Researchers clarify properties of 'confined' water within single-walled carbon nanotube pores

 

This global temperature-diameter (T-D) phase diagram of water inside SWCNTs shows that, depending on the water content, hollow or filled ice will form. On the right, hollow- and filled-ice nanotubes can be calculated at low temperature for SWCNTs with diameters indicated with (a) and (b) in the lower portion of the phase diagram. Credit: Yutaka Maniwa

Water and ice may not be among the first things that come to mind when you think about single-walled carbon nanotubes (SWCNTs), but a Japan-based research team hoping to get a clearer understanding of the phase behavior of confined water in the cylindrical pores of carbon nanotubes zeroed in on confined water's properties and made some surprising discoveries.

The team, from Tokyo Metropolitan University, Nagoya University, Japan Science and Technology Agency, and National Institute of Advanced Industrial Science and Technology, describes their findings in the American Institute of Physics' Journal of Chemical Physics.Although carbo nanotubes consist of hydrophobic (water repelling) graphene sheets, experimental studies on SWCNTs show that water can indeed be confined in open-ended carbon nanotubes.

This discovery gives us a deeper understanding of the properties of nanoconfined water within the pores of SWCNTs, which is a key to the future of nanoscience. It's anticipated that nanoconfined water within carbon nanotubes can open the door to the development of a variety of nifty new nanothings?nanofiltration systems, molecular nanovalves, molecular water pumps, nanoscale power cells, and even nanoscale ferroelectric devices.

"When materials are confined at the atomic scale they exhibit unusual properties not otherwise observed, due to the so-called 'nanoconfinement effect.' In geology, for example, nanoconfined water provides the driving force for frost heaves in soil, and also for the swelling of clay minerals," explains Yutaka Maniwa, a professor in the Department of Physics at Tokyo Metropolitan University. "We experimentally studied this type of effect for water using SWCNTs."

Water within SWCNTs in the range of 1.68 to 2.40 nanometers undergoes a wet-dry type of transition when temperature is decreased. And the team discovered that when SWCNTs are extremely narrow, the water inside forms tubule ices that are quite different from any bulk ices known so far. Strikingly, their melting point rises as the SWCNT diameter decreases?contrary to that of bulk water inside a large-diameter capillary. In fact, tubule ice occurred even at room temperature inside SWCNTs.

"We extended our studies to the larger diameter SWCNTs up to 2.40 nanometers and successfully proposed a global phase behavior of water," says Maniwa. "This phase diagram (See Figure) covers a crossover from microscopic to macroscopic regions. In the macroscopic region, a novel wet-dry transition was newly explored at low temperature."

Results such as these contribute to a greater understanding of fundamental science because nanoconfined water exists and plays a vital role everywhere on Earth?including our bodies. "Understanding the nanoconfined effect on the properties of materials is also crucial to develop new devices, such as proton-conducting membranes and nanofiltration," Maniwa notes.

Next up, the team plans to investigate the physical properties of confined water discovered so far inside SWCNTs (such as dielectricity and proton conduction). They will pursue this to obtain a better understanding of the molecular structure and transport properties in biological systems.

Provided by American Institute of Physics

New carbon nanotube sensor can detect tiny traces of explosives

The MIT researchers' sensor uses carbon nanotubes (in yellow) covered in protein fragments to detect even a single molecule of an explosive, such as the TNT molecule shown here.

MIT researchers have created a new detector so sensitive it can pick up a single molecule of an explosive such as TNT.

To create the sensors, chemical engineers led by Michael Strano coated carbon nanotubes ? hollow, one-atom-thick cylinders made of pure carbon ? with protein fragments normally found in bee venom. This is the first time those proteins have been shown to react to explosives, specifically a class known as nitro-aromatic compounds that includes TNT.

If developed into commercial devices, such sensors would be far more sensitive than existing explosives detectors ? commonly used at airports, for example ? which use spectrometry to analyze charged particles as they move through the air.

"Ion mobility spectrometers are widely deployed because they are inexpensive and very reliable. However, this next generation of nanosensors can improve upon this by having the ultimate detection limit, [detecting] single molecules of explosives at room temperature and atmospheric pressure," says Strano, the Charles (1951) and Hilda Roddey Career Development Associate Professor of Chemical Engineering.

A former graduate student in Strano's lab, Daniel Heller (now a Damon Runyon Fellow at MIT's David H. Koch Institute for Integrative Cancer Research), is lead author of a paper describing the technology in the Proceedings of the National Academy of Sciences. The paper appears online this week.

Strano has filed for a patent on the technology, which makes use of protein fragments called bombolitins. "Scientists have studied these peptides, but as far as we know, they've never been shown to have an affinity for and recognize explosive molecules in any way," he says.

In recent years, Strano's lab has developed carbon-nanotube sensors for a variety of molecules, including nitric oxide, hydrogen peroxide and toxic agents such as the nerve gas sarin. Such sensors take advantage of carbon nanotubes' natural fluorescence, by coupling them to a molecule that binds to a specific target. When the target is bound, the tubes' fluorescence brightens or dims.

