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)

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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


Opt CNTs for Water Wang-Mutha-nanotubes_0Evelyn 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

OPT CNTs III graphic-1

“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.”Opt CNTs II 1-newmodelmeas

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


 

 

Rice CNTs 57f79f2812948

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.

Rice Optical Sensor CNTs 0523_SPECTRAL-1-web-txhgun

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 MD Anderson Cancer CNTs 54864

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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Rice logo_rice3

 

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-carbon-nanotube-thread-wet-spinning

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.Rice II nanotubes

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.”

Q Flow MODEL-OF-CARBON-NANOTUBE-PAIDThe 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/

1-blind CNTWhat 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 nanotechnologyelectronicsoptics 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.

 

UC Riverside: Squeezing every drop (almost 100%) of fresh water from waste brine (salt solutions)


squeezingeveHot brines used in traditional membrane distillation systems are highly corrosive, making the heat exchangers and other system elements expensive, and limiting water recovery (a). To improve this, UCR researchers developed a self-heating …more

Engineers at the University of California, Riverside have developed a new way to recover almost 100 percent of the water from highly concentrated salt solutions. The system will alleviate water shortages in arid regions and reduce concerns surrounding high salinity brine disposal, such as hydraulic fracturing waste.

The research, which involves the development of a carbon nanotube-based heating element that will vastly improve the recovery of fresh during membrane distillation processes, was published today in the journal Nature Nanotechnology. David Jassby, an assistant professor of chemical and environmental engineering in UCR’s Bourns College of Engineering, led the project.

While reverse osmosis is the most common method of removing salt from seawater, wastewater, and brackish water, it is not capable of treating highly concentrated salt solutions. Such solutions, called brines, are generated in massive amounts during reverse osmosis (as waste products) and hydraulic fracturing (as produced water), and must be disposed of properly to avoid environmental damage. In the case of , produced water is often disposed of underground in injection wells, but some studies suggest this practice may result in an increase in local earthquakes.

One way to treat brine is membrane distillation, a thermal desalination technology in which heat drives water vapor across a membrane, allowing further water recovery while the salt stays behind. However, hot brines are highly corrosive, making the heat exchangers and other system elements expensive in traditional membrane distillation systems. Furthermore, because the process relies on the heat capacity of water, single pass recoveries are quite low (less than 10 percent), leading to complicated heat management requirements.

“In an ideal scenario, thermal desalination would allow the recovery of all the water from brine, leaving behind a tiny amount of a solid, crystalline salt that could be used or disposed of,” Jassby said. “Unfortunately, current processes rely on a constant feed of hot brine over the membrane, which limits water recovery across the membrane to about 6 percent.”

To improve on this, the researchers developed a self-heating carbon nanotube-based membrane that only heats the brine at the membrane surface. The new system reduced the heat needed in the process and increased the yield of recovered water to close to 100 percent.

In addition to the significantly improved desalination performance, the team also investigated how the application of alternating currents to the heating element could prevent degradation of the carbon nanotubes in the saline environment. Specifically, a threshold frequency was identified where electrochemical oxidation of the nanotubes was prevented, allowing the nanotube films to be operated for significant lengths of time with no reduction in performance. The insights provided by this work will allow carbon nanotube-based heating elements to be used in other applications where electrochemical stability of the nanotubes is a concern.

Explore further: Researchers develop hybrid nuclear desalination technique with improved efficiency

More information: Frequency-dependent stability of CNT Joule heaters in ionizable media and desalination processes, Nature Nanotechnology, nature.com/articles/doi:10.1038/nnano.2017.102

 

Making Solar Cells Obsolete with GIT’s Optical ‘Rectenna’ Technology ~ 40% to 90% Conversion Effciency: YouTube Video


Optical Rectenna download

Georgia Tech Professor of Mechanical Engineering, Dr. Bara Cola, shares how his childhood dreams of playing professional football turned into an exciting research career and important nanoengineering innovations. Dr. Cola’s breakthrough optical rectenna technology can be viewed here https://smartech.gatech.edu/handle/18….”

Watch the YouTube Video:

 

e9cf3-nanorectannaA new kind of nanoscale rectenna (half antenna and half rectifier) can convert solar and infrared into electricity, plus be tuned to nearly any other frequency as a detector.

