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Nanoporous gold forms ultrathin walls and large pores

Synthesis method based on bulky calixarene gold clusters yields an unusual combination of structural features

by Mitch Jacoby
September 25, 2017 | A version of this story appeared in Volume 95, Issue 38

The artistic image depicts a synthesis method for forming a highly porous form of gold.
Credit: Chem. Commun.
In an electrochemical synthesis, hydrogen bubbles serve as templates in the formation of a hexagonally ordered, ultraporous form of gold.

Nanostructured gold has shown itself useful for catalysis, energy harvesting, electronics, and other applications. With its performance closely tied to the specifics of the precious metal’s nanoscale structure, researchers have explored various ways of customizing how the material is prepared. A team led by Alexander Katz and Alexis T. Bell of the University of California, Berkeley, has come up with a synthesis method based on colloidal assembly of gold clusters that yields nanoporous gold with exceptionally thin walls and large pores. Whereas most preparation methods lead to nanoporous gold with walls 30 nm or thicker and pores with diameters comparable to the wall thickness, the new method produces walls as thin as 10 nm and pores with diameters up to several hundred nanometers (Chem. Commun. 2017, DOI: 10.1039/c7cc05116f). That unusual combination of structural features significantly increases exposure of the gold atoms, which should enhance the material’s performance in applications. The team creates calixarene-phosphine-capped gold clusters and then uses an electrochemical reduction method that drives the metal clusters to assemble in a hexagonal-close-packed array. The metal framework is templated by hydrogen bubbles that form from water at an electrode surface. A key feature of the method is the use of the bulky ligands, which prevent the clusters from coalescing uncontrollably.


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