Gold's surface atoms help explain its resistance to tarnish
Tulane researchers say gold atoms form surface patterns that sharply limit oxygen reactions, a finding that could guide better catalysts.
By Tom Brennan · Health & Medicine Correspondent
3 min read
Researchers at Tulane University say they have identified an atomic-scale reason gold keeps its shine for long periods: atoms on some gold surfaces reorganize into patterns that block oxygen from reacting with the metal. The finding matters beyond jewelry, because the same resistance to oxygen can limit gold’s usefulness in catalysts for manufacturing and clean-energy chemistry.
The work, published in Physical Review Letters, examined how oxygen behaves when it meets two common types of gold surfaces. According to Tulane, the research found that surface structure, not only gold’s chemical makeup, plays a central role in the metal’s resistance to oxidation.
Matthew Montemore, an associate professor of chemical engineering in Tulane’s School of Science and Engineering, said the common explanation has been that gold does not react strongly with oxygen. Tulane said the new study adds a second mechanism: on two widely studied gold surface types, the outer atoms shift into arrangements that make oxygen reactions far less likely.
Simulations point to a protective surface pattern
Montemore and Santu Biswas, a postdoctoral fellow in Tulane’s Department of Chemical and Biomolecular Engineering, used computer simulations to study atoms and electrons at gold surfaces. Tulane said the researchers modeled how oxygen molecules interact with those surfaces and what changes when the surface atoms reconstruct.
The simulations showed that oxygen molecules would split more readily and react with gold if the surface atoms stayed in an unreconstructed arrangement, according to the university. When the atoms reorganized, the surface became far less favorable for those oxygen-splitting reactions.
Tulane said the reconstructed surfaces suppressed oxygen reactions by a factor ranging from a billion to a trillion. That scale of reduction, according to the researchers, helps explain why gold objects such as jewelry and coins can keep their appearance over very long periods.
The journal paper, titled “Role of Reconstruction in the Inertness of Gold toward Oxygen,” was written by Biswas and Montemore. Tulane said the study focused on the metal’s surface behavior rather than on bulk properties inside the material.
Why catalyst researchers care
The same surface behavior that helps gold resist oxidation can be a drawback in catalysis, according to Tulane. Gold-based catalysts are already used in some industrial oxidation processes, but their reluctance to activate oxygen can make them less effective for certain reactions.
Tulane cited gold-palladium catalysts used in vinyl acetate production, a process tied to plastics and other products. The university also said researchers have been studying gold catalysts for uses including carbon monoxide removal from vehicle exhaust and propylene oxide production.
According to Montemore, making gold split oxygen more effectively could improve its performance as a catalyst for some reactions. Tulane said the study suggests one possible route: prevent or reverse the surface rearrangements that protect gold from oxidation.
Past efforts to improve gold catalysts have focused on approaches such as combining gold with other metals or placing tiny gold particles on oxide surfaces, according to Tulane. The new work points to surface geometry and atomic arrangement as another factor scientists may try to control.
Tulane said the findings could help researchers design more effective gold-based catalysts while giving a clearer explanation for a familiar property of the metal. The study connects gold’s long-lasting brightness with the behavior of atoms at its outermost surface.
This story draws on original reporting from ScienceDaily.