Graphene oxide sheets to transform dirty water into drinking water

Graphene oxide has been hailed as a veritable wonder material; when incorporated into nanocellulose 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.

“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,” said Srikanth Singamaneni, associate professor of mechanical engineering and materials science at the School of Engineering & Applied Science.

The new approach combines bacteria-produced cellulose and graphene oxide to form a bi-layered biofoam. A paper detailing the research is available online in Advanced Materials.

“The process is extremely simple,” Singamaneni said. “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.

“The design of the material is novel here,” 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 — but the heat dissipation to the bulk water underneath is minimized by the pristine nanocellulose 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 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. In the same way an oyster makes a pearl, the bacteria forms layers of nanocellulose 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 new biofoam is also extremely light and inexpensive to make, making it a viable tool for water purification and desalination.

“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 synthesized 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.

“The 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. We will also explore other applications for these novel structures.”

Singamaneni may be reached for interviews at singamaneni@wustl.edu; Biswas at pbiswas@wustl.edu.

 

Source: https://source.wustl.edu/2016/07/dirty-to-drinkable/

Lockheed Martin Says This Desalination Technology Is An Industry Game-Changer

Lockheed Martin Says This Desalination Technology Is An Industry Game-Changer

Workers stand near pressure vessels at Britain’s first-ever mainland desalination plant, known as the Thames Gateway Water Treatment.

The latest technology for removing salt from seawater, developed by Lockheed Martin, will be a game-changer for the industry, according to Ray O. Johnson, senior vice president and chief technology officer of the jet and weapons manufacturer.

Desalination technology is used in regions of the world, particularly developing countries, where fresh water is not available. Water from oceans or rivers is diverted into treatment plants where the salt is removed and clean drinking water is produced through a process called reverse osmosis.

Imagine a tank with seawater on one side and pure water on the other, separated by a filter with billions of tiny holes. Lots of pressure on the salty side pushes water through faster than the salt, so fresh water comes out the other end.

The problem is that current filters use plastic polymers that use an immense amount of energy (800 to 1,000 pounds per square inch of pressure) to push water through.

Lockheed has developed a special material that doesn’t need as much energy to drag water through the filter.

Graphene is a substance made of pure carbon. Carbon atoms are arranged in a regular hexagonal or honeycomb pattern in a one-atom thick sheet.

This special material is a film of a special structure of carbon, a honeycomb lattice called graphene.

“Graphene is pure carbon that is made in a hot oven on top of a copper sheet
in a vacuum,” John Stetson, the chief technologist at Lockheed for this initiative explained to Business Insider. “Methane gas is put into the vacuum and the methane changes
into a single film of carbon atoms all linked together tightly like chickenwire (at the atomic level) 1,000 times stronger than steel and tolerant of temperature, pressure and pH.”

The sheet is dotted with holes that are one nanometer or less. These holes between carbon atoms trap the salt and other impurities.

Graphene researchers won the Nobel Prize in Physics in 2010 for developing the wonder-material.

In addition, the film is super thin — just a single atom thick — so that the water simply “pops through the very, very small holes that we make in the graphene and leaves the salt behind,” said Stetson.

Lockheed anticipates that their filters will be able to provide clean drinking water “at a fraction of the cost of industry-standard reverse osmosis systems,” their press release says. Water-poor regions of the world will be the first to benefit.

The perforated graphene is aptly called Perforene. Lockheed has the U.S. Patent on this technology and is currently pumping out “pretty big quantities of it” at Lockheed’s advanced technology center in Palo Alto, California, according to Stetson.

The Perforene has a smoky grey-color film that is translucent, even though its carbon, because it is so thin. It’s also about 1,000 times stronger than steel, but still has a permeability that is about 100 times greater than the best competitive membrane out in the market, said Stetson.

Perforene isn’t a game-changer, yet. Lockheed is still in the prototype stage. One challenge is figuring out how to scale up production. Graphene is cheap but it’s very delicate because of its thinness, also making it difficult to transfer.

Stetson says Lockheed is targeting to have a prototype to test in a reverse osmosis plant by 2014 or 2015, where they would simply be able to “plug in” the Perforene to replace the existing filter.

The great news is that this technology is not just limited to desalination plants. It can potentially be used for pharmaceutical filtration, dialysis, and gas separation, to a name a few other uses.

The possibilities are endless.