Stable Zirconium-Piperazine Metal–Organic Frameworks for Efficient Gold Recovery

Gold’s importance in various industries, the ever-rising demand for electronics, and shrinking gold reserves all underscore the pressing need to develop effective gold recovery methods from waste. In this study, we systematically evaluate several large-pore Zirconium-carboxylate Metal–Organic Frameworks (Zr-MOFs) having slightly varied internal surface functionality (-H, -CH 3, -NH 2, and -NO 2 ) in gold recovery from acidic, simulated e-waste solutions. We compare two Zr-MOFs constructed from oligophenylene ligands with four MOFs built from structurally analogous piperazine-based ligands, including two unreported frameworks. The piperazine-based frameworks offer a critical sustainability advantage: by replacing the central benzene core with piperazine, they eliminate the need for expensive Pd-catalyzed coupling chemistry required for oligophenylene synthesis. In this work, we demonstrate for the first time that Zr-piperazine MOFs exhibit stability in acidic conditions, significantly surpassing their oligophenylene-based counterparts. One developed Zr-piperazine MOF, functionalized with both amine and methyl groups, substantially outperforms all analogs, displaying the highest stability alongside a gold adsorption capacity of up to 1826 mg/g and rapid adsorption kinetics in a 40 ppm gold solution. X-ray Absorption Near-Edge Structure (XANES) studies reveal distinct gold adsorption mechanisms for primary versus tertiary amines. These findings establish piperazine-based building blocks as promising candidates for designing selective gold adsorbents for e-waste recovery applications.