Controlling the Movement of Water Through Nanotube Membranes
Precise control of water transport through a nanotube
membrane is demonstrated by the new electro-chemical
approach. Photo Credit: Rensselaer
By fusing wet and dry nanotechnologies, Rensselaer
researchers have found a way to control the flow of water
through carbon nanotube membranes with an unprecedented level
of precision. The research will be described in the March 14,
2007 issue of the journal Nano Letters.
A group of researchers led by Nikhil Koratkar, associate
professor of mechanical engineering, has found a way to use
low-voltage electricity to manipulate the flow of water through
nanotubes. Control of water’s movement through a nanotube with
this level of precision has never been demonstrated
The researchers discovered that when the nanotube’s membrane
is given a small positive potential of only 1.7 volts, and the
water is given a negative potential, the nanotubes quickly
switch from repelling water to pumping water through the tube.
When the charge on the water is raised, the water flows through
at an exponentially faster rate. When the experiment is
reversed with a negatively charged nanotube, it takes much
higher voltage (90 volts) to move the water through the
By simply reversing the polarity of the nanotubes, the team
found that they could actually start and stop the flow of water
through the tube. When a small positive charge is administered
the water moves through the tube, and when that charge is
reversed the water flow stops.
The researchers determined that the nanotube walls had been
electrochemically oxidized as a result of water electrolysis,
meaning that oxygen atoms had coated the surface of the
nanotubes enabling the movement of water through the tube. Once
the charge is reversed, oxidation stops and the water can no
longer flow through the unoxidized portion of the tube.
The researchers also discovered that they could control the
rate of water flow through nanotubes sitting directly next to
each other, allowing one tube to pump quickly while the one
next to it didn’t pump water at all. Such an extreme difference
in water absorption so close together is unprecedented, and
could have major implications for time-released drug coatings,
lab-on-a-chip devices, and water capture.
With this enabling research in place, more efficient
micro-filtration and separation techniques can be created for
environmental restoration, the production of safe drinking
water, biomedical research, and advanced
Pulickel Ajayan, the Henry Burlage Professor of Materials
Science and Engineering at Rensselaer and a world-renowned
expert in fabricating nanotube materials, collaborated with
Koratkar on this project. Four other Rensselaer researchers
were involved with the research: Saroj Nayak, associate
professor of physics; post-doctoral researcher Lijie Ci; and
doctoral students Li Chen and Zuankai Wang.
The research was funded as part of a four-year $1.3 million
grant from the National Science Foundation.