Fast nano-filter for removing metals

C&I Issue 8, 2018

Australian researchers say they have designed a nano-filter that can remove heavy metals and oils from water over 100 times faster than current technology.

Water contamination remains a significant challenge globally. Heavy metal contamination, in particular, causes serious health problems and children are particularly vulnerable. The researchers, from the RMIT University and the University of New South Wales, combined gallium-based liquid metals with aluminium to create an alloy. When exposed to water, thin sheets of aluminium oxide compounds grow naturally on the alloy surface. These atomically thin layers – 100,000 times thinner than a human hair – restack in a wrinkled fashion, making them highly porous. This allows water to pass through rapidly while the aluminium oxide compounds absorb the contaminants.

The team showed that the nano-filter removed lead efficiently from water contaminated at over 13 times safe drinking levels, and was highly effective in separating oil from water (Adv. Funct. Mater., doi: 10.1002/adfm.201804057).

‘Our new nano-filter is sustainable, environmentally-friendly, scalable and low cost,’ says RMIT researcher Ali Zavabeti. ‘We’ve shown it works to remove lead and oil from water but we also know it has potential to target other common contaminants. Previous research has shown the materials we used are effective in absorbing contaminants like mercury, sulfates and phosphates. The technique is potentially of significant industrial value, since it can be readily upscaled, the liquid metal can be reused, and the process requires only short reaction times and low temperatures.’

The method developed by the researchers can be used to grow nano-structured materials as ultra-thin sheets but also as nano-fibres. ‘Growing these materials conventionally is power intensive, requires high temperatures, extensive processing times and uses toxic metals,’ says Kourosh Kalantar-zadeh, professor of chemical engineering at UNSW. ‘Liquid metal chemistry avoids all these issues so it’s an outstanding alternative.’

The ability to grow materials with different characteristics offers opportunities to tailor the shapes to enhance their different properties for applications in electronics, membranes, optics and catalysis, says Zavabeti. The ultra-thin sheets used in the nano-filter experiments have high mechanical stiffness, while the nano-fibres are translucent.

Ken Ostrikov, a professor in the materials science and engineering department at QUT University in Brisbane, Australia, says the technology is ‘truly outstanding and promising’. The speed of the contaminant removal is impressive, and their design and use of liquid metal chemistry is novel, he notes.

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