Posted by The Cyclodextrin News blog has already reported on the new method for gold recovery. Sir Stoddart’s team published on an additive-induced gold recovery paradigm based on precisely controlling the reciprocal transformation and instantaneous assembly of the second-sphere coordinated adducts formed between β-cyclodextrin and tetrabromoaurate anions [1]. The additives initiate a rapid assembly process by co-occupying the binding cavity of β-cyclodextrin along with the tetrabromoaurate anions, leading to the formation of supramolecular polymers that precipitate from aqueous solutions as cocrystals. The efficiency of gold recovery reaches 99.8% when dibutyl carbitol is deployed as the additive. This cocrystallization is highly selective for square-planar tetrabromoaurate anions. In a laboratory-scale gold-recovery protocol, over 94% of gold in electronic waste was recovered at gold concentrations as low as 9.3 ppm. This simple protocol constitutes a promising paradigm for the sustainable recovery of gold, featuring reduced energy consumption, low cost inputs, and the avoidance of environmental pollution.
In the same issue of Nature Communication Ponchel and Monflier [2] evaluated this new method as follows:
In light of the above results, it appeared that supramolecular science, especially based on renewable natural cyclodextrins, reached a level of maturity that enables a paradigm shift. Its progress has concomitantly occurred with the development of synthetic, analytical, and characterization methods that have enabled the discovery of hierarchically ordered materials on relevant scales. In context, the second-sphere coordination has evolved as a strategic field research for the elaboration of hybrid superstructures for which an exciting future is foreseen. The recent work of Stoddart and colleagues has illustrated in a rational and elegant manner the design of a class of metal-organic superstructures, built from different types of well-defined components, and formed by the participation of cooperative multi-recognition and infinite self-assembly (from the solution to the solid-sate). This consortium brought evidence of the outstanding selective gold extraction application carried out under benign conditions.
[1] H., Wang, Y., Tang, C. …Stoddart, F.: High-efficiency gold recovery by additive-induced supramolecular polymerization of β-cyclodextrin. Nat Commun 14, 1284 (2023). https://doi.org/10.1038/s41467-023-36591-0
[2] Ponchel, A., Monflier, E. Application of cyclodextrins as second-sphere coordination ligands for gold recovery. Nat Commun 14, 1283 (2023). https://doi.org/10.1038/s41467-023-36700-z