Lawrence Livermore National Laboratory (LLNL) scientists have created the largest defect-free membranes from single-walled carbon nanotubes (CNT).
Growing these high density, cylindrical molecules on 4-inch silicon wafers and using them to create membranes with exceptional transport properties, could benefit a whole lot of low energy alternatives in applications such as desalination, pharmaceutical recovery, purification and waste treatment.
As part of their research, the scientists – under the guidance of senior Livermore scientist Francesco Fornasiero – managed to fully exploit the unique mass transport properties of carbon nanotubes as flow channels.
Said to be more than 50,000 times thinner than a human hair, these tiny channels – unlike conventional porous materials – allow for exceptionally fast gas and liquid flow that gets even faster as the tubes get smaller.
“Scaling up carbon nanotube membranes without introducing leaks is no small task,” notes lead author and LLNL postdoctoral researcher Melinda Jue.
“We rigorously control and characterize our membranes to ensure that they’re defect-free before using them to accurately measure flow enhancement.”
According to the scientists, there are 10 times more conductive nanotubes in these large area membranes than previously achieved.
“By using a high density of carbon nanotubes as transport pathways, we were able to make membranes that are 6,200 times more water permeable than predicted by theory and have water flow up to 10 times larger than commercially available membranes with similar pore size,” says Fornasiero.
He and his team also investigated the nanofiltration capability of these large-area carbon nanotube membranes and were quite happy with the results.
“You could imagine using these membranes to efficiently separate highly saline solutions where you want to remove the salt while concentrating the more valuable component.” says Jue.
According to Jue, this is significant as performance degradation due to fouling is a major obstacle in the widespread use of membrane technologies, and counteracting its effects requires treatment of the membranes with harsh chemicals.
The robust nature of carbon nanotubes and the polymer matrix also leads to excellent chemical stability, allowing for easy cleaning of the membranes.
Once the membrane gets dirty, all you need to do is clean it with bleach without having to worry about degradation like with typical polymer membranes.
Image and content: Lawrence Livermore National Laboratory
