A nanofibre cloth could help drought-hit communities capture drinking water from the air.
Fog nets usually consist of a sheet of polythene mesh strung between two poles. Passing water vapour condenses on the small fibres and trickles down into collection bottles below.
However, the yield of these nets is often limited and the water only flows on foggy days. The technology is also restricted to mountainous regions where warm, wet air arriving from the coast is forced up steep slopes, where it cools and condenses as fog.
Shing-Chung Josh Wong at the University of Akron in Ohio, US and his team created a new material that they believe will be a large improvement. They used electrospun polymers – a technique which allowed them to create nanoscale fibres. These are tangled around fragments of expanded graphite, like spaghetti around meatballs. The fibres provide a large surface area for droplets to condense onto, and the graphite encourages the water to drip out of the material when it is squeezed or heated.
Wong says that harvesters made with these nanofibres could yield up to 180 litres of water per square metre every day. In comparison, a commercial system currently in use in Morocco only produces around 30 litres per square metre per day.
As well as squeezing water from the air, the nanofibres also filter out dirt and bacteria, meaning the water is safe to drink. Although the system can work passively, Wong envisions using a small battery to cool an element attached to the material. This would mean the harvester could operate beyond the range of typical fog nets – even in deserts.
“There is always some humidity in the atmosphere. Where you see cloud, that means there is water,” says Wong. He says to operate the collector it would only need to be 10 degrees cooler than the surrounding environment. With the advent of lithium ion batteries, “we can put the whole thing into a backpack.”
The findings were presented at the National Meeting & Exposition of the American Chemical Society in Boston, Massachusetts.