This shows a liquid metal droplet with flakes of aluminium oxide compounds that were grown on its surface. Each 0.03mm flake is made up of about 20,000 nano-sheets stacked together. Image: RMIT University.
This shows a liquid metal droplet with flakes of aluminium oxide compounds that were grown on its surface. Each 0.03mm flake is made up of about 20,000 nano-sheets stacked together. Image: RMIT University.

Researchers from RMIT University and the University of New South Wales (UNSW), both in Australia, have designed a rapid nano-filter that can clean dirty water over 100 times faster than current technology. Simple to make and simple to scale up, the technology harnesses naturally occurring nanostructures that grow on liquid metals.

The researchers have shown that this innovation can filter both heavy metals and oils from water at extraordinary speed. They describe the nano-filter in a paper in Advanced Functional Materials.

According to RMIT researcher Ali Zavabeti, water contamination remains a significant challenge globally – one in nine people have no clean water close to home. "Heavy metal contamination causes serious health problems and children are particularly vulnerable," he said. "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. 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 also 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 Kourosh Kalantar-Zadeh, professor of chemical engineering at UNSW, said that the liquid metal chemistry used in the process allows different nanostructures to be grown. These comprise the atomically thin sheets used for the nano-filter and nano-fibrous structures.

"Growing these materials conventionally is power intensive, requires high temperatures, extensive processing times and uses toxic metals," he explained. "Liquid metal chemistry avoids all these issues so it's an outstanding alternative."

The ground-breaking technology is sustainable, environmentally-friendly, scalable and low-cost. The researchers start by combining gallium-based liquid metals with aluminium to create an alloy. When this alloy is exposed to water, nano-thin sheets of aluminium oxide compounds grow naturally on its surface.

These atomically thin layers – 100,000 times thinner than a human hair – restack in a wrinkled fashion, making them highly porous. This porosity allows water to pass rapidly through the layers while the aluminium oxide compounds absorb the contaminants.

Experiments showed that this nano-filter could efficiently remove lead from water that had been contaminated at over 13 times safe drinking levels, and was also highly effective at 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-fibers. These different shapes have different characteristics – the ultra-thin sheets used in the nano-filter experiments have high mechanical stiffness, while the nano-fibers are highly translucent.

This ability to grow materials with different characteristics offers opportunities to tailor the shapes to enhance different properties for applications in electronics, membranes, optics and catalysis.

This story is adapted from material from RMIT University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.