Australian researchers have designed a rapid nanofilter that can clean dirty water over 100 times faster than current technology. The technology is said to be simple to make and simple to scale up, as it harnesses naturally occurring nanostructures that grow on liquid metals.
A liquid metal droplet with flakes of aluminium oxide compounds grown on its surface. Each 0.03mm flake is made up of around 20,000 nanosheets stacked together (image: RMIT University)
RMIT researcher Dr Ali Zavabeti said: "Heavy metal contamination causes serious health problems and children are particularly vulnerable. Our new nano-filter is sustainable, environmentally-friendly, scalable and low cost.”
He added: "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 nanofilter could be a cheap and ultra-fast solution to the problem of dirty water."
Project leader Professor Kourosh Kalantar-zadeh, Honorary Professor at RMIT, Australian Research Council Laureate Fellow and Professor of Chemical Engineering at UNSW, said the liquid metal chemistry used in the process enabled differently shaped nanostructures to be grown, either as the atomically thin sheets used for the nanofilter or as nanofibrous structures, saying: "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."
The researchers 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, making them highly porous. This enables water to pass through rapidly while the aluminium oxide compounds absorbs the contaminants.
Microscope image of nano-sheets, magnified over 11,900 times (Image: RMIT University)
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 reused for each new batch of nanostructures.