Valence Selective Gold Precursor Synthesis From Electronic Waste via Programmable Coordination Chemistry

Gold precursor salts are essential to modern catalysis, electronics, and chemical manufacturing, yet their production remains decoupled from sustainable resources. Here, we report a hydrogel that converts gold ions from electronic waste leachates into valence selective gold precursors without metallic intermediates. Through coordination and pH-programmed chemistry, the captured gold ions are converted into hydrogen tetrachloroaurate (HAuCl₄.4H₂O), hydrogen tetrabromoaurate (HAuBr₄.3H₂O), potassium dicyanoaurate (K[Au(CN)₂]), and sodium bis(sulfito)aurate (Na₃[Au(SO₃)₂]), representing Au(III) and Au(I) salts. The material demonstrates a gold absorption capacity of 837 mg/g and retains extraction efficiencies near 98% despite the presence of surplus competing metal ions. All gold precursors are acquired with quantitative yield and purity exceeding 99.9%, while the hydrogel maintains efficacy during numerous successive cycles. This work establishes a scalable route for transforming electronic waste into value-added gold feedstocks, advancing sustainable chemical manufacturing and circular materials design.