Synthetic 2D graphene oxide nanosheets from commercial carbon fibres

A team of researchers has developed ¹ a reproducible and scalable method for producing graphene oxide (GO) nanosheets from commercial carbon fibres, marking a breakthrough in sustainable nanomaterial synthesis.

The process involves exfoliating carbon fibres with nitric acid, which provides high yields of one-atom-thick sheets of graphene oxide with characteristics comparable to commercial GO sourced from mined graphite.

Graphene oxide is a widely studied nanomaterial that can be used in car batteries when its thin sheets stack together, forming layers similar to graphite. It is also useful in high-performance composites, water purification and electronic devices. However, synthesis from mined graphite requires harsh chemicals and often results in material inconsistencies due to variations in graphite purity.

Richard Olsson, professor in polymeric materials at KTH Royal Institute of Technology (Sweden), says the proof of concept was carried out with carbon fibers derived from polyacrylonitrile (PAN), a widely available polymer that undergoes high-temperature oxidation and graphitization. He says the method could be duplicated with other raw sources, such as raw sources such as biomass or forest industry sidestreams.

Olsson points to the electric vehicle battery market as one that can benefit from the new technology. “The core of graphite battery functionality can be found in the layered graphene inside, which can be harvested from commercial carbon fibres using this method,” he says.

“The future of auto manufacturing will build on battery-based power, and the question is where the graphite will be sourced? They are going to need alternatives.”

The method consists of transforming the carbon fibres using the process of electrochemical oxidation in a bath of water and nitric acid. The bath acts as a conductor and when an electric current is sent through carbon fibre, the material begins to lose electrons which transforms the surface much the same way that oxidization appears as rust on a car. In this case, the transformation causes layers of nanoscale graphene oxide to peel off from the carbon fibres’ surface.

The study discovered a window in which just 5 percent nitric acid was perfect for creating these tiny nanosheets, ranging from 0.1 to 1 micrometer in size, with a uniform thickness of about 0.9 nanometres. Notably, the GO nanosheets synthesized this way emerged in circular and elliptical shapes, in contrast to the polygonal shapes typical of GO synthesized from natural, mined graphite.

Compared to existing synthetic methods, the new approach delivers a high yield of 200 milligrams of GO per gram of carbon fibre. This efficient conversion rate makes it viable for large-scale production, addressing a key challenge in nanomaterial synthesis, he says.

To ensure the nanosheets met quality standards, the researchers examined and measured the properties and structure of the material with a number of advanced techniques.

The study also explored methods to remove protective polymer coatings from commercial carbon fibres before oxidation, heating at 580°C for two hours and shock-heating to 1200°C for three seconds—both proving effective. The research demonstrated that the nature of electrical conduction within the fibres plays a crucial role in the electrochemical exfoliation process.

Olsson says the next steps for the researchers include investigating biobased sources for carbon fibres, delving deeper into how the process works.