Nanotubes creating fresh water

Nanotubes creating fresh water


Imagine a bunch of molecule-herders riding to the rescue of the world’s water crisis.

Researchers at California’s Lawrence Livermore National Laboratory are working on a project that would do just that, using carbon nanotube-based membranes to remove salt from the world’s ocean and seawater and make the result OK to drink for people and animals.

That process as it exists now is called desalination, and it is horribly expensive. The Lawrence Livermore method, on the other hand, would cut the cost of such desalination by up to 75 percent, the scientists say.

The method consists of thousands of nanotubes acting as the herd dogs or ranch hands, sorting the molecules of the water passing through them by size. The result is salt and water but not both.

The nanotubes are beyond tiny. They are sheets of carbon atoms that are rolled so tightly together that the diameter of one sheet is the size of seven water molecules. Despite their relative lack of size, however, they do the job of sorting water from saltwater better than methods being employed now and at a higher rate of speed as well.

The nanotubes are at the center of a silicon wafer that is the size of a 25-cent coin, or quarter. The scientists coated each wafer with a metal nanoparticle catalyst, which fosters the growth of the nanotubes, and then filled in any gaps with silicon nitride, which seals off any spillage.

The result is quite effective, the scientists say, leaving salt behind to be collected while allowing the rest of the molecules (namely, fresh water) to flow through and into container tanks.

The going prediction for when these membranes will be commonly available is anywhere from 5 to 10 years, the scientists say. For current needs, the membranes will have to be a whole lot bigger, perhaps as a giant field of smaller ones put together or maybe as one large one. Either way, the number of nanotubes in such a device would be in the millions.

The scientists hope to one day use similar membranes to separate various gas molecules as well. One such use would be to remove carbon dioxide from exhaust, eliminating harmful emissions.