Nanotechnology Now

Our NanoNews Digest Sponsors


Heifer International

Wikipedia Affiliate Button

Home > Press > Molecules pass through nanotubes at size-dependent speeds

A diagram of one of the group's experimental setups shows a copper plate that can be heated using a torch underneath it, to study the effect of temperature on the process. On top of the plate, an apparatus consisting of two reservoirs separated by a silicon structure that has a single carbon nanotube on top of it. When a power source is connected to the electrodes (the wires extending up from the device), charged molecules (ions) from one of the reservoirs can pass through the tube, and its progress can be monitored using a scanning electron microscope.
Illustration courtesy of Choi et al.
A diagram of one of the group's experimental setups shows a copper plate that can be heated using a torch underneath it, to study the effect of temperature on the process. On top of the plate, an apparatus consisting of two reservoirs separated by a silicon structure that has a single carbon nanotube on top of it. When a power source is connected to the electrodes (the wires extending up from the device), charged molecules (ions) from one of the reservoirs can pass through the tube, and its progress can be monitored using a scanning electron microscope.

Illustration courtesy of Choi et al.

Abstract:
Like a pea going through a straw, tiny molecules can pass through microscopic cylinders known as nanotubes. This could potentially be used to select molecules according to size for example, to purify water by allowing water molecules to pass through while blocking salt or other substances.

Molecules pass through nanotubes at size-dependent speeds

Cambridge, MA | Posted on September 12th, 2013

Now, researchers at MIT, Seoul University in Korea and Ursinus College in Pennsylvania have found that such tubes are more selective than had been thought: Molecules of a precise size can zip through five times faster than those that are a bit smaller or larger. The new findings are published in the journal Nature Communications by MIT professor Michael Strano, graduate students Wonjoon Choi and Zachary Ulissi, and three others.

This size-dependence in nanotube transport was completely unexpected, says Strano, a professor of chemical engineering at MIT. "This work illustrates how transport in pores of this type remains exotic and relatively unexplored," he says.

The team "looked at ion transport through the smallest single nanopores that have been studied," Strano says. The carbon nanotubes they studied had widths ranging from 0.9 to 2 nanometers about the diameter of a DNA helix and were about 1 millimeter long.

"What we found was not predicted by theory," he says: Up to a certain diameter, the flow of ions through a nanotube increased steadily but then beyond that diameter, the flow decreased. "The dependence is a volcano-shaped plot," Strano says.

The peak flow, at the center of that plot, allows transport that is five times greater than transport at smaller or larger diameters. "The experimental results are counterintuitive," Strano says, "that there appears to be an optimal diameter."

This size-dependence of transport could turn out to be useful in a variety of technologies, he suggests, including proton-exchange membrane (PEM) fuel cells, where molecules of oxygen or hydrogen must pass through tiny pores in a membrane to produce electricity. Another potential application is in DNA-sequencing devices, where DNA segments typically hurtle through pores much too quickly to be analyzed. The new understanding may provide a method for "tuning" the transit speed to slow the DNA sequences enough for analysis.

The unexpected size-dependence results from two phenomena, Strano suggests. According to a theory developed by the team, there is first an attractive force, in which ions' electrical charge causes them to be pulled by an electric field through the pore. Since the ions and the tubes are all submerged in water, some water gets pulled along as well.

Up to a certain diameter, those water molecules form a layer, or a few layers, around the ion and are pulled along with it, the team theorizes. But as the opening gets bigger, the water behaves as a bulk material, slowing the ions' passage. "This explanation is consistent with our experimental observations and molecular simulations of water inside of nanotubes of this type," Strano says though he stresses that while the data on the ion flow is clear-cut, additional theoretical work is needed to fully understand this process.

The finding may help in designing better membranes for desalination of water. The biggest problem with today's membranes is the tradeoff between selectivity versus flow rates: Bigger pores let the water flow through faster, but are less selective. Nanotubes' nonlinear response may provide a way around that.

"The results suggest that by using nanopores of a specific diameter, it may be possible to achieve maximum selectivity with maximum throughput" by optimizing the pore size, Strano says.

The work could also lead to new sensors capable of detecting specific contaminants in water, the team says. For example, arsenic contamination of groundwater is a serious health concern in some regions, but there is no reliable way of testing arsenic concentrations in water. The selectivity of nanotubes might make it possible to design a simple detector that could measure such contamination, Strano says.

In addition to Choi and Ulissi, the work was carried out by MIT graduate students Steven Shimizu and Darin Bellisario, as well as Mark Ellison of Ursinus.

The work was supported by the U.S. Department of Energy and Department of Defense.

