Silver nanowire filters clean water

Silver nanowire filters clean water
Water filters comprising silver nanowires and carbon nanotubes could render water safe to drink by quickly and cheaply killing disease-causing bacteria. The filters also benefit from large pore size, which mean they do not get clogged nearly as quickly and do not need electric pumps to push water through them

Water filters comprising silver nanowires
This illustration from nano.govgives visual examples of the size and the scale of nanotechnology, showing us just how small nanotechnology actually is.and carbon nanotubes could render water safe to drink by quickly and cheaply killing disease-causing bacteria.
(A nanometer is one-billionth of a meter. In comparison, a human hair is about 100,000 nanometers in diameter).
The filters also benefit from large pore size, which mean they do not get clogged nearly as quickly and do not need electric pumps to push water through them.
The nanofilters were developed by researchers at Stanford University, US, using a cotton cloth as the base for the design. Silver nanowires were grown by reducing AgCl in poly(vinylpyridine) with ethylene glycol, followed by slow addition of silver nitrate. The mesh of silver nanowires was then laid over the cotton and then dipped in an ‘ink’ of carbon nanotubes, which coated the filter. An electric current was run through the filter and tests with water contaminated with high levels of E coli showed that it killed more than 98% of the bacteria. Without the electric field the killing power of the nanofilter is almost completely destroyed (Nano Letters, 2010, 10, 3628).
The researchers theorise that the filter is so effective at killing bacteria because the electric current substantially increases the levels of free silver ions. Silver has been shown to be an effective antibacterial agent, although the exact reason is still unclear, although it is likely to interfere with key enzymes and cell membrane viability.
Sudipta Seal, who has developed water nanofilters at the University of Central Florida, US, says that he would not include carbon nanotubes in any water filter he was building. He says that toxicity issues with the nanotubes would be too big a risk.
T Pradeep, a professor of nanoscience at the Indian Institute of Technology Madras, says the filter is interesting as it uses electricity to augment silver’s antibacterial action, but it is not ready for the real world yet. ‘This approach suffers from various disadvantages, such as use of electricity (applying 20V); battery discharge due to water electrolysis at such high voltages; use of carbon nanotubes; and inadequate antibacterial action.’
Walter, Patrick

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