Tech + Engineering

09
Sep

Wonder Material Graphyne Could Make Desalination Cheaper

A few years ago, two physicists won the Nobel Prize, in part, by sticking Scotch tape to a pencil lead and then pulling it off. That simple experiment produced a remarkable two-dimensional material—graphene—and the pair’s study of its properties won them international acclaim. Graphene is super strong, flexible, and an astonishingly good conductor of electricity. The material’s properties stem from it’s structure, which is a single layer of carbon atoms connected by double bonds in a repeating hexagonal pattern.

But graphene is just one form of carbon among many. Another is graphyne, which adds triple bonds to the mix, the number of which depends on the species. (Unlike graphene, there are many different types of graphyne.) Graphyne is an excellent electrical conductor, just like its double-bonded cousin, but computer models suggest that it differs from graphene by only allowing electrons to move in one direction, a property that’s much desired by chip designers.

But wait, there’s more! A new study from Nanjing University of Aeronautics and Astronautics in China suggests that graphyne could be used as an efficient filter for desalination. Most current desalination plants rely on reverse osmosis, where salt water is forced through a membrane. The membrane blocks salt ions but allows water molecules to slip through. To work, though, the salt water must be pressurized, making the process is energy intensive and expensive. One way to lower costs is to use a more efficient filter.

The Physics arXiv Blog:

Graphyne is interesting because these double and triple bonds create holes between the carbon atoms that are large enough for water molecules to pass through. However, these holes are not big enough for sodium and chloride ions, which are larger because they attract a shell of water molecules since they are charged.

desalination plant2
Current membranes used in desalination require lots of energy to force water through.

Graphyne can form in several configurations known as α-graphyne, β-graphyne, graphyne-3 and so on. Wanlin and co have created a computer simulation of the way that these membranes allow water molecules to pass through while sieving the various types of ions found in seawater.

They predict that the energy requirements to get water through the membrane are much lower than with existing materials.

Unfortunately, we haven’t yet made graphyne in large enough sheets, nor has anyone made α-graphyne, β-graphyne, or graphyne-3, the sorts tested in the simulation. But labs are working on it, and in the meantime, that other type of carbon sheet may fill the gap. Lockheed Martin has developed a way to punch holes in graphene’s hexagonal lattice, which mimic graphyne’s natural gaps.

For more on graphene, watch the segment from “Making Stuff Smaller.” It starts at 18:30.