Right now efficiency is only one percent, but professor Baratunde Cola and colleagues at the Georgia Institute of Technology (Georgia Tech, Atlanta) convincingly argue that they can achieve 40 percent broad spectrum efficiency (double that of silicon and more even than multi-junction gallium arsenide) at a one-tenth of the cost of conventional solar cells (and with an upper limit of 90 percent efficiency for single wavelength conversion).

It is well suited for mass production, according to Cola. It works by growing fields of carbon nanotubes vertically, the length of which roughly matches the wavelength of the energy source (one micron for solar), capping the carbon nanotubes with an insulating dielectric (aluminum oxide on the tethered end of the nanotube bundles), then growing a low-work function metal (calcium/aluminum) on the dielectric and voila–a rectenna with a two electron-volt potential that collects sunlight and converts it to direct current (DC).

“Our process uses three simple steps: grow a large array of nanotube bundles vertically; coat one end with dielectric; then deposit another layer of metal,” Cola told EE Times. “In effect we are using one end of the nanotube as a part of a super-fast metal-insulator-metal tunnel diode, making mass production potentially very inexpensive up to 10-times cheaper than crystalline silicon cells.”

Read the full Article Here: Solar Cells Will be Made Obsolete by 3D rectennas aiming at 40-to-90% efficiency

 

NASA and Rice U Collaborate on’Fuzzy Fibers’ (carbide nanotubes) that can take the Heat from NextGen Rockets


Space X Rocket 31E1F88F00000578-3477542-image-a-8_1457192298353Researchers create tough material for next generation of powerful engines

To stand up to the heat and pressure of next-generation rocket engines, the composite fibers used to make them should be fuzzy.

The Rice University laboratory of materials scientist Pulickel Ajayan, in collaboration with NASA, has developed “fuzzy fibers” of silicon carbide that act like Velcro and stand up to the punishment that materials experience in aerospace applications.

Fuzzy Fibers Rice NASA 170330153941_1_540x360Silicon carbide nanotubes attached to separate silicon carbide fibers, used by NASA, entangle each other in this electron microscope image. The material created at Rice University is intended for a ceramic composite that would make rocket engines stronger, lighter and better able to withstand extreme heat.
Credit: Ajayan Research Group/Rice University

 

 

The fibers strengthen composites used in advanced rocket engines that have to withstand temperatures up to 1,600 degrees Celsius (2,912 degrees Fahrenheit). Ceramic composites in rockets now being developed use silicon carbide fibers to strengthen the material, but they can crack or become brittle when exposed to oxygen.

The Rice lab embedded silicon carbide nanotubes and nanowires into the surface of NASA’s fibers. The exposed parts of the fibers are curly and act like the hooks and loops that make Velcro so valuable — but on the nanoscale.

The result, according to lead researchers Amelia Hart, a Rice graduate student, and Chandra Sekhar Tiwary, a Rice postdoctoral associate, creates very strong interlocking connections where the fibers tangle; this not only makes the composite less prone to cracking but also seals it to prevent oxygen from changing the fiber’s chemical composition.

The work is detailed in the American Chemical Society journal Applied Materials and Interfaces.

The work began when Hart, who had been studying the growth of carbon nanotubes on ceramic wool, met Michael Meador, then a scientist at NASA’s Glenn Research Center, Cleveland, at the kickoff reception for Rice’s Materials Science and NanoEngineering Department. (Meador is now nanotechnology project manager at NASA’s Game Changing Technologies program.)

That led to a fellowship in Cleveland and the chance to combine her ideas with those of NASA research engineer and paper co-author Janet Hurst. “She was partially converting silicon carbide from carbon nanotubes,” Hart said. “We used her formulation and my ability to grow nanotubes and figured out how to make the new composite.”

Back at Rice, Hart and her colleagues grew their hooks and loops by first bathing silicon carbide fiber in an iron catalyst and then using water-assisted chemical vapor deposition, a process developed in part at Rice, to embed a carpet of carbon nanotubes directly into the surface. These become the template for the final product. The fibers were then heated in silicon nanopowder at high temperature, which converts the carbon nanotubes to silicon carbide “fuzz.”

