APS: Nanotubes as filters
I just got out of a pretty cool talk about filtering water with carbon nanotubes. Apparently because the walls of the tubes are so smooth, water molecules can flow super fast through them. On top of that, the rims of the tubes are charged and can therefore reject unwanted ions.
Olgica Bakajin of Lawrence Livermore National Laboratory had some impressive results on display. She fashioned crude filters by growing carbon nanotubes on a silicon surface. She embedded the tubes in silicon nitride and shaved down the compound until a few of the tubes' tops were open. As the image on the right reveals, it’s not the prettiest technique (only those tubes in yellow are actually open). But it works! Her filter allows lots of water through and rejects ions at rates compatible with commercial products.
The immediate application would be for water softening, a process by which ions are removed from water in order to prevent crusty build-up (as an American living in the UK I can attest that there’s plenty of room for improvement on that front). The good thing about the tubes is that they would be higher-throughput and thus more energy efficient than commercial products. And Bakajin tells me that if they can get the diameter a little smaller, they might even be able to desalinate seawater...
credit: Y. Wang/LLNL
