Nanotechnology Now

Our NanoNews Digest Sponsors
Heifer International



Home > Press > Plugging up leaky graphene: New technique may enable faster, more durable water filters

Abstract:
For faster, longer-lasting water filters, some scientists are looking to graphene —thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.

Plugging up leaky graphene: New technique may enable faster, more durable water filters

Cambridge, MA | Posted on May 7th, 2015

Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.

Now engineers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.

Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.

In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.

Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.

“We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”

Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.

A delicate transfer

“The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”

O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.

However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.

Plugging graphene’s leaks

To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.

The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.

Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.

In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.

Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.

The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.

“Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”

This research was supported in part by the Center for Clean Water and Clean Energy at MIT and KFUPM, the U.S. Department of Energy, and the National Science Foundation.

###

Written by Jennifer Chu, MIT News Office

####

For more information, please click here

Contacts:
Abby Abazorius
MIT News Office

617.253.2709

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

ARCHIVE: How to create selective holes in graphene:

ARCHIVE: Need a water filter? Peel a tree branch:

ARCHIVE: Novel membrane reveals water molecules will bounce off a liquid surface:

Related News Press

News and information

Researchers are cracking the code on solid-state batteries: Using a combination of advanced imagery and ultra-thin coatings, University of Missouri researchers are working to revolutionize solid-state battery performance February 28th, 2025

Unraveling the origin of extremely bright quantum emitters: Researchers from Osaka University have discovered the fundamental properties of single-photon emitters at an oxide/semiconductor interface, which could be crucial for scalable quantum technology February 28th, 2025

Closing the gaps — MXene-coating filters can enhance performance and reusability February 28th, 2025

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

Graphene/ Graphite

UCF researcher discovers new technique for infrared “color” detection and imaging: The new specialized tunable detection and imaging technique for infrared photons surpasses present technology and may be a cost-effective method of capturing thermal imaging or night vision, medica December 13th, 2024

Breakthrough in proton barrier films using pore-free graphene oxide: Kumamoto University researchers achieve new milestone in advanced coating technologies September 13th, 2024

A 2D device for quantum cooling:EPFL engineers have created a device that can efficiently convert heat into electrical voltage at temperatures lower than that of outer space. The innovation could help overcome a significant obstacle to the advancement of quantum computing technol July 5th, 2024

Laboratories

Giving batteries a longer life with the Advanced Photon Source: New research uncovers a hydrogen-centered mechanism that triggers degradation in the lithium-ion batteries that power electric vehicles September 13th, 2024

A 2D device for quantum cooling:EPFL engineers have created a device that can efficiently convert heat into electrical voltage at temperatures lower than that of outer space. The innovation could help overcome a significant obstacle to the advancement of quantum computing technol July 5th, 2024

Govt.-Legislation/Regulation/Funding/Policy

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

Department of Energy announces $71 million for research on quantum information science enabled discoveries in high energy physics: Projects combine theory and experiment to open new windows on the universe January 17th, 2025

Quantum engineers ‘squeeze’ laser frequency combs to make more sensitive gas sensors January 17th, 2025

Chainmail-like material could be the future of armor: First 2D mechanically interlocked polymer exhibits exceptional flexibility and strength January 17th, 2025

Discoveries

Development of 'transparent stretchable substrate' without image distortion could revolutionize next-generation displays Overcoming: Poisson's ratio enables fully transparent, distortion-free, non-deformable display substrates February 28th, 2025

Unraveling the origin of extremely bright quantum emitters: Researchers from Osaka University have discovered the fundamental properties of single-photon emitters at an oxide/semiconductor interface, which could be crucial for scalable quantum technology February 28th, 2025

Closing the gaps — MXene-coating filters can enhance performance and reusability February 28th, 2025

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

Materials/Metamaterials/Magnetoresistance

Chainmail-like material could be the future of armor: First 2D mechanically interlocked polymer exhibits exceptional flexibility and strength January 17th, 2025

Enhancing transverse thermoelectric conversion performance in magnetic materials with tilted structural design: A new approach to developing practical thermoelectric technologies December 13th, 2024

FSU researchers develop new methods to generate and improve magnetism of 2D materials December 13th, 2024

New material to make next generation of electronics faster and more efficient With the increase of new technology and artificial intelligence, the demand for efficient and powerful semiconductors continues to grow November 8th, 2024

Announcements

Development of 'transparent stretchable substrate' without image distortion could revolutionize next-generation displays Overcoming: Poisson's ratio enables fully transparent, distortion-free, non-deformable display substrates February 28th, 2025

Unraveling the origin of extremely bright quantum emitters: Researchers from Osaka University have discovered the fundamental properties of single-photon emitters at an oxide/semiconductor interface, which could be crucial for scalable quantum technology February 28th, 2025

Closing the gaps — MXene-coating filters can enhance performance and reusability February 28th, 2025

Rice researchers harness gravity to create low-cost device for rapid cell analysis February 28th, 2025

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

Development of 'transparent stretchable substrate' without image distortion could revolutionize next-generation displays Overcoming: Poisson's ratio enables fully transparent, distortion-free, non-deformable display substrates February 28th, 2025

Leading the charge to better batteries February 28th, 2025

Quantum interference in molecule-surface collisions February 28th, 2025

New ocelot chip makes strides in quantum computing: Based on "cat qubits," the technology provides a new way to reduce quantum errors February 28th, 2025

Water

Two-dimensional bimetallic selenium-containing metal-organic frameworks and their calcinated derivatives as electrocatalysts for overall water splitting March 8th, 2024

Computational system streamlines the design of fluidic devices: This computational tool can generate an optimal design for a complex fluidic device such as a combustion engine or a hydraulic pump December 9th, 2022

Taking salt out of the water equation October 7th, 2022

Scientists capture a ‘quantum tug’ between neighboring water molecules: Ultrafast electrons shed light on the web of hydrogen bonds that gives water its strange properties, vital for many chemical and biological processes July 8th, 2022

Industrial

Quantum interference in molecule-surface collisions February 28th, 2025

Boron nitride nanotube fibers get real: Rice lab creates first heat-tolerant, stable fibers from wet-spinning process June 24th, 2022

Nanotubes: a promising solution for advanced rubber cables with 60% less conductive filler June 1st, 2022

Protective equipment with graphene nanotubes meets the strictest ESD safety standards March 25th, 2022

Research partnerships

SMART researchers pioneer first-of-its-kind nanosensor for real-time iron detection in plants February 28th, 2025

Gene therapy relieves back pain, repairs damaged disc in mice: Study suggests nanocarriers loaded with DNA could replace opioids May 17th, 2024

Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024

Researchers’ approach may protect quantum computers from attacks March 8th, 2024

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




  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project