Rice Universitiy’s James Tour Creates “Graphene NanoRibbons” for ‘NG Tank Applications’ .. Even Food and Beverage Packaging


Rice University mix of graphene nanoribbons, polymer has potential for cars, soda, beer 

Nanotubes imagesHOUSTON – (Oct. 10, 2013) – A discovery at Rice University aims to make vehicles that run on compressed natural gas more practical. It might also prolong the shelf life of bottled beer and soda.

The Rice lab of chemist James Tour has enhanced a polymer material to make it far more impermeable to pressurized gas and far lighter than the metal in tanks now used to contain the gas.

The combination could be a boon for an auto industry under pressure to market consumer cars that use cheaper natural gas. It could also find a market in food and beverage packaging.

Tour and his colleagues at Rice and in Hungary, Slovenia and India reported their results this week in the online edition of the American Chemistry Society journal ACS Nano.

By adding modified, single-atom-thick graphene nanoribbons (GNRs) to thermoplastic polyurethane (TPU), the Rice lab made it 1,000 times harder for gas molecules to escape, Tour said. That’s due to the ribbons’ even dispersion through the material. Because gas molecules cannot penetrate GNRs, they are faced with a “tortuous path” to freedom, he said.

The researchers acknowledged that a solid, two-dimensional sheet of graphene might be the perfect barrier to gas, but the production of graphene in such bulk quantities is not yet practical, Tour said.

But graphene nanoribbons are already there. Tour’s breakthrough “unzipping” technique for turning multiwalled carbon nanotubes into GNRs, first revealed in Nature in 2009, has been licensed for industrial production. “These are being produced in bulk, which should also make containers cheaper,” he said.

The researchers led by Rice graduate student Changsheng Xiang produced thin films of the composite material by solution casting GNRs treated with hexadecane and TPU, a block copolymer of polyurethane that combines hard and soft materials. The tiny amount of treated GNRs accounted for no more than 0.5 percent of the composite’s weight. But the overlapping 200- to 300-nanometer-wide ribbons dispersed so well that they were nearly as effective as large-sheet graphene in containing gas molecules. The GNRs’ geometry makes them far better than graphene sheets for processing into composites, Tour said.

They tested GNR/TPU films by putting pressurized nitrogen on one side and a vacuum on the other side. For films with no GNRs, the pressure dropped to zero in about 100 seconds as nitrogen escaped into the vacuum chamber. With GNRs at 0.5 percent, the pressure didn’t budge over 1,000 seconds, and it dropped only slightly over more than 18 hours.

Stress and strain tests also found that the 0.5 percent ratio was optimal for enhancing the polymer’s strength.

“The idea is to increase the toughness of the tank and make it impermeable to gas,” Tour said. “This becomes increasingly important as automakers think about powering cars with natural gas. Metal tanks that can handle natural gas under pressure are often much heavier than the automakers would like.”

He said the material could help to solve long-standing problems in food packaging, too.

“Remember when you were a kid, you’d get a balloon and it would be wilted the next day? That’s because gas molecules go through rubber or plastic,” Tour said. “It took years for scientists to figure out how to make a plastic bottle for soda. Once, you couldn’t get a carbonated drink in anything but a glass bottle, until they figured out how to modify plastic to contain the carbon dioxide bubbles. And even now, bottled soda goes flat after a period of months.

“Beer has a bigger problem and, in some ways, it’s the reverse problem,” he said. “Oxygen molecules get in through plastic and make the beer go bad.” Bottles that are effectively impermeable could lead to brew that stays fresh on the shelf for far longer, Tour said.

Co-authors of the paper are Rice graduate students Daniel Hashim, Zheng Yan, Zhiwei Peng, Chih-Chau Hwang, Gedeng Ruan and Errol Samuel; Rice alumnus Paris Cox; Bostjan Genorio, a former postdoctoral researcher at Rice and now an assistant professor at the University of Ljubljana, Slovenia; Akos Kukovecz, an associate professor of chemistry, and Zóltan Kónya, a researcher, both at the University of Szeged, Hungary; Parambath Sudeep, a research scholar at Cochin University of Science and Technology, India; Rice senior faculty fellow Robert Vajtai; and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry at Rice. Tour is the T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science at Rice.

The Air Force Research Laboratory through the University Technology Corp., the Office of Naval Research MURI graphene program and the Air Force Office of Scientific Research MURI program supported the research.

