A new impermeable form of graphene oxide could be the ultimate protective coating

September 19, 2014

Water permeation through a brick without (left) and with (right) “graphene paint” coating (credit: Y. Su et al./ArXiv)

A new form of graphene oxide could be the ultimate protective coating and could have a significant impact on chemical, pharmaceutical, and electronic industries, according to University of Manchester researchers.

For example, applied as paint, it could provide an ultra-strong, non-corrosive coating for a wide range of industrial applications.

Besides being protective, the new material is mechanically nearly as tough as graphene itself, the strongest known material.

The University of Manchester team is led by Rahul Nair and Sir Andre Geim, who was awarded the Nobel Prize in Physics 2010 for his work in first reliably producing graphene in the lab. However, while graphene is impermeable to all gases and liquids, it has proved challenging to develop large-area defectless graphene films suitable for industrial use, they previously found.

So Nair and Geim developed multilayer films made from graphene oxide. These are vacuum-tight under dry conditions, but if exposed to water (or water vapor), they act as molecular sieves, allowing passage of small molecules below a certain size (which could have huge implications for water purification). That’s because graphene-oxide films consist of millions of small flakes stacked randomly on top of each other, leaving nano-sized capillaries between them.

‘Graphene paint’: a new impermeable form of graphene oxide

However, the researchers were able to tightly close these nanocapillaries in graphene oxide. The trick: using simple chemical “reduction” treatments (specifically, the use of hydroiodic acid), creating “reduced graphene oxide” (RDO) films that are stronger mechanically and completely impermeable to everything — gases, liquids or strong chemicals — at least more than 100 nanometers in thickness, as the researchers note in an article published in Nature Communications (also available as an open-access ArXiv article).

For example, the researchers demonstrate that glassware or copper plates covered with “graphene paint” (as the researchers call this form of RDO) can be used as containers for strongly corrosive acids.

“Graphene paint has a good chance to become a truly revolutionary product for industries that deal with any kind of protection either from air, weather elements or corrosive chemicals,” said Nair, including medical, electronics, nuclear, and shipbuilding industries.

Yang Su, the first author in this work added: “Graphene paint can be applied to practically any material, independently of whether it’s plastic, metal or even sand. For example, plastic films coated with graphene could be of interest for medical packaging to improve shelf life because they are less permeable to air and water vapor than conventional coatings. In addition, thin layers of graphene paint are optically transparent.”

Abstract of Nature Communications paper

Flexible barrier films preventing permeation of gases and moistures are important for many industries ranging from food to medical and from chemical to electronic. From this perspective, graphene has recently attracted particular interest because its defect-free monolayers are impermeable to all atoms and molecules. However, it has been proved to be challenging to develop large-area defectless graphene films suitable for industrial use. Here we report barrier properties of multilayer graphitic films made by gentle chemical reduction of graphene oxide laminates with hydroiodic and ascorbic acids. They are found to be highly impermeable to all gases, liquids and aggressive chemicals including, for example, hydrofluoric acid. The exceptional barrier properties are attributed to a high degree of graphitization of the laminates and little structural damage during reduction. This work indicates a close prospect of graphene-based flexible and inert barriers and protective coatings, which can be of interest for numerous applications.