Among graphene's long list of superpowers, filtering water may be one of the most directly beneficial. Now a team of Australian scientists has demonstrated how effective a specially-designed form of graphene can be at purifying water with a pretty challenging test: the filter made water from Sydney Harbour safe to drink in one step.
As well as being extremely strong and an excellent conductor of heat and electricity, graphene has proven itself to be an effective water filter. These devices could take the form of biofilm sheets floating on top of dirty or salty water, which absorb and purify the water. Other methods include a graphene-oxide membrane that can filter even the smallest salts out of water without impeding the flow.
The newest graphene water filter system was made using a form of the material dubbed "Graphair," which was developed last year by a team at the CSIRO. Graphene is normally created using an energy-intensive process of chemical vapor deposition onto metal substrates, but Graphair is made from soybean oil, an inexpensive and renewable material.
In the new study, the team coated a commercial water filter with a thin film of Graphair, which contains microscopic nano-channels that block contaminants while allowing water to pass through. To really put it to the test, they ran samples of water from the heavily-polluted Sydney Harbour through these filters, some with a layer of Graphair and some without. After just one pass, the Graphair filters had purified the water to a drinkable standard.
"In Graphair we've found a perfect filter for water purification," says Dong Han Seo, lead author on a paper describing the project. "It can replace the complex, time consuming and multi-stage processes currently needed with a single step. All that's needed is heat, our graphene, a membrane filter and a small water pump."
The Graphair filters also managed to keep their filtration rate higher for longer. One of the main problems with regular filters is that the unwanted material tends to build up on the membrane, eventually slowing down the rate that water can pass through. In these tests, the team found that after 72 hours, filters in the control group were only half as effective as they'd been initially. The Graphair filters didn't have this problem, with membranes 4 cm2 (0.6 in2) in size processing about 0.5 liters (17 oz) per day.
The researchers say they hope to start field trials of the Graphair water filters in developing countries next year. In the long run, the technology could be scaled up to clean a home or town's water supply, and may eventually be used to filter seawater and industrial wastewater on a large scale.
The study was published in the journal Nature Communications. The researchers describe their work in the video below.
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