Nano Express: Nano Water Filter Kills 98% of Bacteria in Water

According to a recent report by the American Physicists Organization Network, researchers at Stanford University immersed a common cotton yarn in a mixture of silver nanowires and carbon nanotubes to create an efficient, inexpensive new type of water purification filter. Kill 98% of the bacteria in the water, sterilization speed is 80,000 times the traditional microporous mesh filter. The research results were published in the recently published Nano Express newspaper.

Carbon nanotubes have good conductivity, and more than 98% of E. coli will be killed if it stays on the 20-volt current for a few seconds. Silver can also be sterilized. Prior to pasteurization and the appearance of refrigerators, people often placed a silver coin at the bottom of the milk bottle to disinfect.

Sarah Haiershaw of Stanford University's Materials Research and Bioengineering Experts Group said that carbon nanotubes and silver, both of which are made of materials that work together, maximize the bactericidal efficacy. The silver nanowires can kill any bacteria trapped in the pores, thus avoiding the common deficiencies of conventional filters, ie, bacteria can form biofilm on the filter and thus deface the device.

Traditional filters use physical methods to adsorb bacteria. The cotton fibers contained in the new filter are coated with a “nano coat,” which forms an electric field that kills bacteria that flow through, and cotton fibers have multiple layers that are thick. Up to 6.4 cm, enough to kill most bacteria in the water.

According to Cui Yi, an associate professor of materials science and engineering at Stanford University, the cost of this new filter is also very low. On the one hand, the silver used for silver nanowires is very small and the cost is almost negligible. On the other hand, the required current is very small. The adsorption of nanomaterials is very high. The longer end of the silver nanowires is connected to the nanotubes, and the other end extends into the gaps in the middle of the cotton fibers. A smooth, gap-free coating is formed on the cotton fibers. The conductive effect is very good. Therefore, the current intensity is only a few milliamps, and a small solar cell or a pair of 12-volt car batteries can satisfy. The traditional filter uses an electric pump to pump water into the micro-holes, which consumes a large amount of electricity and filters the same amount of water in the laboratory. The new filter consumes only one-fifth the power of traditional filters.

Cui Yi also said that the purification speed of the new filter is very fast. The filter pores of traditional filters are very small, and it is very easy to block micropores when bacteria are adsorbed and separated from water. The new filter has large pores that only kill bacteria but does not adsorb bacteria. Therefore, it does not slow down the flow of water. Water speed is 80,000 times that of conventional filters. This type of filter is practical in remote areas where chlorine cannot be used to disinfect water, and it can greatly reduce the spread of diseases such as cholera, typhoid, and hepatitis that are transmitted through water as a medium.

The researchers plan to next develop filters that filter against different types of bacteria and test multiple combinations of filters.