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Bi-layered biofoam turns dirty water into drinking water

A team of engineers at Washington University in St Louis has found a way to use graphene oxide sheets to transform dirty water into drinking water.

Srikanth Singamaneni, associate professor of mechanical engineering and materials science at the university’s School of Engineering & Applied Science, said: “We hope that for countries where there is ample sunlight, such as India, you’ll be able to take some dirty water, evaporate it using our material, and collect fresh water.”

The new approach combines bacteria-produced cellulose and graphene oxide to form a bi-layered biofoam.

Singamaneni said. “You have a bi-layered structure with light-absorbing graphene oxide filled nanocellulose at the top and pristine nanocellulose at the bottom. When you suspend this entire thing on water, the water is actually able to reach the top surface where evaporation happens.”

Light radiates on top of it, and it converts into heat because of the graphene oxide. The heat dissipation to the bulk water underneath is minimised by the pristine nanocellulose layer.

The process in which the bi-layered biofoam is actually formed is also novel, said Singamaneni. In the same way an oyster makes a pearl, the bacteria form layers of nanocellulose fibres in which the graphene oxide flakes get embedded.

Graphene oxide flakes were added to the medium itself while the bacteria for the cellulosed was being cultured. The graphene oxide becomes embedded as the bacteria produces the cellulose. At a certain point along the process, the medium with the graphene oxide is removed and fresh medium is reintroduced to produce the next layer of foam.

“Cellulose can be produced on a massive scale,” Singamaneni said, “and graphene oxide is extremely cheap — people can produce tons, truly tons, of it. Both materials going into this are highly scalable. So one can imagine making huge sheets of the biofoam.”

“The properties of this foam material that we synthesised has characteristics that enhances solar energy harvesting. Thus, it is more effective in cleaning up water,” said Pratim Biswas, the Lucy and Stanley Lopata professor and chair of the Department of Energy, Environmental and Chemical Engineering.

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