Environmental Protection

Scientists Combine Silver and Electricity to Kill Bacteria in Water

A report on a new, inexpensive filtering technology that kills up to 98 percent of disease-causing bacteria in water appears in the latest issue of Nano Letters, a monthly American Chemical Society journal.

Yi Cui, Ph.D., of Stanford University in Stanford, Calif., and colleagues explain in “High Speed Water Sterilization Using One-Dimensional Nanostructures” that most water purifiers work by trapping bacteria in tiny pores of filter material. Pushing water through those filters requires electric pumps and consumes a lot of energy. In addition, the filters can get clogged and must be changed periodically. The new material, in contrast, has relatively huge pores, which allow water to flow through easily. And it kills bacteria outright, rather than just trapping them.

The scientists knew that contact with silver and electricity can destroy bacteria and decided to combine both approaches. They spread sub-microscopic silver nanowires onto cotton and then added a coating of carbon nanotubes, which give the filter extra electrical conductivity.

Tests of the material on E. coli-tainted water showed that the silver/electrified cotton killed up to 98 percent of the bacteria. The filter material never clogged, and the water flowed through it very quickly without any need for a pump.

“Such technology could dramatically lower the cost of a wide array of filtration technologies for water as well as food, air, and pharmaceuticals where the need to frequently replace filters is a large cost and difficult challenge,” their report states.

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