posted on 2020-08-13, 16:40authored byHuang Wu, Leighton O. Jones, Yu Wang, Dengke Shen, Zhichang Liu, Long Zhang, Kang Cai, Yang Jiao, Charlotte L. Stern, George C. Schatz, J. Fraser Stoddart
Developing an extremely
efficient and highly selective process for gold recovery is urgently
desired for maintaining a sustainable ecological environment. Herein,
we report a highly efficient gold-recovery protocol on the basis of
the instantaneous assembly between cucurbit[6]uril (CB[6]) and [AuX4]− (X = Cl/Br) anions. Upon mixing CB[6]
with the four gold-bearing salts MAuX4 (M = H/K, X = Cl/Br)
in aqueous solutions, yellow or brown coprecipitates form immediately,
as a result of multiple weak [Au–X···H–C]
(X = Cl/Br) hydrogen-bonding and [Au–X···C=O]
(X = Cl/Br) ion-dipole interactions. The gold-recovery efficiency,
based on CB[6]·HAuCl4 coprecipitation,
reaches 99.2% under optimized conditions. In the X-ray crystal superstructures,
[AuCl4]− anions and CB[6] molecules adopt
an alternating arrangement to form doubly connected supramolecular
polymers, while [AuBr4]− anions are accommodated
in the lattice between two-dimensional layered nanostructures composed
of CB[6] molecules. DFT calculations have revealed that the binding
energy (34.8 kcal mol–1) between CB[6] molecules
and [AuCl4]− anions is higher than that
(11.3–31.3 kcal mol–1) between CB[6] molecules
and [AuBr4]− anions, leading to improved
crystallinity and higher yields of CB[6]·MAuCl4 (M = H/K) coprecipitates. Additionally, a laboratory-scale
gold-recovery protocol, aligned with an attractive strategy for the
practical recovery of gold, was established based on the highly efficient
coprecipitation of CB[6]·HAuCl4. The use of CB[6] as a gold extractant provides us with a
new opportunity to develop more efficient processes for gold recovery.