There is valuable, perfectly usable gold in electronic and mining waste. The challenge is to nab it efficiently. That’s difficult to do because gold is present in low concentrations and there are other interfering metal ions to contend with. A new metal-organic framework (MOF) can extract 23.9-karat, or 99.6% pure, gold from electronic wastewater without being bogged down by other metal ions (Chem 2026, DOI: 10.1016/j.chempr.2026.103212).
The material pulled the lustrous metal from gold mine wastewater. And it even wrung traces of gold from seawater spiked with a tiny amount of the precious metal, just 1 part per billion.
MOFs are porous, crystalline materials composed of metal clusters connected with organic linkers. Their high surface area and easy-to-tune chemistry make them ideal for pulling gold from wastewater. To do that, researchers have typically modified MOFs with chemical groups to capture gold via chemical reactions or electrostatic binding. But that approach also attracts other metal ions.
The new MOF grabs only gold. It is made of zirconium nodes interconnected with crown ethers: large ring-shaped molecules, or macrocycles, composed of repeating ether groups. Because of their negatively charged interiors, crown ethers selectively trap metal cations. But gold is usually present in solutions as anions.
Researchers made a MOF with zirconium nodes (blue central and exterior polygons) connected by crown ether ligands (red and gray structures around the circles) and loaded it with potassium cations (purple circles), creating a positively charged environment and a structure with just the right pore channels to grab gold anions from wastewater. Credit:
Zhenguo Zhang
So Feihe Huang of Zhejiang University, Jonathan Sessler of the University of Texas at Austin, and their colleagues embedded a positive charge in their crown ether–based MOF. They load the material with potassium cations by soaking it in a potassium chloride solution. The cations sit in the middle of the crown because of ion-dipole interactions between the ion and the oxygen atoms of the crown.
“The engineering approach here is to put potassium into a very controlled, rigid, stable MOF environment,” Sessler says. The positively charged environment on the inside of the macrocycle draws gold anions, and the precise dimensions and shapes of the MOF pore channels keep other anions out, he says. “This is on the frontier of anion recognition, which has always been a greater challenge than cation recognition.”
The researchers used the material to extract gold from discarded computer processor chips. They dissolved 100 chips in hydrochloric acid and added 1 g of the MOF to the leachate. After 24 h, they filtered gold-loaded MOF powder from the solution and soaked the powder in a reducing agent to recover the gold. After running this cycle three times, they recovered 490 mg of 23.9-karat gold.
This work presents a new strategy for designing materials for recovering valuable materials from waste, says Dan Li, a supramolecular chemistry expert at Jinan University. “[It] demonstrates that the synergy between supramolecular macrocycles and MOFs can deliver substantially higher selectivity and faster adsorption kinetics than commercial gold-adsorbing resins and other porous gold-recovery materials.”
The material’s adsorption capacity of 244 mg/g is lower than that of some reported MOFs, and the synthesis of the crown ether ligands is relatively costly, he says. But its selectivity for gold and recyclability could still make it useful.
Prachi Patel is a senior editor and physical sciences reporter at C&EN based in Pittsburgh.
