Cation-Dependent Gold Recovery with α-Cyclodextrin Facilitated by Second-Sphere Coordination

Zhichang Liu, Avik Samanta, Juying Lei, Junling Sun, Yuping Wang, J. Fraser Stoddart*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

81 Scopus citations

Abstract

Herein, we report an alkali metal cation-dependent approach to gold recovery, facilitated by second-sphere coordination with eco-friendly α-cyclodextrin (α-CD). Upon mixing eight salts composed of Na+, K+, Rb+, or Cs+ cations and [AuX4]- (X = Cl/Br) anions with α-, β-, or γ-CD in water, co-precipitates form selectively from the three (out of 24) aqueous solutions containing α-CD with KAuBr4, RbAuBr4, and CsAuBr4, from which the combination of α-CD and KAuBr4 affords the highest yield. Single-crystal X-ray analyses reveal that in 20 of the 24 adducts CD and [AuX4]- anions form 2:1 sandwich-type second-sphere adducts driven partially by [C-H···X-Au] interactions between [AuX4]- anions and the primary faces of two neighboring CDs. In the adduct formed between α-CD and KAuBr4, a [K(OH2)6]+ cation is encapsulated inside the cavity between the secondary faces of two α-CDs, leading to highly efficient precipitation owing to the formation of a cation/anion alternating ion wire residing inside a continuous α-CD nanotube. By contrast, in the other 19 adducts, the cations are coordinated by OH groups and glucopyranosyl ring O atoms in CDs. The strong coordination of Rb+ and Cs+ cations by these ligands, in conjunction with the stereoelectronically favorable binding of [AuBr4]- anions with two α-CDs, facilitates the co-precipitation of the two adducts formed between α-CD with RbAuBr4 and CsAuBr4. In order to develop an efficient process for green gold recovery, the co-precipitation yield of α-CD and KAuBr4 has been optimized regarding both the temperature and the molar ratio of α-CD to KAuBr4.

Original languageEnglish (US)
Pages (from-to)11643-11653
Number of pages11
JournalJournal of the American Chemical Society
Volume138
Issue number36
DOIs
StatePublished - Sep 14 2016

Funding

This work made use of the EPIC facility of the NUANCE Center at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205); the MRSEC program (NSF DMR-1121262) at the Materials Research Center; the International Institute for Nanotechnology (IIN); and the State of Illinois, through the IIN.

ASJC Scopus subject areas

  • General Chemistry
  • Biochemistry
  • Catalysis
  • Colloid and Surface Chemistry

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