A liquid metal droplet with flakes of aluminium oxide compounds grown on its surface. Each 0.03mm flake is made up of about 20,000 nano-sheets stacked together. (Image courtesy RMIT University.)
Access to clean, uncontaminated water is one of the biggest global challenges, and is particularly important in developing nations where as few as one in nine people have clean water located close to their home.
"Heavy metal contamination causes serious health problems and children are particularly vulnerable," said Ali Zavabeti Zavabeti, a researcher at RMIT University in Australia.
In an attempt to find a solution to contaminated water, a team of Australian researchers have designed a rapid nano-filter that can clean dirty water over 100 times faster than current technology.
The technology harnesses naturally occurring nano-structures that grow on liquid metals, which means it is simple to make and simple to scale up.
The researchers behind the innovation are from RMIT University and University of New South Wales (UNSW). Their research shows the nano-filter can filter both heavy metals and oils from water at an extraordinary speed.
"Our new nano-filter is sustainable, environmentally-friendly, scalable and low cost. We've shown it works to remove lead and oil from water but we also know it has potential to target other common contaminants,” said Zavabeti. "Previous research has already shown the materials we used are effective in absorbing contaminants like mercury, sulfates and phosphates. With further development and commercial support, this new nano-filter could be a cheap and ultra-fast solution to the problem of dirty water."
The liquid metal chemistry process developed by the researchers has potential applications across a range of industries including electronics, membranes, optics and catalysis.
"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," Zavabeti said.
Project leader Professor Kourosh Kalantar-zadeh, professor of chemical engineering at UNSW, said the liquid metal chemistry used in the process enabled differently shaped nano-structures to be grown, either as the atomically thin sheets used for the nano-filter or as nano-fibrous structures.
"Growing these materials conventionally is power intensive, requires high temperatures, extensive processing times and uses toxic metals. Liquid metal chemistry avoids all these issues so it's an outstanding alternative," Kalantar-zadeh added.
Atomically Thin Layers of Aluminium Oxide Filter Out Contaminants
This nano-filter technology is sustainable, environmentally-friendly, scalable and low-cost.
According to the researchers, they created an alloy by combining gallium-based liquid metals with aluminium. When this alloy is exposed to water, nano-thin sheets of aluminium oxide compounds grow naturally on the surface.
These atomically thin layers—100,000 times thinner than a human hair—restack in a wrinkled fashion, which makes them highly porous. This enables water to pass through rapidly while the aluminium oxide compounds absorb the contaminants.
Experiments showed the nano-filter made of stacked atomically thin sheets was efficient at removing lead from water that had been contaminated at over 13 times safe drinking levels, and was highly effective in separating oil from water.
The process generates no waste and requires just aluminium and water, with the liquid metals reused for each new batch of nano-structures.
The method developed by the researchers can be used to grow nano-structured materials as ultra-thin sheets and also as nano-fibres.
These different shapes have different characteristics - the ultra-thin sheets used in the nano-filter experiments have high mechanical stiffness, while the nano-fibres are highly translucent.
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.
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Source: RMIT University