Written by David Chandler, MIT News Office

####

For more information, please click here

Contacts:
Sarah McDonnell

617-253-8923

Copyright © Massachusetts Institute of Technology

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related Links

Paper: "Diameter-dependent ion transport through the interior of isolated single-walled carbon nanotubes":

Related News Press

News and information

Pixel-array quantum cascade detector paves the way for portable thermal imaging devices: Research team from TU-Wien Center for Micro- and Nanostructures have developed a new 'cooler' sensing instrument thereby increasing energy-efficiency and enhancing mobility for diagnostic tes July 28th, 2016

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

Thomas Swan and NGI announce unique partnership July 28th, 2016

Penn team uses nanoparticles to break up plaque and prevent cavities July 28th, 2016

Govt.-Legislation/Regulation/Funding/Policy

Thomas Swan and NGI announce unique partnership July 28th, 2016

Penn team uses nanoparticles to break up plaque and prevent cavities July 28th, 2016

Beating the heat a challenge at the nanoscale: Rice University scientists detect thermal boundary that hinders ultracold experiments July 28th, 2016

Enhancing molecular imaging with light: New technology platform increases spectroscopic resolution by 4 fold July 27th, 2016

Nanotubes/Buckyballs/Fullerenes

Easier, faster, cheaper: A full-filling approach to making nanotubes of consistent quality: Approach opens a straightforward route for engineering the properties of single-wall carbon nanotubes July 19th, 2016

Sensing trouble: A new way to detect hidden damage in bridges, roads: University of Delaware engineers devise new method for monitoring structural health July 8th, 2016

Wireless, wearable toxic-gas detector: Inexpensive sensors could be worn by soldiers to detect hazardous chemical agents July 4th, 2016

Nanotubes' 'stuffing' as is: A scientist from the Lomonosov Moscow State University studied the types of carbon nanotubes' 'stuffing' June 2nd, 2016

Sensors

Ultrasensitive sensor using N-doped graphene July 26th, 2016

Integration of novel materials with silicon chips makes new 'smart' devices possible July 25th, 2016

Electron 'spin control' of levitated nanodiamonds could bring advances in sensors, quantum information processing July 20th, 2016

Easier, faster, cheaper: A full-filling approach to making nanotubes of consistent quality: Approach opens a straightforward route for engineering the properties of single-wall carbon nanotubes July 19th, 2016

Discoveries

Pixel-array quantum cascade detector paves the way for portable thermal imaging devices: Research team from TU-Wien Center for Micro- and Nanostructures have developed a new 'cooler' sensing instrument thereby increasing energy-efficiency and enhancing mobility for diagnostic tes July 28th, 2016

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

Penn team uses nanoparticles to break up plaque and prevent cavities July 28th, 2016

Beating the heat a challenge at the nanoscale: Rice University scientists detect thermal boundary that hinders ultracold experiments July 28th, 2016

Announcements

Pixel-array quantum cascade detector paves the way for portable thermal imaging devices: Research team from TU-Wien Center for Micro- and Nanostructures have developed a new 'cooler' sensing instrument thereby increasing energy-efficiency and enhancing mobility for diagnostic tes July 28th, 2016

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

Thomas Swan and NGI announce unique partnership July 28th, 2016

Penn team uses nanoparticles to break up plaque and prevent cavities July 28th, 2016

Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

Penn team uses nanoparticles to break up plaque and prevent cavities July 28th, 2016

Beating the heat a challenge at the nanoscale: Rice University scientists detect thermal boundary that hinders ultracold experiments July 28th, 2016

WSU researchers 'watch' crystal structure change in real time: Breakthrough made possible by new Argonne facility July 27th, 2016

Military

Beating the heat a challenge at the nanoscale: Rice University scientists detect thermal boundary that hinders ultracold experiments July 28th, 2016

Ultrasensitive sensor using N-doped graphene July 26th, 2016

Borrowing from pastry chefs, engineers create nanolayered composites: Method to stack hundreds of nanoscale layers could open new vistas in materials science July 25th, 2016

Integration of novel materials with silicon chips makes new 'smart' devices possible July 25th, 2016

Environment

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

A 'smart dress' for oil-degrading bacteria July 24th, 2016

News from Quorum: The College of New Jersey use the Quorum Cryo-SEM preparation system in a project to study ice crystals in high altitude clouds July 19th, 2016

Researchers improve catalyst efficiency for clean industries: Method reduces use of expensive platinum July 8th, 2016

Water

Dirty to drinkable: Engineers develop novel hybrid nanomaterials to transform water July 28th, 2016

New nontoxic process promises larger ultrathin sheets of 2-D nanomaterials July 27th, 2016

Electricity generated with water, salt and a 3-atoms-thick membrane: EPFL researchers have developed a system that generates electricity from osmosis with unparalleled efficiency. Their work, featured in Nature, uses seawater, fresh water, and a new type of membrane just 3 atoms July 15th, 2016

Bouncing droplets remove contaminants like pogo jumpers: Researchers at Duke University and the University of British Columbia are exploring whether surfaces can shed dirt without being subjected to fragile coatings July 7th, 2016

NanoNews-Digest
The latest news from around the world, FREE




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoTech-Transfer
University Technology Transfer & Patents
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project







Car Brands
Buy website traffic