Nanotechnology Now





Heifer International

Wikipedia Affiliate Button


DHgate

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

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Haydale Named Lead Sponsor for Cambridge Graphene Festival May 22nd, 2015

Simulations predict flat liquid May 21st, 2015

Govt.-Legislation/Regulation/Funding/Policy

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

SUNY Poly CNSE and NIOSH Launch Federal Nano Health and Safety Consortium: May 20th, 2015

Nanotubes/Buckyballs/Fullerenes

Researchers develop new way to manufacture nanofibers May 21st, 2015

Sandia researchers first to measure thermoelectric behavior by 'Tinkertoy' materials May 20th, 2015

Cotton fibres instead of carbon nanotubes May 9th, 2015

A better way to build DNA scaffolds: McGill researchers devise new technique to produce long, custom-designed DNA strands May 6th, 2015

Sensors

Record high sensitive Graphene Hall sensors May 21st, 2015

Graphene enables tunable microwave antenna May 15th, 2015

Janusz Bryzek Joins MEMS Industry Group to Lead New TSensors Division - New Division will Focus on Accelerating Development of Emerging Ultra-high Volume Sensors Supporting Abundance, mHealth and IoT May 14th, 2015

Nano-policing pollution May 13th, 2015

Discoveries

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Turn that defect upside down: Twin boundaries in lithium-ion batteries May 21st, 2015

Announcements

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Haydale Named Lead Sponsor for Cambridge Graphene Festival May 22nd, 2015

INSIDDE: Uncovering the real history of art using a graphene scanner May 21st, 2015

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

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

Simulations predict flat liquid May 21st, 2015

Researchers develop new way to manufacture nanofibers May 21st, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Military

New Antibacterial Wound Dressing in Iran Can Display Replacement Time May 22nd, 2015

Nanotherapy effective in mice with multiple myeloma May 21st, 2015

Taking control of light emission: Researchers find a way of tuning light waves by pairing 2 exotic 2-D materials May 20th, 2015

Wearables may get boost from boron-infused graphene: Rice U. researchers flex muscle of laser-written microsupercapacitors May 18th, 2015

Environment

Conversion of Greenhouse Gases to Syngas in Presence of Nanocatalysts in Iran May 22nd, 2015

Directa Plus in Barcelona to present the innovative project GEnIuS for oil spills clean-up activities: The company has created a graphene-based product for the remediation of water contaminated by oil and hydrocarbons May 21st, 2015

Nano-policing pollution May 13th, 2015

Chemists strike nano-gold: 4 new atomic structures for gold nanoparticle clusters: Research builds upon work by Nobel Prize-winning team from Stanford University April 28th, 2015

Water

Nanosorbent Produced in Iran to Adsorb Tiny Amounts of Aromatic Hydrocarbon from Seawater May 18th, 2015

Iran Unveils New Home-Made Medicines, Nanotechnology Products May 14th, 2015

Plugging up leaky graphene: New technique may enable faster, more durable water filters May 7th, 2015

Production of Industrial Nano-Membrane for Water, Wastewater Purification Device in Iran May 2nd, 2015

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