Subscribe free to our newsletters via your
. 24/7 Space News .




CARBON WORLDS
NIST researchers propose new old way to purify carbon nanotubes
by Staff Writers
Washington DC (SPX) May 09, 2013


Shown are three examples of partitioning carbon nanotubes in liquid phases. Left: nanotubes partitioned by diameter. Smaller diameters, on the bottom, appear purple. Center: partitioned between semiconductors (amber, top) and metals. Right: A sample with different diameter range partitioned between metals (yellow) and semiconductors. Color differences are due to differences in electronic structure. Credit: Michael Baum, NIST.

An old, somewhat passe, trick used to purify protein samples based on their affinity for water has found new fans at the National Institute of Standards and Technology (NIST), where materials scientists are using it to divvy up solutions of carbon nanotubes, separating the metallic nanotubes from semiconductors.

They say it's a fast, easy and cheap way to produce high-purity samples of carbon nanotubes for use in nanoscale electronics and many other applications.*

Carbon nanotubes are formed from rolled-up sheets of carbon atoms arranged in a hexagonal pattern resembling chicken wire.

One of the amazing features of nanotubes is that, depending on just how the sheet rolls up, a quality called chirality, the resulting tube can behave either like a semiconductor, with various properties, or like a metal, with electrical conductance up to 10 times better than copper.

One big issue in creating commercially viable electronics based on nanotubes is being able to efficiently sort out the kind you want.

Thinking about how to do this, says NIST researcher Constantine Khripin, brought up the subject of biochemists and so-called "two-phase liquid extraction."

"Biologists used this to separate proteins, even viruses," says Khripin, "It's an old technique, it was popular in the 70s, but then HPLC [high-performance liquid chromatography] replaced a lot of those techniques."

People use HPLC to partition carbon nanotubes as well, he says, but it's less successful. HPLC divides things by exploiting differences in the mobility of the desired molecules as they travel small columns loaded with tiny spheres, but carbon nanotubes tend to stick to the spheres, reducing yield and eventually clogging the equipment.

The concept of liquid extraction is relatively straightforward. You make a mixture in water of two polymers that you've selected to be just slightly different in their "hydrophobicity," or tendency to mix with water. Add in your sample of stuff to be separated, stir vigorously and wait.

The polymer solutions will gradually separate into two distinct portions or "phases," the lighter one on top. And they'll bring along with them those molecules in your sample that share a similar degree of hydrophobicity.

It turns out that this works pretty well with nanotubes because of differences in their electronic structure-the semiconductor forms, for example, are more hydrophobic than the metallic forms. It's not perfect, of course, but a few sequential separations ends up with a sample where the undesired forms are essentially undetectable.

Be honest. It's not that easy. "No," agrees, Khripin, "People tried this before and it didn't work. The breakthrough was to realize that you need a very subtle difference between the two phases. The difference in hydrophobity between nanotubes is tiny, tiny, tiny." But you can engineer that with careful addition of salts and surfactants.

"This technique uses some vials and a bench-top centrifuge worth a couple hundred dollars, and it takes under a minute," observes team member Jeffrey Fagan.

"The other techniques people use require an HPLC on the order of $50,000 and the yields are relatively low, or an ultracentrifuge that takes 12 to 20 hours to separate out the different metals from semiconductors, and it's tricky and cumbersome."

"The nanotube metrology project at NIST has been around for a quite a number of years," says senior team member Ming Zheng.

"It has been a constant interest of ours to develop new ways to separate nanotubes, cheaper ways, that industry can use in the development of nanoelectronics and other applications. We really think we have a method here that fits all the criteria that people are looking for. It's easy, it's scalable, it's high resolution-all the good attributes put together."

* C.Y. Khripin , J.A. Fagan and M. Zheng. Spontaneous partition of carbon nanotubes in polymer-modified aqueous phases. J. Am. Chem. Soc., Article ASAP April 22, 2013 (web publication). DOI: 10.1021/ja402762e

.


Related Links
National Institute of Standards and Technology (NIST)
Carbon Worlds - where graphite, diamond, amorphous, fullerenes meet






Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle








CARBON WORLDS
Graphene's high-speed seesaw
Manchester, UK (SPX) May 03, 2013
Writing in Nature Communications, the researchers report the first graphene-based transistor with bistable characteristics, which means that the device can spontaneously switch between two electronic states. Such devices are in great demand as emitters of electromagnetic waves in the high-frequency range between radar and infra-red, relevant for applications such as security systems and medical ... read more


CARBON WORLDS
Northrop Grumman Completes Lunar Lander Study for Golden Spike Company

Scientists Use Laser to Find Soviet Moon Rover

Characterizing The Lunar Radiation Environment

Russia rekindles Moon exploration program, intends setting up first human outposts there

CARBON WORLDS
Buzz Aldrin says US must colonize Mars

Landing is key puzzle in Mars trip plans: experts

New analysis suggests wind, not water, formed mound on Mars

India to have five rocket launches, including Mars mission, in 2013

CARBON WORLDS
Outside View: Patents laws and suffering innovators

Glow-in-the-Dark Plants on the ISS

Russia Confirms Plans to Send Sarah Brightman to Space

Success Continues as NASA's Orion Parachute Tests Get More Difficult

CARBON WORLDS
China launches communications satellite

On Course for Shenzhou 10

Yuanwang III, VI depart for space-tracking missions

Shenzhou's Shadow Crew

CARBON WORLDS
The fourth Automated Transfer Vehicle is ready to meet up with its Ariane 5

NASA to pay Russia $424 mln more for lift into space

NASA Extends Crew Flight Contract with Russian Space Agency

Cargo spaceship docks with ISS despite antenna mishap

CARBON WORLDS
Angara Rocket Launch Delayed to 2014

ESA's Vega launcher scores new success with Proba-V

European Vega rocket launch delayed due to weather

First of Four Sounding Rockets Launched from the Marshall Islands

CARBON WORLDS
The Great Exoplanet Debate

NASA's Spitzer Puts Planets in a Petri Dish

Two New Exoplanets Detected with Kepler, SOPHIE and HARPS-N

Astronomer studies far-off worlds through 'characterization by proxy'

CARBON WORLDS
iGT Debuts Airborne Satcom Solutions for Secure Connectivity and Situational Awareness

UF launches HiPerGator, Florida's most powerful supercomputer

Electrolysis method described for making 'green' iron

Do-it-yourself invisibility with 3D printing




The content herein, unless otherwise known to be public domain, are Copyright 1995-2014 - Space Media Network. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA Portal Reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement,agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement