Cotton Water Filters

A recent article at the New Scientist reports on some nanotechnology research that might provide a new, inexpensive method of purifying water in remote areas.  A team at Stanford University, led by Li Cui, developed the filtering material by adding carbon nanotubes and silver nanowires to ordinary cotton fabric.

The fabric is easy to produce, says lead researcher Yi Cui at Stanford University in California. Cui’s team simply dip a piece of cotton into a solution of CNTs and then pipette droplets containing silver nanowires onto the cotton.

The carbon adheres to individual fibers in the cotton, and the silver then forms a grid between them.  This allows the fabric to conduct electricity.  Only a weak electric current is used; but, in combination with the anti-bacterial properties of the silver, it is apparently enough to kill many bacteria.  In a test reported [abstract] in Nano Letters, published by the ACS, the researchers found that a single pass through the filter material removed 89% of E. coli bacteria; three passes removed more than 98%.   They calculate a gravity-fed device could filter 100,000 liters/hour per square meter of filter area.  Because it does not require mechanical pumps, the filter uses only about 20% of the energy of conventional filters.

This is preliminary research; the team still needs to test the material with other microorganisms, and needs to make sure that the filter does not shed material, particularly the carbon nanotubes, into the filtered water.  Still, this is potentially a very promising development.  For a sizable chunk of the world’s population, getting clean water is a serious challenge.  Anything that could make it easier and more economically feasible would be a significant step forward.

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