Graphene oxide-based foam to clean dirty water

Researchers at Washington University have managed to use graphene oxide sheets to create a biofoam that can transform dirty water into drinking water. Their hope is that in countries where there is a lot of sunlight, it'll be possible to take dirty water, evaporate it using this material, and collect fresh water.

This new method combines bacteria-produced cellulose and graphene oxide to form a bi-layered biofoam. The production process is said to be extremely simple, and the nanoscale cellulose fiber network produced by bacteria has excellent ability to move the water from the bulk to the evaporative surface while minimizing the heat coming down. The material is a bi-layered structure with light-absorbing graphene oxide filled nanocellulose at the top and pristine nanocellulose at the bottom. When suspended this 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 minimized by the pristine nanocellulose layer. This way, heat is not wasted but confined to the top layer where the evaporation is actually happening.

The cellulose at the bottom of the bi-layered biofoam acts as a sponge, drawing water up to the graphene oxide where rapid evaporation occurs. The resulting fresh water can easily be collected from the top of the sheet.

The process in which the bi-layered biofoam is actually formed is also novel. According to the team, it works similarly to how an oyster makes a pearl - the bacteria forms layers of nanocellulose fibers in which the graphene oxide flakes get embedded.

While culturing the bacteria for the cellulose, the researchers added the graphene oxide flakes into the medium itself. At a certain point along the process, the medium is removed with the graphene oxide and a fresh medium is introduced. That produces the next layer of the foam. The interface is reportedly very strong and mechanically robust. The new biofoam is also extremely light and inexpensive to make, making it a viable tool for water purification and desalination.

The team added that their synthesis process also allows addition of other nanostructured materials to the foam that will increase the rate of destruction of the bacteria and other contaminants, and make it safe to drink.