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Read the abstract at http://pubs.acs.org/doi/abs/10.1021/nn404843n

Follow Rice News and Media Relations via Twitter @RiceUNews

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Hybrid ribbons a gift for powerful batteries: Vanadium oxide – graphene material works well for lithium-ion storage


hybridribbon

Hybrid ribbons a gift for powerful batteries: Vanadium oxide – graphene material works well for lithium-ion storage

QDOTS imagesCAKXSY1K 8The Rice University lab of materials scientist Pulickel Ajayan determined that the well-studied material is a superior cathode for batteries that could supply both high energy density and significant power density. The research appears online this month in the American Chemical Society journal Nano Letters. The ribbons created at Rice are thousands of times thinner than a sheet of paper, yet have potential that far outweighs current materials for their ability to charge and discharge very quickly. Cathodes built into half-cells for testing at Rice fully charged and discharged in 20 seconds and retained more than 90 percent of their initial capacity after more than 1,000 cycles. “This is the direction battery research is going, not only for something with high energy density but also high power density,” Ajayan said. “It’s somewhere between a battery and a supercapacitor.”

1-hybridribbon

Hydrothermal processing of vanadium pentoxide and graphene oxide creates graphene-coated ribbons of crystalline vanadium oxide, which show great potential as ultrafast charging and discharging electrodes for lithium-ion batteries. Credit: Ajayan Group/Rice University

The ribbons also have the advantage of using relatively abundant and cheap materials. “This is done through a very simple hydrothermal process, and I think it would be easily scalable to large quantities,” he said. Ajayan said vanadium oxide has long been considered a material with great potential, and in fact vanadium pentoxide has been used in lithium-ion batteries for its special structure and high capacity.

But oxides are slow to charge and discharge, due to their low electrical conductivity. The high-conductivity graphene lattice that is literally baked in solves that problem nicely, he said, by serving as a speedy conduit for electrons and channels for ions.

The atom-thin graphene sheets bound to the crystals take up very little bulk. In the best samples made at Rice, fully 84 percent of the cathode’s weight was the lithium-slurping VO2, which held 204 milliamp hours of energy per gram. The researchers, led by Rice graduate student Yongji Gong and lead author Shubin Yang, said they believe that to be among the best overall performance ever seen for lithium-ion battery electrodes. “One challenge to production was controlling the conditions for the co-synthesis of VO2 ribbons with graphene,” Yang said.

The process involved suspending graphene oxide nanosheets with powdered vanadium pentoxide (layered vanadium oxide, with two atoms of vanadium and five of oxygen) in water and heating it in an autoclave for hours. The vanadium pentoxide was completely reduced to VO2, which crystallized into ribbons, while the graphene oxide was reduced to graphene, Yang said.

The ribbons, with a web-like coating of graphene, were only about 10 nanometers thick, up to 600 nanometers wide and tens of micrometers in length. “These ribbons were the building blocks of the three-dimensional architecture,” Yang said. “This unique structure was favorable for the ultrafast diffusion of both lithium ions and electrons during charge and discharge processes. It was the key to the achievement of excellent electrochemical performance.”

In testing the new material, Yang and Gong found its capacity for lithium storage remained stable after 200 cycles even at high temperatures (167 degrees Fahrenheit) at which other cathodes commonly decay, even at low charge-discharge rates. “We think this is real progress in the development of cathode materials for high-power lithium-ion batteries,” Ajayan said, suggesting the ribbons’ ability to be dispersed in a solvent might make them suitable as a component in the paintable batteries developed in his lab.

More information: pubs.acs.org/doi/abs/10.1021/nl400001u

Journal reference: Nano Letters

Graphene quantum dots: The next big small thing


QDOTS imagesCAKXSY1K 8Rice University-led team creates tiny materials in bulk from carbon fiber

 

 

This transmission electron microscope image shows a graphene quantum dot with zigzag edges. The quantum dots can be created in bulk from carbon fiber through a chemical process discovered at Rice University.0113_QUANTUM_HRTEM

A Rice University laboratory has found a way to turn common carbon fiber into graphene quantum dots, tiny specks of matter with properties expected to prove useful in electronic, optical and biomedical applications.

The Rice lab of materials scientist Pulickel Ajayan, in collaboration with colleagues in China, India, Japan and the Texas Medical Center, discovered a one-step chemical process that is markedly simpler than established techniques for making graphene quantum dots. The results were published online this month in the American Chemical Society’s journal Nano Letters.

“There have been several attempts to make graphene-based quantum dots with specific electronic and luminescent properties using chemical breakdown or e-beam lithography of graphene layers,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and of chemistry. “We thought that as these nanodomains of graphitized carbons already exist in carbon fibers, which are cheap and plenty, why not use them as the precursor?”

