Clean environment possible through liquid metal

Washington: Forget other substances for solving environmental issues; researchers say liquid metal can easily do the job by capturing carbon and cleaning up pollutants. In a paper published today 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 of UNSW's School of Chemical Engineering said that "anyone with a shaker and a cook top 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 300oC on a cook top or in an oven," said Professor Kourosh Kalantar-Zadeh.

Professor 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. For instance, if we combine bismuth at 57 per cent and tin at 43 per cent they melt at 139oC. But by themselves, both bismuth and tin have melting points above 200oC," said Dr Tang.

Professor 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," Professor Kalantar-Zadeh said.

Here's how one can make a liquid metal catalyst. All you need is a eutectic alloy and water. The process is to take your eutectic metal alloy and place in a saucepan on a high flame, after the metal melts, carefully pour it into a bottle of water and tighten the cap.

Shake the liquid metal and water together to produce droplets of liquid metal in water. It will be similar to shaking oil and vinegar to produce droplets of oil in the vinegar. And at last, let the droplets solidify into a powder. This can now be used as a catalyst for the electrochemical conversion of CO2.

Liquid metal alloys can be used to remove or neutralise 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 by-products.

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. 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," said Professor Kalantar-Zadeh.