Surprising Water Behavior Detected at Nanoscale Level; What Role Do Graphene Oxide Membranes Play?

Researchers from UNSW Sydney, the University of Duisburg-Essen in Germany, GANIL in France, and Toyota Technological Institute in Japan investigating Graphene Oxide or GO membranes have detected the opposite can happen at the nanoscale level.

As asked in a Phys.org report, "Do more pores in a sieve" enable more liquid to flow through it? As material scientists have revealed, this simple question may have an unforeseen answer at the nanoscale, and it could have essential effects on the development of water filtration, hydrogen production, and energy storage.

The study demonstrates that the sieve's chemical environment and the liquid's surface tension play an astonishingly vital role in permeability.

The study investigators observed that a density of pores does not essentially result in higher water permeability. This means that more small holes do not always enable water to flow through at the nanoscale.

Graphene Oxide Membranes

The study, published in the Nano Letters journal, backed by the European Union and Humboldt Research Foundation funding, has shed new light on the mechanisms governing water flow through GO membranes.

According to the study's senior author, Rakesh Joshi, Associate Professor at the School of Materials Science & Engineering, UNSW Science.

Essentially, GO is an ultra-thin form of carbon that has exhibited promise as a material for water purification. More so, the chemical compound comprises a single layer of carbon atoms with oxygen and hydrogen atoms attached.

In chemistry, molecules can have what's identified as "functional groups" that are either water-repelling or hydrophobic or water-attracting or hydrophilic. Furthermore, the pores in graphene can either be hydrophobic or hydrophilic.

Hydrophobic or Hydrophilic

UNSW Scientia Ph.D. candidate Tobias Foller and the study's lead author explained that surprisingly, more essential for the water flux, waterflow through a membrane, is not the number of pores, "although whether the pores are hydrophobic or hydrophilic."

The lead author added that it's very unexpected as the GO layers are only a single atom thick. One expects the water to pass through the pores regardless of whether they are attracting or repelling water.

Despite many small holes in the GO filters used in this study, the researchers demonstrated a total blockage of water in the case of hydrophobic pores.

According to the study's co-author, Prof. Marika Schleberger, from Duisburg, Germany, with filters, one usually expects "more water flow with more holes."

However, in this circumstance, where there are more holes, water flow is lower, and that is because of the chemical nature of graphene oxide holes which are, in this circumstance, water-repelling.

Surface Tension Contributing to Water Interaction

The study authors also said that surface tension contributes to the water interaction as well, along with the GO pores. More so, tension occurs due to molecules, such as water, want to cling together.

When confined in a substantially small space, the bonds between water and surrounding solid surfaces can function to move the water, a similar Mirage News report specified.

This explains how trees can overcome gravity to take water from their roots up the capillaries to the leaves.

Specifically, in GO membranes, where the "capillaries" in the said case are pores generated at the scale of one-millionth of a millimeter or less, the very forces that enable water to climb tree capillaries stop it from flowing through membrane pores.

The researchers explained that when one confines water in the tiniest possible capillaries, just the size of a few atoms, the water molecules attract so much from a tight network.

Related information about graphene oxide is shown on MK Academy's YouTube video below:

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