New nanofilter rapidly cleans dirty water

Australian researchers have designed a nanofilter that can clean dirty water over 100 times faster than current technology, filtering both heavy metals and oils at an impressive speed.

Simple to make and to scale up, the technology harnesses naturally occurring nanostructures that grow on liquid metals. It has been described in the journal Advanced Functional Materials.

Led by RMIT University, the research team began by creating an alloy by combining gallium-based liquid metals with aluminium. When this alloy is exposed to water, nanothin 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, making them highly porous. This enables water to pass through rapidly while the aluminium oxide compound absorbs the contaminants.

Experiments showed the nanofilter 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 re-used for each new batch of nanostructures.

Microscope image of nanosheets, magnified over 11,900 times. Image credit: RMIT University.

“Our new nanofilter is sustainable, environmentally friendly, scalable and low cost,” said RMIT researcher Dr 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 already shown the materials we used are effective in absorbing contaminants like mercury, sulfates and phosphates.”

Project leader Professor Kourosh Kalantar-zadeh, an Honorary Professor at RMIT and Professor of Chemical Engineering at UNSW, said the liquid metal chemistry used in the process enables differently shaped nanostructures to be grown, either as the atomically thin sheets used for the nanofilter or as nanofibrous structures.

“Growing these materials conventionally is power intensive, requires high temperatures, extensive processing times and uses toxic metals,” he said.

“Liquid metal chemistry avoids all these issues so it’s an outstanding alternative.”

A liquid metal droplet with flakes of aluminium oxide compounds grown on its surface. Each 0.03 mm flake is made up of about 20,000 nanosheets stacked together. Image credit: RMIT University.

These different shapes have different characteristics — the ultrathin sheets used in the nanofilter experiments have high mechanical stiffness, while the nanofibres 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.

“The technique is potentially of significant industrial value, since it can be readily upscaled, the liquid metal can be re-used and the process requires only short reaction times and low temperatures,” Dr Zavabeti said.

“With further development and commercial support, this new nanofilter could be a cheap and ultrafast solution to the problem of dirty water.”

Top image credit: ©stock.adobe.com/au/Chepko Danil