on a medium scale and can yield the direct spinning of high-quality nanotube fibers; however, it leaves behind impurities, including metallic catalyst particles and bits of leftover carbon, allows less control of fiber structure and limits opportunities to scale up, Pasquali said.

“That’s where these two papers converge,” he said. “There are basically two ways to make nanotube fibers. In one, you make the nanotubes and then you spin them into fibers, which is what we’ve developed at Rice. In the other, developed at the University of Cambridge, you make nanotubes in a reactor and tune the reactor such that, at the end, you can pull the nanotubes out directly as fibers.

“It’s clear those direct-spun fibers include longer nanotubes, so there’s an interest in getting the tubes included in those fibers as a source of material for our spinning method,” Pasquali said. “This work is a first step toward that goal.”

The reactor process developed a decade ago by materials scientist Alan Windle at the University of Cambridge produces the requisite long nanotubes and fibers in one step, but the fibers must be purified, Pasquali said. Researchers at Rice and the National University of Singapore (NUS) have developed a simple oxidative method to clean the fibers and make them usable for a broader range of applications.

The labs purified fiber samples in an oven, first burning out carbon impurities in air at 500 degrees Celsius (932 degrees Fahrenheit) and then immersing them in hydrochloric acid to dissolve iron catalyst impurities.

Impurities in the resulting fibers were reduced to 5 percent of the material, which made them soluble in acids. The researchers then used the nanotube solution to make conductive, transparent thin films.

“There is great potential for these disparate techniques to be combined to produce superior fibers and the technology scaled up for industrial use,” said co-author Hai Minh Duong, an NUS assistant professor of mechanical engineering. “The floating catalyst method can produce various types of nanotubes with good morphology control fairly quickly. The nanotube filaments can be collected directly from their aerogel formed in the reactor. These nanotube filaments can then be purified and twisted into fibers using the wetting technique developed by the Pasquali group.”

Pasquali noted the collaboration between Rice and Singapore represents convergence of another kind. “This may well be the first time someone from the Cambridge fiber spinning line (Duong was a postdoctoral researcher in Windle’s lab) and the Rice fiber spinning line have converged,” he said. “We’re working together to try out materials made in the Cambridge process and adapting them to the Rice process.”

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Alumnus Dmitri Tsentalovich, currently an academic visitor at Rice, is lead author of the characterization paper. Co-authors are graduate students Robert Headrick and Colin Young, research scientist Francesca Mirri and alumni Junli Hao and Natnael Behabtu, all of Rice.

Thang Tran of Rice and NUS and Headrick are co-lead authors of the catalyst paper. Co-authors are graduate student Amram Bengio and research specialist Vida Jamali, both of Rice, and research scientist Sandar Myo and graduate student Hamed Khoshnevis, both of NUS.

The Air Force Office of Scientific Research, the Welch Foundation and NASA supported both projects. The characterization project received additional support from the Department of Energy. The catalyst project received additional support from the Temasek Laboratory in Singapore.

Influence of Carbon Nanotube Characteristics on Macroscopic Fiber Properties: http://pubs.acs.org/doi/abs/10.1021/acsami.7b10968

Purification and Dissolution of Carbon Nanotube Fibers Spun from Floating Catalyst Method: http://pubs.acs.org/doi/abs/10.1021/acsami.7b09287

This news release can be found online at http://news.rice.edu/2017/10/15/long-nanotubes-make-strong-fibers/

What Are Carbon Nanotubes and What are some of their Applications

Carbon nanotubes (CNTs) are allotropes of carbon with a cylindrical nanostructure.

 

 

 

These cylindrical carbonmolecules have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. Owing to the material’s exceptional strength and stiffness, nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1,^[1] significantly larger than for any other material.

In addition, owing to their extraordinary thermal conductivity, mechanical, and electrical properties, carbon nanotubes find applications as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber) baseball bats, golf clubs, car parts or damascus steel.