The new explosives sensor works in a slightly different way. When the target binds to the bee-venom proteins coating the nanotubes, it shifts the fluorescent light's wavelength, instead of changing its intensity. The researchers built a new type of microscope to read the signal, which can't be seen with the naked eye. This type of sensor, the first of its kind, is easier to work with because it is not influenced by ambient light.

"For a fluorescent sensor, using the intensity of the fluorescent light to read the signal is more error-prone and noisier than measuring a wavelength," Strano says.

Each nanotube-peptide combination reacts differently to different nitro-aromatic compounds. By using several different nanotubes coated in different bombolitins, the researchers can identify a unique "fingerprint" for each explosive they might want to detect. The nanotubes can also sense the breakdown products of such explosives.

"Compounds such as TNT decompose in the environment, creating other molecule types, and those derivatives could also be identified with this type of sensor," Strano says. "Because molecules in the environment are constantly changing into other chemicals, we need sensor platforms that can detect the entire network and classes of chemicals, instead of just one type."

The researchers also showed that the nanotubes can detect two pesticides that are nitro-aromatic compounds as well, making them potentially useful as environmental sensors. The research was funded by the Institute for Soldier Nanotechnologies at MIT.

Philip Collins, a professor of physics at the University of California at Irvine, says the new approach is a novel extension of Strano's previous work on carbon-nanotube sensors. "It's nice what they've done ? combined a couple of different things that are not sensitive to explosives, and shown that the combination is sensitive," says Collins, who was not involved in this research.

The technology has already drawn commercial and military interest, Strano says. For the sensor to become practical for widespread use, it would have to be coupled with a commercially available concentrator that would bring any molecules floating in the air in contact with the carbon nanotubes.

"It doesn't mean that we are ready to put these onto a subway and detect explosives immediately. But it does mean that now the sensor itself is no longer the bottleneck," Strano says. "If there's one molecule in a sample, and if you can get it to the sensor, you can now detect and quantify it."

NEC's 'Earth simulator' succeeds in prediction of photochemical reactions inside carbon nanotubes

NEC's 'Earth simulator' succeeds in prediction of photochemical reactions inside carbon nanotubes

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Dissociation of hydrogen chloride (HCI) molecule trapped inside a carbon nanotube due to the laser pulse irradiation.

NEC Corporation announced today that it succeeded in the world's first simulation-based prediction of laser-induced photochemical reactions that can efficiently eject a hydrogen atom from a hydrogen chloride molecule trapped inside a carbon nanotube. The simulation was conducted on the "Earth Simulator," which NEC deployed for the Japan Agency for Marine-Earth Science and Technology, an independent administrative organization.

These results are expected to pave the way for the quantity synthesis of not only hydrogen, but also inexpensive materials through the facilitation of known photochemical reactions due to the laser pulse irradiation, as well as the development of new materials.

Results were published online on December 7 by the Physical Review Letters, a prestigious academic journal of the American Institute of Physics.

The Earth Simulator topped the HPC Challenge Award for Fast Fourier Transform (FFT) performance at the SC10 supercomputing conference held in the United States in November 2010. The Earth Simulator demonstrated the world's top-level computing efficiency, especially for complicated applications, including nanoscience, quest for new materials and weather prediction.

The FFT dominates almost half of the processing in the application software used for this research. The Earth Simulator significantly reduced the computing time needed for laser pulse irradiation; taking just two days in contrast to the several months required by conventional supercomputers. As a result, it is now possible to determine the optimum laser intensity in a realistic timeframe with a series of simulations for variable laser intensities.

This research was carried out under a collaborative research contract with JAMSTEC titled "Large-scale Simulation of Characteristics of Carbon Nanotubes."

The application fields of the Earth Simulator, with its outstanding sustained performance, span a wide range of areas. For example, it contributes to more accurate climate change projections and the comprehensive understanding of environmental issues, such as the assessment of the effects of global warming for the fifth report of the Intergovernmental Panel on Climate Change (IPCC), as well as prevention and mitigation of natural disasters through high-resolution simulations of earthquakes and seismic surges. Moreover, the Earth Simulator is utilized heavily in tackling energy issues and developing new materials by leveraging cooperative relations with industry partners.

Looking forward, NEC aims to support leading-edge research and development capitalizing on advanced supercomputers, such as the Earth Simulator, with superior HPC technologies.

NEC's 'Earth simulator' succeeds in prediction of photochemical reactions inside carbon nanotubes

NEC's 'Earth simulator' succeeds in prediction of photochemical reactions inside carbon nanotubes

Enlarge

Dissociation of hydrogen chloride (HCI) molecule trapped inside a carbon nanotube due to the laser pulse irradiation.

NEC Corporation announced today that it succeeded in the world's first simulation-based prediction of laser-induced photochemical reactions that can efficiently eject a hydrogen atom from a hydrogen chloride molecule trapped inside a carbon nanotube. The simulation was conducted on the "Earth Simulator," which NEC deployed for the Japan Agency for Marine-Earth Science and Technology, an independent administrative organization.

