Researchers at Stanford University immersed a common cotton yarn in a mixture of silver nanowires and carbon nanotubes to make a new type of high-efficiency, inexpensive new water purification filter, which can kill 98% of bacteria in water and sterilize It is 80,000 times that of the traditional microporous mesh filter. The research results were published in the recently published "Nano Express" magazine.
Carbon nanotubes have good conductivity, and more than 98% of Escherichia coli can be killed if they stay in a 20-volt current for a few seconds. Silver can also be sterilized. Before pasteurization and refrigerators, people often put a silver coin on the bottom of a milk bottle to sterilize.
Sarah Halshone of the Stanford University Materials Research Bioengineering Experts Group said that filters made of carbon nanotubes and silver "hand in hand" can maximize the effectiveness of sterilization. The silver nanowires can kill any bacteria that are trapped in the pores, thus avoiding a major defect that is common in traditional filters, that is, bacteria will form a biofilm on the filter and foul the equipment.
Traditional filters use physical methods to adsorb bacteria, and the cotton fiber contained in the new filter is coated with a "nano-coat". The electric field formed by it can kill bacteria flowing through, and the cotton fiber has multiple layers and thick Up to 6.4 cm, enough to kill most bacteria in the water.
Cui Yi, associate professor of materials science and engineering at Stanford University, said that the cost of the new filter is also very low. On the one hand, silver nanowires use very little silver, and the cost is almost negligible. On the other hand, very little current is required. Nano-materials are highly adsorbable. The longer end of the silver nanowire is connected to the nanotube, and the other end extends into the gap between the cotton fibers. A smooth and gap-free coating will be formed on the cotton fiber. The conductive effect is very good. Therefore, the current intensity is only a few milliamperes, and a small solar cell or a pair of 12-volt car batteries can meet. The traditional filter uses an electric pump to pump water into the micropores, which consumes a large amount of power. In the laboratory, the same amount of water is filtered. The power consumption of the new filter is only 1/5 of the traditional filter.
Cui Yi also said that the purification speed of the new filter is very fast. The pores of the traditional filter are very small, and it is easy to block the pores when the bacteria are adsorbed and separated from the water. The pores of the new filter are relatively large, which only kills the bacteria but does not adsorb the bacteria. The water speed is 80,000 times that of traditional filters. This filter is practical in remote areas where chlorine gas cannot be used for water disinfection. It can greatly reduce the spread of cholera, typhoid and hepatitis and other diseases spread through water as a medium.
The researchers plan to develop filters that filter different types of bacteria in the next step, and test multiple combined filters.
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