Nanotube research could lead to point‑of‑use desalination

Membrane filtration using plasma-modified ultralong carbon nanotubes may lead to rechargeable point-of-use potable water purification appliances with superior desalination, disinfection and filtration properties according to a paper published in Nature Communications (4, article number: 2220) on 13 August 2013.

An international team of researchers worked on the project, initiated by associate professor Hui Ying Yang from Singapore University of Technology & Design and Rohit Karnik of the Department of Mechanical Engineering, Massachusetts Institute of Technology. The team included Dr Zhaojun Han and Prof Kostya (Ken) Ostrikov from CSIRO’s world-leading Plasma Nanoscience Laboratories.

Their paper reports that plasma-modified ultralong carbon nanotubes exhibit ultrahigh specific adsorption capacity for salt (exceeding 400% by weight) that is two orders of magnitude higher than that found in the current state-of-the-art activated carbon-based water treatment systems.

Prof Ostrikov attributes the success of the new membranes to the unique properties of plasma-treated carbon nanotubes: “Firstly, ultralong nanotubes have a very large surface area that is ideal for filtration. Secondly, nanotubes are easy to modify, which allows us to tailor their surface properties through localised nanoscale plasma treatment.”

Dr Han acknowledges that some smaller portable devices do already exist. However, because they rely on reverse osmosis and thermal processes, they are able to remove salt ions but are unable to filter out organic contaminants from the briny water found in some river and lake systems.

According to Dr Han, the project’s membranes could be integrated into portable water purification devices the size of a teapot that would be rechargeable, inexpensive and more effective than many existing filtration methods.

Now that the researchers have proved the effectiveness of the method, they plan to extend their research to other nanomaterials. They will begin by looking at graphene, which has similar properties to carbon nanotubes, but could be made considerably denser and stronger.