Nanoporous graphene can strain salt molecules from water

Thirsty? No? You will be. It's just a matter of time. It's also just a matter of time until the expansion of humanity makes fresh water a more precious commodity than a new iPhone, but graphene sheets with lots of little holes in them could soon solve the problem by making fresh water from salt water with incredible efficiency.

Salt water is salt water because it has salt in it. That is to say, amongst all of those little molecules of H2O (water), you'll also find slightly larger molecules of NaCL (salt). The salt molecules cause lots of problems, not the least of which is that they render the water undrinkable by anyone except fish.

Of course, it's certainly possible to squeeze fresh water from salt water: you can do it through evaporation (which takes a lot of heat energy), or you can do it through reverse osmosis (which takes a lot of pressure energy). Either way, it's a very energy-intensive and inefficient process, which is why only a fraction of a percent of drinking water is currently produced this way. However, efficiency is becoming less and less relevant as demand for fresh water increases faster than we can keep up with, and those oceans out there are starting to look awfully refreshing.

Researchers at MIT have come up with a way to separate salt from fresh water by using a sort of a sieve made from single-atom-thick sheets of graphene that promises to be scads more efficient than any other process that exists. The concept is dead simple to understand: you've got a big flat sheet of graphite (made up of grids of carbon atoms), and the sheet has a lot of very small holes punched into it. These holes are just the right size to allow water molecules through, but salt molecules can't fit. So, if you fill a bucket of this stuff up with salt water, fresh water will drain out.

In practice, making a graphene bucket is not quite that simple: the sheets have to be stabilized somehow, the holes have to be drilled very carefully, and the edges of the holes have to be lined with other molecules to keep them from deteriorating. All of this is realistically possible to accomplish outside of a laboratory setting in the near future.

And just how good are these graphene sheets? A conventional reverse osmosis filter system can purify a few tenths of a liter of water per square centimeter of filter per day. A graphene sheet, on the other hand, can purify more than sixty liters per square centimeter of filter per day, which is an increase of several orders of magnitude, meaning that you can either get way more water, use way less energy, or both.

MIT, via Physorg

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