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Nanotechnology Membrane for High-Speed Water Sterilization

Published on 2010-09-16. Author : SpecialChem

Water purification is the removal of contaminants from untreated water to produce drinking water, sanitation. Substances that are removed during the process of drinking water treatment include suspended solids, bacteria, algae, viruses, fungi, minerals.

Courtesy of Yi Cui, Stanford University: Cotton fibers (big ones) surrounded by a special mixture of silver nanowires (small fibers).

Many research programs on water sterilization involve 'Nanotechnology'. More specifically nanoparticles of silver are very often cited for their antimicrobial properties. Recently a textile based device is has been developed that allows the high speed electrical sterilization of water, thanks to a research conducted by scientists of the Stanford University. The device consists of cotton fibers coated with a special mixture of silver nanowires and carbon nanotubes. They have unique ability to form complex multiscale coatings on cotton. This can produce an electrically conducting and high surface area device for the active, high-throughput inactivation of bacteria in water.

By using small amount of electricity the three-dimensional device can kill bacteria in water. The major raw material used is cotton as it is very cheap and easily available. The pores between fibers in cotton (tens to hundreds of micrometers) are much larger than the length scale of bacteria, which prevents the device from mechanically clogging during use.

Silver nanowires with diameters between 40 and 100 nm and up to 10 ┬Ám in length were used. They act as efficient electrical transport by reducing the number of electron hopping times.

Carbon nanotubes provide conformal conductive coatings to ensure good electrical conductivity over the entire active area of the device and used in solution as a porous electrode.

They tested the filtration device under different voltages, ranging from -20V up to +20V and by comparing silver nanowire/CNT cotton with CNT coated cotton only.

The silver nanowire/CNT cotton inactivates 89% of the bacteria at -20 V; at +20 V it inactivates 77%. However, neither filter effectively removes bacteria at zero potential.

Three stage serial application of this process may be used to effectively reach inactivation efficiencies of more than 98% of bacteria. According to the researchers further optimization of this device is still needed; but such innovation could be applied to water treatment in areas without access to chlorine treated water.

Source: SpecialChem Editorial Team

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