Graphene-based sieve turns seawater into drinking water

[nitpicker]

http://www.bbc.com/news/science-environment-39482342

Graphene-based sieve turns seawater into drinking water

By Paul Rincon
Science editor, BBC News website

3 April 2017

From the section Science & Environment

A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes.

It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide.
(snip)

On the other hand, said Dr Nair, "graphene oxide can be produced by simple oxidation in the lab". He told BBC News: "As an ink or solution, we can compose it on a substrate or porous material. Then we can use it as a membrane. "In terms of scalability and the cost of the material, graphene oxide has a potential advantage over single-layered graphene."

Of the single-layer graphene he added: "To make it permeable, you need to drill small holes in the membrane. But if the hole size is larger than one nanometre, the salts go through that hole. You have to make a membrane with a very uniform less-than-one-nanometre hole size to make it useful for desalination. It is a really challenging job."

Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn't be used to filter out common salts, which require even smaller sieves.

Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules. Now, Dr Nair and colleagues demonstrated that placing walls made of epoxy resin (a substance used in coatings and glues) on either side of the graphene oxide membrane was sufficient to stop the expansion. Restricting the swelling in this way also allowed the scientists to tune the properties of the membrane, letting through less or more common salt for example.
(snip)

[Warpy]

1. If this pans out and the manufacture is cheap and easy

this could be a real game changer not only in the developing world, but in places in the west where so much of the water is brackish and undrinkable. Imagine if all water became potable water once filtered and Pasteurized.

[DetlefK]

2. With pores this fine, there would be no need for pasteurization.

1 nm? That's smaller than a bacterium, smaller than a virus. Hell, it's smaller than a prion!

[DetlefK]

3. How they did it:

http://www.nature.com/nnano/journal/vaop/ncurrent/full/nnano.2017.21.html

They used a bulk piece of Graphene-Oxide, which consists of stacked molecular sheets. They stored it in humid air. The Graphene-Oxide absorbed some water and started to swell. The distance between the layers increased. Then the scientists glued the piece into a frame, to prevent further swelling, and put it into water.

The distance between the layers is big enough to let water-molecules through. But salt-ions have a shell of water-molecules that accompanies them, a so-called "hydrate-shell". This shell makes the ion to big to pass through the space between the layers.

[democrank]

4. So many people could benefit from this.

According to this article, the UN claims 14% of the world's people will face water scarcity by 2025. The researchers must be very hopeful.

Thanks for posting this.

[Beakybird]

5. Can they industrialized this?

I'll take it with a grain of salt.

[pscot]

6. That's always the key question

Will it scale up, and when?

[hunter]

7. The only thing that really matters is energy efficiency. Modern desalinization technology...

... is closing in on maximum possible efficiency.

It doesn't seem likely this technology could catch up with and overtake existing reverse osmosis systems, or speculative forward osmosis systems.

These membranes might prove useful in the manufacture of drugs and other chemicals, but I guess if you are a researcher seeking further funding and good press, that's not as sexy. Time for another feel-good-this-might-save-the-world story.

In any case, using fossil fuel energy to desalinate water is utter madness, especially in places where that water is used for front lawns and golf courses. It's simply making more mess for future generations to suffer. That's why I don't get exited about it. What's the point of extracting fresh water in one place if coal mines and fracking are contaminating the water in another place and greenhouse gasses are being released into the atmosphere? Furthermore, reverse osmosis filters only last a few years and then they are garbage.

Existing large scale desalinization plants are requiring 3 kilowatt/hours for every cubic meter (264 U.S. Gallons) of fresh water extracted.