The researchers hope their fuzzy fibers will upgrade the strong, light and heat-resistant silicon carbide fibers that, when put in ceramic composites, are being tested for robust nozzles and other parts in rocket engines. “The silicon carbide fiber they already use is stable to 1,600 C,” Tiwary said. “So we’re confident that attaching silicon carbide nanotubes and wires to add strength will make it even more cutting-edge.”

The new materials should also make entire turbo engines significantly lighter, Hart said. “Before they used silicon carbide composites, many engine parts were made of nickel superalloys that had to incorporate a cooling system, which added weight to the whole thing,” she said. “By switching to ceramic matrix composites, they could take out the cooling system and go to higher temperatures. Our material will allow the creation of larger, longer-lasting turbo jet engines that go to higher temperatures than ever before.”

Friction and compression testing showed the lateral force needed to move silicon carbide nanotubes and wires over each other was much greater than that needed to slide past either plain nanotubes or unenhanced fibers, the researchers reported. They were also able to easily bounce back from high compression applied with a nano-indenter, which showed their ability to resist breaking down for longer amounts of time.

Tests to see how well the fibers handled heat showed plain carbon nanotubes burning away from the fibers, but the silicon carbide nanotubes easily resisted temperatures of up to 1,000 C.

Hart said the next step will be to apply her conversion techniques to other carbon nanomaterials to create unique three-dimensional materials for additional applications.


Story Source:

Materials provided by Rice University. Note: Content may be edited for style and length.


Journal Reference:

  1. Amelia H.C. Hart, Ryota Koizumi, John T Hamel, Peter Samora Owuor, Yusuke Ito, Sehmus Ozden, Sanjit Bhowmick, Syed Asif Syed Amanulla, Thierry Tsafack, Kunttal Keyshar, Rahul Mital, Janet Hurst, Robert Vajtai, Chandra Sekhar Tiwary, Pulickel M Ajayan. Velcro®-Inspired SiC Fuzzy Fibers for Aerospace Applications. ACS Applied Materials & Interfaces, 2017; DOI: 10.1021/acsami.7b01378

 

Nanotube-based Li-ion Batteries Can Charge to Near Maximum in Two Minutes but …


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Nanotube-based Li-ion Batteries Can Charge to Near Maximum in Two Minutes … but could our current grid system handle an ‘en masse’ switch to EV’s?

The prospects for ubiquitous all-electric vehicles (EVs) powered by lithium-ion (Li-ion) batteries took a bit of a hit back in 2010, when then U.S. Secretary of Energy Steven Chu addressed the United Nations Climate Change Conference in Cancun and suggested that, for battery powered cars to replace those powered by fossil fuels, some pretty significant improvements would need to be made to current technology.

Chu said at the time: “It will take a battery, first that can last for 15 years of deep discharges. You need about five as a minimum, but really six- or seven-times higher storage capacity and you need to bring the price down by about a factor of three.” Chu suggested it might take another five years before such a battery would be developed, and he was almost exactly right in his prediction.

Researchers at the Nanyang Technology University (NTU) in Singapore have achieved at least some of those criteria by developing a Li-ion battery capable of 20 years of deep discharges, more than 10 times that of existing Li-ion batteries.

In addition to longer battery life, the new battery design can be charged up quickly so that it can reach 70 percent of its maximum charge in just two minutes.

These features tick at least two of the metrics that Chu and others have indicated are key to making all-EVs compete with those running on fossil fuels. This would mean that EV owners would not have to spend roughly $5000 every two years for a completely new set of batteries. It could also allow for a quick stop of just a couple of minutes to significantly increase the driving range of the vehicle.

The key to the new Li-ion battery is the replacement of graphite at the anode with nanotubes synthesized from titanium dioxide. This is a departure from a lot of recent work toward improved anodes; other research teams have been using nanostructured silicon in place of graphite.

“With our nanotechnology, electric cars would be able to increase their range dramatically with just five minutes of charging, which is on par with the time needed to pump petrol for current cars,” said Chen Xiaodong, an associate professor at NTU Singapore, in a press release.

The new nanotube material, which is described in the journal Advanced Materials, is produced relatively easily, according to the researchers, by taking titanium dioxide nanoparticles and mixing them with sodium hydroxide. The real key to getting the long titanium dioxide nanotubes the nanoparticles yield is conducting the stirring process at the right temperature.

