Golden Graphene: Researchers Successfully Synthesize “Goldene”

Scientists at Linköping University, Sweden, have successfully synthesized single-atom–thick sheets of gold for the first time. Their new material has been dubbed “goldene”, in a nod to the more well-known 2D carbon material, graphene.

According to the researchers, goldene could one day be used in applications such as carbon dioxide conversion, hydrogen production and the production of value-added chemicals, among others. The research is published in Nature Synthesis.

In search of “goldene”

The discovery and synthesis of graphene – an allotrope of carbon forming a single layer of carbon atoms – prompted significant interest in the development of alternative 2D materials. Gold became one of the elements at the forefront of these efforts, due to the already apparent usefulness of gold nanoparticles in electronics and biomedicine. But synthesizing a 2D material comprised solely of metals turned out to be a very difficult task, due to the metal’s tendency to lump together. 

“If you make a material extremely thin, something extraordinary happens – as with graphene. The same thing happens with gold. As you know, gold is usually a metal, but if single-atom–layer thick, the gold can become a semiconductor instead,” explained Shun Kashiwaya, a researcher at the Materials Design Division at Linköping University and the study’s first author.

To succeed in creating goldene, the Linköping University team used a 3D base material where gold is embedded between other layers of titanium and carbon. This technique is called intercalation.

“We had created the base material with completely different applications in mind,” said senior study author Lars Hultman, a professor of thin film physics at Linköping University. “We started with an electrically conductive ceramic called titanium silicon carbide, where silicon is in thin layers. Then the idea was to coat the material with gold to make a contact. But when we exposed the component to high temperature, the silicon layer was replaced by gold inside the base material.”

This created a material called titanium gold carbide. But this material has existed for years – the trouble for researchers has always been working out how to extract these gold sheets from the 3D base material.

Japanese smithing technique releases goldene

In Japanese forging art, smiths use a chemical known as Murakami’s reagent to etch away carbon residue and change the color of steel for knife making. Hultman and Kashiwaya wondered whether it might be possible to use a modified version of Murakami’s reagent to etch away the titanium and carbon in their titanium gold carbide material, leaving the goldene sheets behind.

“I tried different concentrations of Murakami’s reagent and different time spans for etching. One day, one week, one month, several months. What we noticed was that the lower the concentration and the longer the etching process, the better. But it still wasn’t enough,” Kashiwaya said.

In the end, the researchers found that carrying out the etching process in the dark allowed the goldene sheets to be released – carrying out the same process in light led to the development of cyanide, which ruined the material. In a final step, the team applied a long-molecule surfactant to the released goldene sheets to prevent them from curling up or lumping together.

“The goldene sheets are in a solution, a bit like cornflakes in milk. Using a type of ’sieve’, we can collect the gold and examine it using an electron microscope to confirm that we have succeeded, which we have,” said Kashiwaya.

Goldene is interesting because it exhibits some very special properties. Gold has two free bonds when two-dimensional, which the researchers say could lead to the application of goldene in carbon dioxide conversion, hydrogen-generating catalysis, selective production of value-added chemicals, hydrogen production, water purification, communications and much more.

It is also possible that some applications that currently use thin wafers of gold might benefit from replacing those with goldene, saving on the amount of precious gold that needs to be used in industry.

Next, the team is planning to investigate whether similar methodologies could be used to create 2D sheets of other noble metals. They also intend to work on identifying future applications for such materials.

Reference: Kashiwaya S, Shi Y, Lu J, et al. Synthesis of goldene comprising single-atom layer gold. Nat Synth. 2024:1-8. doi: 10.1038/s44160-024-00518-4

This article is a rework of a press release issued by Linköping University. Material has been edited for length and content.