Post-synthesis functionalization of KOH-activated carbon with quaternary ammonium moiety for improved adsorption of monovalent gold

Abstract

Activated carbon (AC) has been widely applied for gold recovery and remains the most preferred adsorbent, owing to its good physicochemical and adsorption properties. Among various available activation agents, KOH is reported to produce ACs with high yields, well-defined pore sizes, ultra-high specific surface areas and high reactivities. In this study, post-synthesis functionalization of KOH-AC with a quaternary ammonium moiety was carried out with the aim of converting an agro waste precursor into a high-value AC and improving the adsorption efficiency for monovalent gold contained in potassium dicyanoaurate (1) complex, i.e., K[Au(CN2)], via an environmentally friendly approach. The synthesis process commenced with pre-carbonization and activation under nitrogen environment, followed by chemical functionalization. The crystallinity, pore structure, atomic energy binding states and Au(I) loading capacity were investigated through characterization and batch adsorption studies. The experimental maximum equilibrium adsorption capacity was 513.52 ± 18.52 mg/g, however, this may further reach 749.28 ± 34.79 mg/g, according to the Langmuir isotherm model. Finally, it was possible to regenerate the spent AC with a mixture of 1 M KCN and NaOH, making it potentially suitable for application on a larger scale.