Graphene oxide has been hailed as a veritable wonder material; when incorporated into nano-cellulose foam, the lab-created substance is light, strong and flexible, conducting heat and electricity quickly and efficiently.
Now, 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, and it could be a global game-changer.
The new approach combines bacteria-produced cellulose and graphene oxide to form a bi-layered bio-foam.
A paper detailing the research is available online in Advanced Materials.
“The beauty is that the nanoscale cellulose fiber network produced by bacteria has excellent ability move the water from the bulk to the evaporative surface while minimizing the heat coming down, and the entire thing is produced in one shot.”
“You have a bi-layered structure with light-absorbing graphene oxide filled nano-cellulose at the top and pristine nano-cellulose 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 – but the heat dissipation to the bulk water underneath is minimized by the pristine nano-cellulose layer. You don’t want to waste the heat; you want to confine the heat to the top layer where the evaporation is actually happening.”
The cellulose at the bottom of the bi-layered bio-foam 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.
In the same way, an oyster makes a pearl, the bacteria forms layers of nano-cellulose fibers in which the graphene oxide flakes get embedded.
“While we are culturing the bacteria for the cellulose, we added the graphene oxide flakes into the medium itself,” said Qisheng Jiang, lead author of the paper and a graduate student in the Singamaneni lab.
“The graphene oxide becomes embedded as the bacteria produces the cellulose. At a certain point along the process, we stop, remove the medium with the graphene oxide and reintroduce fresh medium. That produces the next layer of our foam. The interface is very strong; mechanically, it is quite robust.”
“The properties of this foam material that we synthesized has characteristics that enhance 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.