Old but Gold (literally)!

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It is widely known that beta cyclodextrin has the best cavity for several drug molecules. But what about noble metals?

In this recent Nature publication by the Nobel prize winner sir James Fraser Stoddart a new application of BCD is explored.

Tetrabromoaurate aninos form supramolecular polymers with BCD that precipitate from aqueous solutions as cocrystals. When dibutyl carbitol (DBC) is added as an additive the efficiency of gold recovery reaches 99.8%.

After adding DBC, that serves as an additional guest for the BCD and occupies the cavity, the tetrabromoaurate anions are obliged to move to the primary faces of the BCD tori, forming a unique heterodimeric encapsulation complex.

DBC links together two BCD molecules, faced together with the secondary sites.

This supramolecular complex assembles spontaneously into stable 1D nanostructures.

Summarizing the advantages:

  • <0.3% additive is required for a >99.5% efficiency
  • the procedure is highly selective and it is not disturbed by other tetraboroanionates, like palladium or platinum
  • the gold-recovery can be performed at low concentrations (9.3 ppm)
  • no additional potassium cations are needed

Practical use of the procedure is the extraction of gold from electronic wastes at low cost and high efficiency.


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