From e-waste to gold: the path to CO₂ sustainability

A Cornell University-led research team has developed a method to extract gold from e-waste and use the recovered precious metal as a catalyst to convert the greenhouse gas carbon dioxide (CO2) into organic materials.

According to Amin Zadehnazari, a postdoctoral researcher in Yongkeun Joh Associate’s Alireza Abbaspourrad lab, this method has the potential to provide a sustainable use for some of the approximately 50 million tons of e-waste discarded each year. However, only 20% of that is recycled. Professor of Food Chemistry and Raw Materials Technology, Faculty of Agriculture and Life Sciences.

Zadenazari synthesized a pair of vinyl-bonded covalent organic frameworks (VCOFs) to remove gold ions and nanoparticles from the circuit boards of discarded electronic devices. One of his VCOFs was shown to selectively capture 99.9% of the gold from the device, while capturing only small amounts of other metals such as nickel and copper.

“Gold-filled COFs can be used to convert CO2 into useful chemicals,” Zadenazari said. “By converting CO2 into value-added substances, we not only reduce the demand for waste disposal, but also have environmental and practical benefits. This is a kind of win-win for the environment. ”

Abbaspourrad is the corresponding author and Zadehnazari first author of “Recycling E-waste Into Gold-loaded Covalent Organic Framework Catalysts for Terminal Alkyne Carboxylation,” published in Nature Communications.

Electronic waste is a literal goldmine. It is estimated that one tonne of electronic waste contains at least 10 times more gold than one tonne of ore from which gold is extracted. And with 80 million tonnes of e-waste expected to be generated by 2030, finding ways to recover that precious metal is becoming increasingly important.

Traditional methods of recovering gold from e-waste contain strong chemicals such as cyanide, which pose environmental risks. Zadenazari’s method is achieved without the use of harmful chemicals by using chemisorption, or the attachment of particles to a surface.

Covalent organic frameworks (COFs) are porous, crystalline materials known for multiple potential applications, including chemical sensing and energy storage. Zadehnazari synthesized two VCOFs using tetrathiafulvalene (TTF) and tetraphenylethylene (TPE) as building blocks.

TTF-COF showed excellent gold adsorption due to its richness in sulfur, to which gold has a natural affinity. In addition to exhibiting high adsorption capacity, TTF-COF withstood 16 washes and reuses with little loss of adsorption efficiency.

Then, under a CO2 ambient pressure of 50 degrees Celsius (122 degrees Fahrenheit), the resulting gold-filled COFs efficiently converted CO2 to organic matter via carboxylation.

Other methods of recovering gold and other precious metals from e-waste are typically not as selective as Zadenazari’s idea and create impurities, Avasporad said.

“It is very important to know how much gold and other precious metals are in these types of electronic devices and to be able to recover them in a way that allows selective recovery of the metal (in this case gold) that is needed.” said Avasporad.