The technology has been patented and has been licensed by a company that says it could get a new generation of fast-charging batteries to market in two years.

While battery life and recharging have been significantly improved with the new battery design, it’s not clear that new batteries have a longer charge life, or what is known as gravimetric energy density (the amount of energy stored per unit mass). Instead, they have improved Li-ion’s relatively weak gravimetric power density (the maximum amount of power that can be supplied per unit mass) by eliminating the additives that are used to bind the electrodes to the anode. This allows the battery to transfer electrons and ions in and out of the battery more quickly. This translates into batteries that will last about the same amount of time on a charge as today’s current batteries, but can be charged up to near maximum very quickly.

NTU professor Rachid Yazami, who was the co-inventor of the lithium-graphite anode 34 years ago but not involved in this most recent research, has noted the significant improvement to Li-ion batteries this work represents.

Yazami said: “There is still room for improvement and one such key area is the power density—how much power can be stored in a certain amount of space—which directly relates to the fast charge ability. Ideally, the charge time for batteries in electric vehicles should be less than 15 minutes, which Prof Chen’s nanostructured anode has proven to do.”

Reusable carbon nanotubes could be the water filter of the future, says RIT study


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A new class of carbon nanotubes could be the next-generation clean-up crew for toxic sludge and contaminated water, say researchers at Rochester Institute of Technology.

Enhanced single-walled carbon nanotubes offer a more effective and sustainable approach to water treatment and remediation than the standard industry materials–silicon gels and activated carbon–according to a paper published in the March issue of Environmental Science Water: Research and Technology.

RIT researchers John-David Rocha and Reginald Rogers, authors of the study, demonstrate the potential of this emerging technology to clean polluted water. Their work applies carbon nanotubes to environmental problems in a specific new way that builds on a nearly two decades of nanomaterial research. Nanotubes are more commonly associated with fuel-cell research.

Graphene Mem 050815 3-anewapproachAlso Read About: UC BERKELEY: NANOTECHNOLOGY CAN HELP DELIVER AFFORDABLE, CLEAN WATER WITH GRAPHENE MEMBRANE: VIDEO

 

 

“This aspect is new–taking knowledge of carbon nanotubes and their properties and realizing, with new processing and characterization techniques, the advantages nanotubes can provide for removing contaminants for water,” said Rocha, assistant professor in the School of Chemistry and Materials Science in RIT’s College of Science.

Rocha and Rogers are advancing nanotube technology for environmental remediation and water filtration for home use.

“We have shown that we can regenerate these materials,” said Rogers, assistant professor of chemical engineering in RIT’s Kate Gleason College of Engineering. “In the future, when your water filter finally gets saturated, put it in the microwave for about five minutes and the impurities will get evaporated off.”

Carbon nanotubes are storage units measuring about 50,000 times smaller than the width of a human hair. Carbon reduced to the nanoscale defies the rules of physics and operates in a world of quantum mechanics in which small materials become mighty.

“We know carbon as graphite for our pencils, as diamonds, as soot,” Rocha said. “We can transform that soot or graphite into a nanometer-type material known as graphene.”

A single-walled carbon nanotube is created when a sheet of graphene is rolled up. The physical change alters the material’s chemical structure and determines how it behaves. The result is “one of the most heat conductive and electrically conductive materials in the world,” Rocha said. “These are properties that only come into play because they are at the nanometer scale.”

The RIT researchers created new techniques for manipulating the tiny materials. Rocha developed a method for isolating high-quality, single-walled carbon nanotubes and for sorting them according to their semiconductive or metallic properties. Rogers redistributed the pure carbon nanotubes into thin papers akin to carbon-copy paper.

“Once the papers are formed, now we have the adsorbent–what we use to pull the contaminants out of water,” Rogers said.

The filtration process works because “carbon nanotubes dislike water,” he added. Only the organic contaminants in the water stick to the nanotube, not the water molecules.

“This type of application has not been done before,” Rogers said. “Nanotubes used in this respect is new.”

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Co-authors on the paper are Ryan Capasse, RIT chemistry alumnus, and Anthony Dichiara, a former RIT post-doctoral researcher in chemical engineering now at the University of Washington.