Gold has been prized since ancient times for its long-lasting shine. Now, researchers at Tulane University have discovered an important reason why precious metals resist tarnishing. Their findings show that gold’s durability is not determined solely by its chemical properties. Instead, the arrangement of atoms on the surface plays a key role.
This study physical review letterfound that certain gold surface atoms spontaneously migrate into a protective pattern that makes it very difficult for oxygen to react with the metal.
This newly identified behavior helps explain why gold jewelry, coins, and other objects can maintain their shine for centuries. It could also help scientists develop more effective gold-based catalysts for industrial production and clean energy technology.
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“People have generally assumed that gold doesn’t change color because it doesn’t interact strongly with oxygen,” says Matthew Montemore, an associate professor of chemical engineering at Tulane’s School of Science and Engineering. “What we show is that in the two most common gold surface types, the atoms on the surface actually rearrange themselves to make the gold much more resistant to oxidation.”
To investigate this process, Montemore and co-author Santu Biswas, a postdoctoral fellow in Tulane University’s Department of Chemical and Biomolecular Engineering, used computer simulations to model how atoms and electrons behave. They investigated how oxygen molecules interact with two common types of gold surfaces.
The simulations revealed that if the surface atoms did not rearrange, the oxygen molecules could more easily split and react with the gold. Instead, atomic restructuring dramatically limits these reactions.
The researchers say these reorganized surfaces reduce oxygen reactions by a factor of 1 billion to 1 trillion. In fact, they create an atomic-scale protective barrier that allows gold to shine almost forever.
What this discovery means for gold catalysts
The study not only explains one of gold’s most striking properties, but also could have important implications for catalysis.
Gold-based catalysts that accelerate chemical reactions are already used in several industrial oxidation processes. However, gold’s high resistance to oxygen, a property that makes it ideal for jewelry and electronics, also makes it less effective in some chemical manufacturing and energy-related reactions.
For example, gold-palladium catalysts are used to make vinyl acetate, an essential ingredient in many plastics and other products. Scientists are also investigating gold catalysts for applications such as removing carbon monoxide from car exhaust and producing propylene oxide, another widely used industrial chemical.
“If you can trick gold into dissociating oxygen, it could actually become a very effective catalyst for certain reactions,” Montemore said. “Our study suggests new strategies to potentially do that by preventing or reversing these surface rearrangements.”
New strategies for better catalysts
Until now, efforts to improve gold catalysts have focused primarily on combining gold with other metals or using small gold nanoparticles on oxide surfaces.
The new findings suggest there may be another path forward. By controlling the shape of gold’s surface and the arrangement of its atoms, researchers may be able to enhance the metal’s catalytic performance while gaining a deeper understanding of why gold has remained discolored throughout history.
