Home > Press > Laying down a discerning membrane
Abstract:
One of the thinnest membranes ever made is also highly discriminating when it comes to the molecules going through it. Engineers at the University of South Carolina have constructed a graphene oxide membrane less than 2 nanometers thick with high permeation selectivity between hydrogen and carbon dioxide gas molecules.
The selectivity is based on molecular size, the team reported in the journal Science. Hydrogen and helium pass relatively easily through the membrane, but carbon dioxide, oxygen, nitrogen, carbon monoxide and methane permeate much more slowly.
"The hydrogen kinetic diameter is 0.289 nm, and carbon dioxide is 0.33 nm. The difference in size is very small, only 0.04 nm, but the difference in permeation is quite large" said Miao Yu, a chemical engineer in USC's College of Engineering and Computing who led the research team. "The membrane behaves like a sieve. Bigger molecules cannot go through, but smaller molecules can."
In addition to selectivity, what's remarkable about the USC team's result is the quality of the membrane they were able to craft on such a small scale. The membrane is constructed on the surface of a porous aluminum oxide support. Flakes of graphene oxide, with widths on the order of 500 nm but just one carbon atom thick, were deposited on the support to create a circular membrane about 2 square centimeters in area.
The membrane is something of an overlapping mosaic of graphene oxide flakes. It's like covering the surface of a table with playing cards. And doing that on a molecular scale is very hard if you want uniform coverage and no places where you might get "leaks." Gas molecules are looking for holes anywhere they can be found, and in a membrane made up of graphene oxide flakes, there would be two likely places: holes within the flakes, or holes between the flakes.
It's the spaces between flakes that have been a real obstacle to progress in light gas separations. That's why microporous membranes designed to distinguish in this molecular range have typically been very thick. "At least 20 nm, and usually thicker," said Miao. Anything thinner and the gas molecules could readily find their way between non-uniform spaces between flakes.
Miao's team devised a method of preparing a membrane without those "inter-flake" leaks. They dispersed graphene oxide flakes, which are highly heterogeneous mixtures when prepared with current methods, in water and used sonication and centrifugation techniques to prepare a dilute, homogeneous slurry. These flakes were then laid down on the support by simple filtration.
Their thinnest result was a 1.8-nm-thick membrane that only allowed gas molecules to pass through holes in the graphene oxide flakes themselves, the team reported. They found by atomic force microscopy that a single graphene oxide flake had a thickness of approximately 0.7 nm. Thus, the 1.8-nm-thick membrane on aluminum oxide is only a few molecular layers thick, with molecular defects within the graphene oxide that are essentially uniform and just a little too small to let carbon dioxide through easily.
The advance has a range of potential applications. With widespread concerns about carbon dioxide as a greenhouse gas, the efficient separation of carbon dioxide from other gases is a high research priority. Moreover, hydrogen represents an integral commodity in energy systems involving, for example, fuel cells, so purifying it from gas mixtures is also an active area of interest.
Yu also notes that the dimensions of the molecular sieve are on the order of the size of water, so, for example, purifying the copious amounts of tainted water produced by hydraulic fracturing (fracking) is another possibility.
Being able to reduce membrane thickness - and by an order of magnitude - is a big step forward, Yu said. "Having membranes so thin is a big advantage in separation technology," he said. "It represents a completely new type of membrane in the separation sciences."
####
For more information, please click here
Contacts:
Steven Powell
803-777-1923
Copyright © University of South Carolina
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.
Related News Press |
News and information
Simulating magnetization in a Heisenberg quantum spin chain April 5th, 2024
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Graphene/ Graphite
NRL discovers two-dimensional waveguides February 16th, 2024
Discoveries
Chemical reactions can scramble quantum information as well as black holes April 5th, 2024
New micromaterial releases nanoparticles that selectively destroy cancer cells April 5th, 2024
Utilizing palladium for addressing contact issues of buried oxide thin film transistors April 5th, 2024
Materials/Metamaterials/Magnetoresistance
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
Focused ion beam technology: A single tool for a wide range of applications January 12th, 2024
Announcements
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Environment
Billions of nanoplastics released when microwaving baby food containers: Exposure to plastic particles kills up to 75% of cultured kidney cells July 21st, 2023
Energy
Development of zinc oxide nanopagoda array photoelectrode: photoelectrochemical water-splitting hydrogen production January 12th, 2024
Shedding light on unique conduction mechanisms in a new type of perovskite oxide November 17th, 2023
Inverted perovskite solar cell breaks 25% efficiency record: Researchers improve cell efficiency using a combination of molecules to address different November 17th, 2023
The efficient perovskite cells with a structured anti-reflective layer – another step towards commercialization on a wider scale October 6th, 2023
Water
Taking salt out of the water equation October 7th, 2022
Fuel Cells
Current and Future Developments in Nanomaterials and Carbon Nanotubes: Applications of Nanomaterials in Energy Storage and Electronics October 28th, 2022
The latest news from around the world, FREE | ||
Premium Products | ||
Only the news you want to read!
Learn More |
||
Full-service, expert consulting
Learn More |
||