Robert Hurt, Ph.D.
A new strategy to design nanomaterials to better filter contaminants from water overcomes previous limitations, according to a new NIEHS-funded study.
Graphene oxide has already been used as a highly selective membrane. However, nanosheets typically assemble in horizontal layers, creating long narrow channels that liquid must pass through. To improve the usefulness of graphene oxide nanosheets for filtering contaminants from liquid, the researchers modified how the sheets assemble to create shorter vertical nanochannels. This approach reduces the distance water must pass through while optimizing the amount of contact it has with the membrane.
The researchers found that by stacking nanosheets on a stretched elastic substrate and releasing the tension, the graphene sheets then wrinkled into hundreds of sharp peaks and valleys. Because the sheets and the substrate both carried a negative electrical charge, the researchers determined adding zirconium as a positive ion helped optimize the membrane. Then the researchers used epoxy to encase and stabilize the wrinkled structure and trimmed away the top and bottom of the zig-zag film to create open channels. Their technique increased the active area of the membrane 300-fold compared to simply tilting a flat nanosheet by 90 degrees.
In proof-of-concept tests, the team demonstrated that water vapor could easily pass through the vertically aligned zirconium-graphene membranes, while the organic molecules hexane and 2-propanol could not. They also showed that their strategy successfully retained molecular selectivity while remaining stable at high temperatures and resistant to swelling, all important factors for scaling up the approach.
Citation: Liu M, Weston PJ, Hurt RH. 2021. Controlling nanochannel orientation and dimensions in graphene-based nanofluidic membranes. Nat Commun 12(1):507.