Less than 1 percent of Earth’s water is drinkable. Removing salt and other minerals from our biggest available source of water—seawater—may help satisfy a growing global population thirsty for fresh water for drinking, farming, transportation, heating, cooling and industry. But desalination is an energy-intensive process, which concerns those wanting to expand its application.
Now, a team of experimentalists led by the Department of Energy’s Oak Ridge National Laboratory has demonstrated an energy-efficient desalination technology that uses a porous membrane made of strong, slim graphene—a carbon honeycomb one atom thick. The results are published in the March 23 advance online issue of Nature Nanotechnology.
“Our work is a proof of principle that demonstrates how you can desalinate saltwater using free-standing, porous graphene,” said Shannon Mark Mahurin of ORNL’s Chemical Sciences Division, who co-led the study with Ivan Vlassiouk in ORNL’s Energy and Transportation Science Division.
“It’s a huge advance,” said Vlassiouk, pointing out a wealth of water travels through the porous graphene membrane. “The flux through the current graphene membranes was at least an order of magnitude higher than [that through] state-of-the-art reverse osmosis polymeric membranes.”
Current methods for purifying water include distillation and reverse osmosis. Distillation, or heating a mixture to extract volatile components that condense, requires a significant amount of energy. Reverse osmosis, a more energy-efficient process that nonetheless requires a fair amount of energy, is the basis for the ORNL technology.
Making pores in the graphene is key. Without these holes, water cannot travel from one side of the membrane to the other. The water molecules are simply too big to fit through graphene’s fine mesh. But poke holes in the mesh that are just the right size, and water molecules can penetrate. Salt ions, in contrast, are larger than water molecules and cannot cross the membrane. The porous membrane allows osmosis, or passage of a fluid through a semipermeable membrane into a solution in which the solvent is more concentrated.
“If you have saltwater on one side of a porous membrane and freshwater on the other, an osmotic pressure tends to bring the water back to the saltwater side. But if you overcome that, and you reverse that, and you push the water from the saltwater side to the freshwater side—that’s the reverse osmosis process,” Mahurin explained.
Today reverse-osmosis filters are typically polymers. A filter is thin and resides on a support. It takes significant pressure to push water from the saltwater side to the freshwater side. “If you can make the membrane more porous and thinner, you can increase the flux through the membrane and reduce the pressure requirements, within limits,” Mahurin said. “That all serves to reduce the amount of energy that it takes to drive the process.”
Graphene to the rescue
Graphene is only one-atom thick, yet flexible and strong. Its mechanical and chemical stabilities make it promising in membranes for separations. A porous graphene membrane could be more permeable than a polymer membrane, so separated water would drive faster through the membrane under the same conditions, the scientists reasoned. “If we can use this single layer of graphene, we could then increase the flux and reduce the membrane area to accomplish that same purification process,” Mahurin said.
The Latest on: Desalination
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The Latest on: Desalination
- MRPL to commission seawater desalination plant in Q3 of 2020-21on July 6, 2019 at 5:19 am
Mangalore Refinery and Petrochemicals Ltd (MRPL), which is setting up a seawater desalination plant at an estimated cost of ₹620 crore, is planning to commission it in the third quarter of 2020-21. ... […]
- Tamil Nadu plans new desalination plant for thermal units in north Chennaion July 4, 2019 at 11:45 pm
Chennai already has two desalination plants at Minjur and Nemili, each with a capacity of 100 million litres p...Read More Some years ago, the Union ministry of environment, forest and climate ... […]
- Insects inspire greener, cheaper membranes for desalinationon July 1, 2019 at 7:40 am
A new membrane made from water-wet materials has specially designed gas-entrapping pores that allow it to simultaneously separate hot, salty from cool, pure water while facilitating the transfer ... […]
- Desalination plant to come up at Tamil Nadu's Marakkanamon June 30, 2019 at 6:03 pm
VILLUPURAM: Law minister C Ve Shanmugam on Sunday said the government was planning to set up a desalination plant in Marakkanam to supply drinking water to Villupuram. He said CM Edappadi K ... […]
- Desalination to solve water problemon June 30, 2019 at 9:28 am
CEBU, Philippines — A seawater desalination plant is seen to soon address the water shortage problem of Lapu-Lapu City. Congresswoman Paz Radaza, of the city’s lone district, said during her last ... […]
- Chennai water crisis: Are desalination plants the answer?on June 28, 2019 at 2:49 am
Two desalination plants, set up in Minjur in north Chennai and Nemmeli on the East Coast Road, in 2010 and 2013, respectively, have ensured that Chennai gets an assured drinking water supply of 200 ... […]
- More desalination plants, desalters neededon June 27, 2019 at 2:57 pm
Since Oxnard and Ventura, along with hundreds of other California cities, are being forced to grow their populations by 20 to 30 percent each, over the next 10 years, by idiots in Sacramento ... […]
- Edappadi K Palaniswami lays foundation for desalination planton June 27, 2019 at 11:43 am
Tamil Nadu chief minister Edappadi K Palaniswami on Thursday inaugurated a project for expanding the capacity of the Nemmeli desalination plant, as the state government seeks to ease Chennai’s chronic ... […]
- TN CM lays foundation stone for seawater desalination planton June 27, 2019 at 8:43 am
The Tamil Nadu Chief Minister Edappadi K Palaniswami laid the foundation stone for a ₹1,259-crore seawater desalination plant at Nemmeli on the East Coast Road. The 150 million litres per day (MLD) ... […]
- Desalination Is Booming as Cities Run out of Wateron June 27, 2019 at 6:00 am
This story originally appeared on Yale Environment 360 and is part of the Climate Desk collaboration. Some 30 miles north of San Diego, along the Pacific Coast, sits the Claude “Bud” Lewis Carlsbad ... […]
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