Scientists have created the world’s thinnest gold foil, just one atom thick, promising many important applications in carbon dioxide conversion and hydrogen production.
To create the new material called “goldene”, the team applied a 100-year-old technique used by Japanese ironsmiths to separate layers of gold. They describe their results in the journal Nature Synthesis, Live Science reported on April 25.
Researchers are especially interested in two-dimensional materials because of their unusual optical, electronic and catalytic properties. The extremely high surface area relative to volume of these compounds means they behave very differently from chemically identical bulk solids. Many examples of 2D materials have been described since the discovery of graphene in 2004. However, the majority of materials come from nonmetals or mixed compounds. Creating a pure metal sheet just one molecule thick is much more difficult.
According to Michael Yeung, a chemist at the University of Albany, several research groups have previously created layers of gold atoms inserted inside solids such as silicon carbide coated with graphene. But separating the gold layer from this complex layered structure is very complicated because the gold atoms agglomerate into nanoparticles as soon as they lose their support.
Shun Kashiwaya, assistant professor in the Department of Physics, Chemistry and Biology at Linkinging University, Sweden, and his colleagues successfully separated a layer of gold called goldene for the first time. They started by creating a multi-layer structure of titanium, silicon and carbon, then coated the surface with gold. After 12 hours, gold particles dispersed into the material, replacing the silicon layer and creating a goldene layer inserted inside the solid mass. However, instead of removing the gold layer, the team carefully separated all the surrounding solid mass, leaving the gold layer intact.
Researchers discovered the technique when Lars Hultman, a professor in the Department of Physics, Chemistry and Biology at Linking University, searched for a chemical etching agent. Hultman found a 100-year-old method that Japanese blacksmiths used to get carbide residue out of steel. Called Murakami reagent or alkaline potassium ferricyanide, the solution removes surrounding titanium carbide without affecting the goldene layer.
To perfect the method, the research team experimented with different reaction conditions and etching solution densities. They found that adding the amino acid cysteine as a surfactant, or chemical that reduces the surface tension of a liquid, helps stabilize the separated layer and prevents gold atoms from clustering and combining into nanoparticles. The isolated goldene layer is up to 100 nanometers long and hundreds of times thinner than regular gold leaf.
Because of goldene’s enhanced chemical reactivity, it has important applications in converting carbon dioxide into fuels such as ethanol and methane, or converting water into hydrogen. The research team is looking to improve the synthesis method.