Quantum dots, discovered in the 1980s, are semiconductors that contain a size- and shape-dependent band gap. These have been promising structures for applications that range from computers, LEDs, solar cells and lasers to medical imaging devices. The sub-5 nanometer carbon-based quantum dots produced in bulk through the wet chemical process discovered at Rice are highly soluble, and their size can be controlled via the temperature at which they’re created.

The Rice researchers were attempting another experiment when they came across the technique. “We tried to selectively oxidize carbon fiber, and we found that was really hard,” said Wei Gao, a Rice graduate student who worked on the project with lead author Juan Peng, a visiting student from

Green-fluorescing graphene quantum dots created at Rice University surround a blue-stained nucleus in a human breast cancer cell. Cells were placed in a solution with the quantum dots for four hours. The dots, each smaller than 5 nanometers, easily passed through the cell membranes, showing their potential value for bio-imaging.

Nanjing University who studied in Ajayan’s lab last year. “We ended up with a solution and decided to look at a few drops with a transmission electron microscope.”

The specks they saw were bits of graphene or, more precisely, oxidized nanodomains of graphene extracted via chemical treatment of carbon fiber. “That was a complete surprise,” Gao said. “We call them quantum dots, but they’re two-dimensional, so what we really have here are graphene quantum discs.”

Gao said other techniques are expensive and take weeks to make small batches of graphene quantum dots. “Our starting material is cheap, commercially available carbon fiber. In a one-step treatment, we get a large amount of quantum dots. I think that’s the biggest advantage of our work,” she said.Further experimentation revealed interesting bits of information: The size of the dots, and thus their photoluminescent properties, could be controlled through processing at relatively low temperatures, from 80 to 120 degrees Celsius. “At 120, 100 and 80 degrees, we got blue, green and yellow luminescing dots,” she said.

They also found the dots’ edges tended to prefer the form known as zigzag. The edge of a sheet of graphene — the single-atom-thick form of carbon — determines its electrical characteristics, and zigzags are semiconducting.

Their luminescent properties give graphene quantum dots potential for imaging, protein analysis, cell tracking and other biomedical applications, Gao said. Tests at Houston’s MD Anderson Cancer Center and Baylor College of Medicine on two human breast cancer lines showed the dots easily found their way into the cytoplasm and did not interfere with the cells’ proliferation.

“The green quantum dots yielded a very good image,” said co-author Rebeca Romero Aburto, a graduate student in the Ajayan lab who also studies at MD Anderson. “The advantage of graphene dots over fluorophores is that their fluorescence is more stable and they don’t photobleach. They don’t lose their fluorescence as easily. They have a depth limit, so they may be good for in vitro and in vivo (small animal) studies, but perhaps not optimal for deep tissues in humans.

Dark spots on a transmission electron microscope grid are graphene quantum dots made through a wet chemical process at Rice University. The inset is a close-up of one dot. Graphene quantum dots may find use in electronic, optical and biomedical applications.

“But everything has to start in the lab, and these could be an interesting approach to further explore for bioimaging,” Romero Alburto said. “In the future, these graphene quantum dots could have high impact because they can be conjugated with other entities for sensing applications, too.”

Co-authors include Angel Martí, a professor of chemistry and bioengineering, postdoctoral research associates Zheng Liu and Liehui Ge, senior research scientist Lawrence Alemany and graduate student Xiaobo Zhan, all of Rice; Rice alumnus Li Song of Shinshu University, Japan; Bipin Kumar Gupta of the National Physical Laboratory, New Delhi, who worked at the Ajayan lab on an Indo-US Science and Technology Forum fellowship; Guanhui Gao of the Ocean University of China; Sajna Antony Vithayathil, a research technician, and Benny Abraham Kaipparettu, a postdoctoral researcher, both at Baylor College of Medicine; Takuya Hayashi, an associate professor of engineering at Shinshu University, Japan; and Jun-Jie Zhu, a professor of chemistry at Nanjing University.

The research was supported by Nanoholdings, the Office of Naval Research MURI program on graphene, the Natural Science Foundation of China, the National Basic Research Program of China, the Indo-US Science and Technology Forum and the Welch Foundation.

Light might prompt graphene devices on demand


MIKE WILLIAMS

 – OCTOBER 10, 2012

Rice University researchers find plasmonics show promise for optically induced electronics

Rice University researchers are doping graphene with light in a way that could lead to the more efficient design and manufacture of electronics, as well as novel security and cryptography devices.

Graphene circuitry

Nanoscale plasmonic antennas called nonamers placed on graphene have the potential to create electronic circuits by hitting them with light at particular frequencies, according to researchers at Rice University. The positively and negatively doped graphene can be prompted to form phantom circuits on demand.

