More liquid can flow through a sieve. The seemingly simple question may have important implications in the development of water purification, energy storage and hydrogen production.
Researchers from the University of Duisburg-Essen in Germany, GANIL in France, and the Toyota Technological Institute in Japan are working with Graphene Oxide (GO) membranes. The research shows that the chemical environment of the sieve and the surface tension of the liquid have an effect on permeability.
In other words, having more tiny holes doesn't always allow water to flow through at the smallest size. The study was supported by the European Union and the research foundation.
If you create more holes in a sieve, it will become more porous. A senior author of the study from the School of Materials Science & Engineering, the University of New South Wales, says that the results of the experiment were different than what they had expected.
Changing the environment.
GO is a thin form of carbon that has the potential to be used for water purification. Oxygen and hydrogen atoms are attached to a single layer of carbon atoms. Imagine scattering LEGO bricks on the floor with the carbon atoms and the oxygen and hydrogen atoms.
Molecules can have functional groups that are either water- repelling or water-attracting. The pores in Graphene can be made of different types of materials.
According to the lead author of the study, the number of pores is not the most important factor for the water flux. The GO layers are only a single atom thick. If they attract or repel water, one expects the water to go through the pores.
There were many tiny holes in the GO filters used in the research, but they showed a complete block of water.
Water flow with more holes is what you expect with filters. The study from Duisburg found that where we have more holes, the water flow is lower.
Surface tension has unusual effects.
The surface tension contributes to the water interaction with the GO pores. The surface tension is caused by the molecule wanting to stick together. The bonds between water and surrounding solid surfaces can act to move the water when it's in a small space. This shows how trees can take water from their roots up to their leaves.
The very forces that allow water to climb tree capillaries prevent it from flowing through the GO membranes.
Water attracts itself so much that it forms a tight network in the smallest capillaries. Mr. Foller says that the network is so strong that it doesn't allow the molecule to be released and passed through the sieve.
There are a variety of applications for ultra fine sieves. Liquid transport in atomic sieves could be improved thanks to the researchers' findings.
Mr. Foller says that by understanding which parameters will increase or decrease water flux, we can improve many possible applications of graphene oxide. We hope that other engineers and scientists can use this new knowledge to improve their own devices and lead to new developments in the future.
More information: Tobias Foller et al, Mass Transport via In-Plane Nanopores in Graphene Oxide Membranes, Nano Letters (2022). DOI: 10.1021/acs.nanolett.2c01615 Journal information: Nano Letters
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