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.