Manufacturers chemically dope silicon to adjust its semiconducting properties. But the breakthrough reported in the American Chemical Society journal ACS Nano details a novel concept: plasmon-induced doping of graphene, the ultrastrong, highly conductive, single-atom-thick form of carbon.

That could facilitate the instant creation of circuitry – optically induced electronics – on graphene patterned with plasmonic antennas that can manipulate light and inject electrons into the material to affect its conductivity.

The research incorporates both theoretical and experimental work to show the potential for making simple, graphene-based diodes and transistors on demand. The work was done by Rice scientists Naomi Halas, Stanley C. Moore Professor in Electrical and Computer Engineering, a professor of biomedical engineering, chemistry, physics and astronomy and director of the Laboratory for Nanophotonics; and Peter Nordlander, professor of physics and astronomy and of electrical and computer engineering; physicist Frank Koppens of the Institute of Photonic Sciences in Barcelona, Spain; lead author Zheyu Fang, a postdoctoral researcher at Rice; and their colleagues.

“One of the major justifications for graphene research has always been about the electronics,” Nordlander said. “People who know silicon understand that electronics are only possible because it can be p- and n-doped (positive and negative), and we’re learning how this can be done on graphene.

“The doping of graphene is a key parameter in the development of graphene electronics,” he said. “You can’t buy graphene-based electronic devices now, but there’s no question that manufacturers are putting a lot of effort into it because of its potential high speed.”

Researchers have investigated many strategies for doping graphene, including attaching organic or metallic molecules to its hexagonal lattice. Making it selectively – and reversibly – amenable to doping would be like having a graphene blackboard upon which circuitry can be written and erased at will, depending on the colors, angles or polarization of the light hitting it.

Nonamers

Nonamers in the drawings at top and in the photos at bottom are arrays of nine gold nanoparticles deposited on graphene and tuned to particular frequencies of light. When illuminated, the plasmonic particles pump electrons into the graphene, according to researchers at Rice University who say the technology may lead to the creation of on-demand circuitry for electronic devices.

The ability to attach plasmonic nanoantennas to graphene affords just such a possibility. Halas and Nordlander have considerable expertise in the manipulation of the quasiparticles known as plasmons, which can be prompted to oscillate on the surface of a metal. In earlier work, they succeeded in depositing plasmonic nanoparticles that act as photodetectors on graphene.

These metal particles don’t so much reflect light as redirect its energy; the plasmons that flow in waves across the surface when excited emit light or can create “hot electrons” at particular, controllable wavelengths. Adjacent plasmonic particles can interact with each other in ways that are also tunable.

That effect can easily be seen in graphs of the material’s Fano resonance, where the plasmonic antennas called nonamers, each a little more than 300 nanometers across, clearly scatter light from a laser source except at the specific wavelength to which the antennas are tuned. For the Rice experiment, those nonamers – eight nanoscale gold discs arrayed around one larger disc – were deposited onto a sheet of graphene through electron-beam lithography. The nonamers were tuned to scatter light between 500 and 1,250 nanometers, but with destructive interference at about 825 nanometers.

At the point of destructive interference, most of the incident light energy is converted into hot electrons that transfer directly to the graphene sheet and change portions of the sheet from a conductor to an n-doped semiconductor.

Arrays of antennas can be affected in various ways and allow phantom circuits to materialize under the influence of light. “Quantum dot and plasmonic nanoparticle antennas can be tuned to respond to pretty much any color in the visible spectrum,” Nordlander said. “We can even tune them to different polarization states, or the shape of a wavefront.

“That’s the magic of plasmonics,” he said. “We can tune the plasmon resonance any way we want. In this case, we decided to do it at 825 nanometers because that is in the middle of the spectral range of our available light sources. We wanted to know that we could send light at different colors and see no effect, and at that particular color see a big effect.”

Nordlander said he foresees a day when, instead of using a key, people might wave a flashlight in a particular pattern to open a door by inducing the circuitry of a lock on demand. “Opening a lock becomes a direct event because we are sending the right lights toward the substrate and creating the integrated circuits. It will only answer to my call,” he said.

Rice co-authors of the paper are graduate students Yumin Wang and Andrea Schlather, research scientist Zheng Liu, and Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor in Mechanical Engineering and Materials Science and of chemistry.

The research was supported by the Robert A. Welch Foundation, the Office of Naval Research, the Department of Defense National Security Science and Engineering Faculty Fellows program and Fundacio Cellex Barcelona.