Nanotechnology speeds desalination

From nanowerk:

Nanotechnology speeds desalination.

This story illustrates both the best and worst of near-term nanotech research and reporting. It’s a valuable result in a very important application:

“Current desalination methods force seawater through a filter using energies four times larger than necessary. Throughout the desalination process salt must be removed from one side of the filter to avoid the need to apply even larger energies.
“Using boron nitride nanotubes, and the same operating pressure as current desalination methods, we can achieve 100 percent salt rejection for concentrations twice that of seawater with water flowing four times faster, which means a much faster and more efficient desalination process.”

Here’s the abstract of the paper:

Salt Rejection and Water Transport Through Boron Nitride Nanotubes
Tamsyn A. Hilder *, Daniel Gordon, Shin-Ho Chung
Nanotube-based water-purification devices have the potential to transform the field of desalination and demineralization through their ability to remove salts and heavy metals without significantly affecting the fast flow of water molecules. Boron nitride nanotubes have shown superior water flow properties compared to carbon nanotubes, and are thus expected to provide a more efficient water purification device. Using molecular dynamics simulations it is shown that a (5, 5) boron nitride nanotube embedded in a silicon nitride membrane can, in principle, obtain 100% salt rejection at concentrations as high as 1 M owing to a high energy barrier while still allowing water molecules to flow at a rate as high as 10.7 water molecules per nanosecond (or 0.9268 L m-2 h-1). Furthermore, ions continue to be rejected under the influence of high hydrostatic pressures up to 612 MPa. When the nanotube radius is increased to 4.14 Å the tube becomes cation-selective, and at 5.52 Å the tube becomes anion-selective.

All good. What’s the “worst” part? It’s the title of the news story. The story itself indicates that the work is just theoretical, i.e. a simulation of water/ion flow in nanotubes. But just reading the title you’d get the idea that someone was ready to sell you a nanotube-based desalinator.  Or that at least one was in development. Or that at least the effect had been demonstrated in the lab.

Ah well.  At least we know that boron nitride nanotubes actually exist.

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