Can engineered carbon nanotubes help to avert our water crisis?

March 17, 2015, Elsevier

Carbon nanotube (CNT) membranes have a bright future in addressing the world's growing need to purify water from the sea, researchers say in a study published in the journal Desalination.

"Currently, about 400 million people are using desalinated water and it has been projected that by 2025, 14 percent of the global population will be forced to use sea water," said Md. Eaqub Ali, from the University of Malaya's Nanotechnology and Catalysis Research Center in Kuala Lumpur, Malaysia. He says engineered CNT membranes have the potential to tackle the current and future challenges in water purification.

For efforts to review the state of carbon nanotube technology and push the field forward, Ali and his colleagues have been selected for an Elsevier Atlas award.

Desalination plants already provide much of the water used by people in many parts of the world, especially in Israel, Saudi Arabia, and Australia. Climate change is only increasing the demand for as greater evaporation and rising seas further limit freshwater supplies for a growing world population. But current methods to desalinate water come at a very high cost in terms of energy, which means more greenhouse gases and more global warming.

Existing desalination plants rely on reverse osmosis, vacuum distillation, or a combination of the two. But those methods are energy intensive and costly.

Carbon nanotubes are tiny hexagonal tubes, made by rolling sheets of graphene, said Rasel Das, first author of the paper. They require little energy and can be designed to specifically reject or remove not only salt, but also common pollutants.

"The hollow pores of the CNTs are extremely, extremely tiny," Ali said. "However, because of their amazing chemical and physical properties, they allow frictionless passes of water through the pores, but reject most salts, ions, and pollutants, giving us purified water, probably in its best form."

That frictionless property is also what gives CNTs the potential to purify water with so little energy. And carbon nanotube membranes come with other perks, Das added, including self-cleaning properties.

"What makes CNTs special is that they have cytotoxic properties," he said. That means that the membranes naturally kill microbes that might otherwise foul up their surfaces. As a result, membranes have the potential to last longer and may be reusable.

There are hurdles yet to overcome, co-author of the paper Sharifah Bee Abd Hamid said. CNT membranes are now costly to produce, especially for large-scale uses. Research is also needed to produce the membranes with pores of a more uniform distribution and size.

"Most progress in desalination research is focused on demonstrating [the capability of CNT membranes] at a small scale," she said.

For larger scale operations, work is needed to produce CNT membranes on thin films or fiber cloth composites. Getting the membranes ready for use will require effort on material design, operational requirements, and more.

If someday, these membranes can be put to use in water-filtering pitchers or bottles, "to directly treat salty water at point of use," Hamid says, "it is a dream come true for many."

The Editor-in-Chief of Desalination, Nidal Hilal, said about the research, "The available supplies of water are decreasing due to increased population growth, low precipitation, competing demands from industry and more stringent health based regulations for agricultural and urban development. We have to seek alternative sources of water such as seawater, storm water, wastewater, and industrial wastewater. Membrane filtration is considered among the most promising and widely used processes for water treatment and desalination...Carbon nanotubes (CNT) have shown great potential in , wastewater treatment and desalination as they have many attractive key physicochemical properties with the ability to be functionalized to enhance their affinity and selectivity."

Explore further: Using solar energy to improve desalination process

More information: "Carbon nanotube membranes for water purification: A bright future in water desalination." www.sciencedirect.com/science/ … ii/S0011916413006127

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gkam
not rated yet Mar 17, 2015
Good stuff. But we must be careful regarding the use of carbon fibers. They are sharp and penetrate tissue and cells, can migrate through the body. Graphene sheets are extremely sharp.

I will go out on a limb and predict we may have in the next five years a sudden realization of the nature of these materials when a car or boat or bus or aircraft of carbon fiber burns and the resulting carbon-rich smoke, loaded with tiny needles of graphite, take out the local electrical power system.
tadchem
not rated yet Mar 17, 2015
Thermodynamics tells us that water purification will erquire a specific amount of energy per unit purified, with an accompanying reduction in entropy of the water/solute system. The nanotubes can only act as catalysts, reducing the amount the total ennergy of the system needs to be raised to get it over the thermodynamic hump between raw materials and products. The real gains will be realized by improving efficiency of the syste - i.e. minimization of lost heat.
Maritxu
1 / 5 (1) Mar 18, 2015
It's very bad that we investigate these C nanotubes since tens of years and we still don't know for what we could use them in real life... And the same happens now with the graphene, much fuzz the last few years, and no real applications. Big money invested and no real results for clear applications shown. Thank you, European Research Council, for investing tones of our money on useless projects, such as graphene and the Brain(Waste)-project! We like to see our money wasted! Keep on choosing such "good" and "useful" projects to be financed from our money!

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