Ultra-Efficient and Selective Gold Separation via Second-Sphere Coordination of Aurous Dihalide Using a Nonporous Amorphous Superadsorbent.

Abstract

The escalating demand for gold, coupled with dwindling terrestrial reserves, underscores the urgent need for innovative separation strategies, including e-waste recycling and seawater extraction. However, the development of ultra-efficient, highly selective adsorbents capable of recovering trace amounts of gold from complex aquatic matrices remains a formidable challenge. Herein, a covalent organic superphane cage is reported as a nonporous amorphous superadsorbent (NAS) for selective and efficient gold recovery via intermolecular second-sphere coordination of AuBr₂⁻ (or AuCl₂⁻) ions, subsequently converted to metallic gold through disproportionation. NAS demonstrates outstanding performance, including an exceptional gold uptake capacity of 2750 mg g⁻¹, ultrafast adsorption kinetics (40 s), broad pH tolerance (1-11, up to 6 M acids), and remarkable gold uptake even in 36 wt.% HCl solution (821 mg g⁻¹). NAS achieves over 99% selective gold recovery, even amidst excess competing ions, retaining efficacy across 30 regeneration cycles. Its versatile and scalable design enables applications in gold separation from gold-bearing e-waste, catalytic residues, gold ores, and seawater. A large-scale trial recovered 23.8 Karat gold from printed circuit board leachates, positioning NAS as a sustainable and eco-friendly solution for industrial and environmental gold recovery.