Cooking Up Decontaminants in Your Kitchen?

Forget the laboratory - substances that can solve environmental problems by capturing carbon dioxide, decontaminating water and cleaning up pollutants can be easily created in a kitchen, a new study shows.

In a paper published in Nature Communications, UNSW chemical engineers shone a light on the mysterious world of liquid metals and their role as catalysts to speed up chemical processes using low amounts of energy.

Professor Kourosh Kalantar-Zadeh, an author of the study said, “Anyone with a shaker and a cooktop at home in their kitchen can make catalysts that can be used for CO2 conversion, cleaning water and other pollutants. They can do this by using a combination of liquid metals like gallium, indium, bismuth and tin in alloys that can be melted under 300^oC on a cooktop or in an oven.”

Kalantar-Zadeh and colleague Dr Jianbo Tang showed that by heating an alloy of bismuth and tin, the metal melted at a point much lower than if you were to heat each metal individually. Substances that behave like this are said to be eutectic.

“Eutectic alloys are the mixes of metals that produce the lowest melting point at a particular combination,” said Tang. “For instance, if we combine bismuth at 57% and tin at 43% they melt at 139^oC. But by themselves, both bismuth and tin have melting points above 200^oC.”

Kalantar-Zadeh said the specific mix ratio of eutectic substances produces the maximum natural chaos at the nano-level, which in turn brings the melting point down. The process can also work the other way. Eutectic metal substances already in liquid form can solidify at a single temperature below the usual freezing point of each metal.

“This maximum chaos helps, when we solidify the liquid metals, to naturally produce so many defects in the material that the ‘catalytic’ activity is significantly enhanced,” Kalantar-Zadeh said.

Liquid metals and the environment

Liquid metal alloys can be used to remove or neutralize pollutants in the environment as well as capturing the carbon in CO2 emissions. Tin, gallium and bismuth when in liquid form can be used as electrodes to convert carbon dioxide into useful byproducts. Another environmental application is that after heating the liquid metals to make oxides, the substances can also be used to absorb energy from light, which enables them to break down contaminants in water.

What makes liquid metals an attractive option in solving environmental problems is the fact they can be cheaply produced using low energy and in a low-tech environment.

“Metals such as tin and bismuth are accessible to many people around the world,” said Kalantar-Zadeh. “People should just consider how easily, cheaply and with so little need for advanced technology that they can be processed and transformed into useful materials such as catalysts.

“Additionally, playing with liquid metals is fun. While the most famous liquid metal – mercury – is well known to be hazardous, a liquid metal like gallium is completely non-toxic, and meltable at or near room temperature, where we can use it to transform one material to another at very low input energies. Liquid metals could solve lots of problems that we as humans are grappling with these days.”

Reference

Tang et al. (2019). Advantages of eutectic alloys for creating catalysts in the realm of nanotechnology-enabled metallurgy. Nature Communications. DOI: https://doi.org/10.1038/s41467-019-12615-6

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