These results are expected to pave the way for the quantity synthesis of not only hydrogen, but also inexpensive materials through the facilitation of known photochemical reactions due to the laser pulse irradiation, as well as the development of new materials.

Results were published online on December 7 by the Physical Review Letters, a prestigious academic journal of the American Institute of Physics.

The Earth Simulator topped the HPC Challenge Award for Fast Fourier Transform (FFT) performance at the SC10 supercomputing conference held in the United States in November 2010. The Earth Simulator demonstrated the world's top-level computing efficiency, especially for complicated applications, including nanoscience, quest for new materials and weather prediction.

The FFT dominates almost half of the processing in the application software used for this research. The Earth Simulator significantly reduced the computing time needed for laser pulse irradiation; taking just two days in contrast to the several months required by conventional supercomputers. As a result, it is now possible to determine the optimum laser intensity in a realistic timeframe with a series of simulations for variable laser intensities.

This research was carried out under a collaborative research contract with JAMSTEC titled "Large-scale Simulation of Characteristics of Carbon Nanotubes."

The application fields of the Earth Simulator, with its outstanding sustained performance, span a wide range of areas. For example, it contributes to more accurate climate change projections and the comprehensive understanding of environmental issues, such as the assessment of the effects of global warming for the fifth report of the Intergovernmental Panel on Climate Change (IPCC), as well as prevention and mitigation of natural disasters through high-resolution simulations of earthquakes and seismic surges. Moreover, the Earth Simulator is utilized heavily in tackling energy issues and developing new materials by leveraging cooperative relations with industry partners.

Looking forward, NEC aims to support leading-edge research and development capitalizing on advanced supercomputers, such as the Earth Simulator, with superior HPC technologies.

'Molecular torch' between carbon nanotubes emits electroluminescence

'Molecular torch' between carbon nanotubes emits electroluminescence

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For the first time, scientists observed electroluminescence from a molecule lodged in a gap between carbon nanotubes. Image credit: Karlsruhe Institute of Technology.

(PhysOrg.com) -- A single molecule bridging a "broken" single-walled carbon nanotube (CNT) is barely visible through a powerful scanning electron microscope, but the precisely assembled system can act as a functional solid-state electronics device. These CNT-molecule-CNT junctions have been developed only in the past few years, and measuring their optical characteristics has been a difficult task. In a new study, scientists have observed for the first time that the molecule between the nanotubes can emit light due to an electric current passing through it, a phenomenon called electroluminescence.

In their study, scientists Christoph W. Marquardt from the Karlsruhe Institute of Technology in Karlsruhe, Germany, and coauthors from the University of Basel in Basel, Switzerland; the Poznan University of Economics in Poznan, Poland; and the DFG Center for Functional Nanostructures in Karlsruhe, Germany, have published their study in a recent issue of Nature Nanotechnology.

As the scientists explained, the carbon nanotubes contain a pair of metallic electrodes. Through electrical breakdown, the scientists could create a gap of just a few nanometers between the electrodes. The gap’s position and size of less than 10 nm had to be controlled with nanoscale precision in order to allow for a current. The researchers then assembled a molecule having a 6-nm-long rod-like structure and electrical characteristics that enabled it to be electrostatically trapped in the gap, completing the “circuit” between the electrodes. They predicted that the electrode gap could host no more than one to three of these molecules.

When applying a voltage to the electrodes, the scientists observed bright spots of electroluminescence, and they could control the electroluminescence by switching the voltage on and off. The scientists could determine that the light was coming from the molecule between the electrodes by overlaying an image captured previously with external illumination. The researchers observed a small bright spot between the electrodes in 6 of 20 CNT-molecule-CNT devices. They calculated that, on average, one photon was emitted per 1 billion electrons.

"This is the first time that electroluminescence has been observed from CNT-molecule-CNT junctions," coauthor Ralph Krupke from the Karlsruhe of Technology and DFG Center for Functional Nanostructures told PhysOrg.com. He noted that, in 2004, Dong, et al., observed electroluminescence from a molecule in a scanning tunneling microscope setup.

“In our view, the greatest significance is that we succeeded in forming a rigid solid-state device by integrating a bottom-up structure, the molecule, into a top-down structure, the CNT gap,” he said. “Thereby we had to control the critical dimensions and the molecule had to be tailored to enable light emission under voltage bias. Furthermore, from a molecular electronics point of view, it is the first time that the presence of the molecule in the gap is confirmed by its optical signature.”

Currently, the scientists are fabricating variations of this device by using different molecules that emit light at different wavelengths. The results of the study show that carbon nanotubes could have a variety of applications in molecular electronics.

"Molecular electronics aims at the fundamental understanding of charge transport through molecules and is motivated by the vision of molecular circuits to enable miniscule, powerful and energy-efficient computers,” Krupke said. “Our result is important for fundamental science but it also adds to the molecular electronics vision an optoelectronic component, i.e., the development of optoelectronic components on the basis of single molecules."