Navigation Links
High-speed filter uses electrified nanostructures to purify water at low cost
Date:8/31/2010

By dipping plain cotton cloth in a high-tech broth full of silver nanowires and carbon nanotubes, Stanford researchers have developed a new high-speed, low-cost filter that could easily be implemented to purify water in the developing world.

Instead of physically trapping bacteria as most existing filters do, the new filter lets them flow on through with the water. But by the time the pathogens have passed through, they have also passed on, because the device kills them with an electrical field that runs through the highly conductive "nano-coated" cotton.

In lab tests, over 98 percent of Escherichia coli bacteria that were exposed to 20 volts of electricity in the filter for several seconds were killed. Multiple layers of fabric were used to make the filter 2.5 inches thick.

"This really provides a new water treatment method to kill pathogens," said Yi Cui, an associate professor of materials science and engineering. "It can easily be used in remote areas where people don't have access to chemical treatments such as chlorine."

Cholera, typhoid and hepatitis are among the waterborne diseases that are a continuing problem in the developing world. Cui said the new filter could be used in water purification systems from cities to small villages.

Faster filtering by letting bacteria through

Filters that physically trap bacteria must have pore spaces small enough to keep the pathogens from slipping through, but that restricts the filters' flow rate.

Since the new filter doesn't trap bacteria, it can have much larger pores, allowing water to speed through at a more rapid rate.

"Our filter is about 80,000 times faster than filters that trap bacteria," Cui said. He is the senior author of a paper describing the research that will be published in an upcoming issue of Nano Letters. The paper is available online now.

The larger pore spaces in Cui's filter also keep it from getting clogged, which is a problem with filters that physically pull bacteria out of the water.

Cui's research group teamed with that of Sarah Heilshorn, an assistant professor of materials science and engineering, whose group brought its bioengineering expertise to bear on designing the filters.

Silver has long been known to have chemical properties that kill bacteria. "In the days before pasteurization and refrigeration, people would sometimes drop silver dollars into milk bottles to combat bacteria, or even swallow it," Heilshorn said.

Cui's group knew from previous projects that carbon nanotubes were good electrical conductors, so the researchers reasoned the two materials in concert would be effective against bacteria. "This approach really takes silver out of the folk remedy realm and into a high-tech setting, where it is much more effective," Heilshorn said.

Using the commonplace keeps costs down

But the scientists also wanted to design the filters to be as inexpensive as possible. The amount of silver used for the nanowires was so small the cost was negligible, Cui said. Still, they needed a foundation material that was "cheap, widely available and chemically and mechanically robust." So they went with ordinary woven cotton fabric.

"We got it at Wal-mart," Cui said.

To turn their discount store cotton into a filter, they dipped it into a solution of carbon nanotubes, let it dry, then dipped it into the silver nanowire solution. They also tried mixing both nanomaterials together and doing a single dunk, which also worked. They let the cotton soak for at least a few minutes, sometimes up to 20, but that was all it took.

The big advantage of the nanomaterials is that their small size makes it easier for them to stick to the cotton, Cui said. The nanowires range from 40 to 100 billionths of a meter in diameter and up to 10 millionths of a meter in length. The nanotubes were only a few millionths of a meter long and as narrow as a single billionth of a meter. Because the nanomaterials stick so well, the nanotubes create a smooth, continuous surface on the cotton fibers. The longer nanowires generally have one end attached with the nanotubes and the other end branching off, poking into the void space between cotton fibers.

"With a continuous structure along the length, you can move the electrons very efficiently and really make the filter very conducting," he said. "That means the filter requires less voltage."

Minimal electricity required

The electrical current that helps do the killing is only a few milliamperes strong barely enough to cause a tingling sensation in a person and easily supplied by a small solar panel or a couple 12-volt car batteries. The electrical current can also be generated from a stationary bicycle or by a hand-cranked device.

The low electricity requirement of the new filter is another advantage over those that physically filter bacteria, which use electric pumps to force water through their tiny pores. Those pumps take a lot of electricity to operate, Cui said.

In some of the lab tests of the nano-filter, the electricity needed to run current through the filter was only a fifth of what a filtration pump would have needed to filter a comparable amount of water.

The pores in the nano-filter are large enough that no pumping is needed the force of gravity is enough to send the water speeding through.

Although the new filter is designed to let bacteria pass through, an added advantage of using the silver nanowire is that if any bacteria were to linger, the silver would likely kill it. This avoids biofouling, in which bacteria form a film on a filter. Biofouling is a common problem in filters that use small pores to filter out bacteria.

Cui said the electricity passing through the conducting filter may also be altering the pH of the water near the filter surface, which could add to its lethality toward the bacteria.

Cui said the next steps in the research are to try the filter on different types of bacteria and to run tests using several successive filters.

"With one filter, we can kill 98 percent of the bacteria," Cui said. "For drinking water, you don't want any live bacteria in the water, so we will have to use multiple filter stages."

Cui's research group has gained attention recently for using nanomaterials to build batteries from paper and cloth.


'/>"/>

Contact: Louis Bergeron
louisb3@stanford.edu
650-725-1944
Stanford University
Source:Eurekalert  

Related biology technology :

1. Supelco(R) Expands Ascentis(R) Express HPLC Columns Line for High-Speed and High-Efficiency Separations
2. Frost & Sullivan Recognizes Kraton Polymers for Developing a New Generation of Polymer Grades Suitable for High-Speed Processing in Nonwoven Manufacture
3. Signatec Unveils PX14400, Its High-Speed PCI-Express Digitizer Capable of Sustained Recordings Over 1.2 GB/s with Xilinx Virtex-5 FPGAs for Embedded Real-Time Processing
4. Smallest nanoantennas for high-speed data networks
5. IGEN Networks signs Exclusive Agreement with Machlink, for wireless technology with high-speed Internet, phone and data applications
6. Filter Markets - Discover the Growth Segments
7. New Gas Clean Filter Technology From Varian, Inc. Reduces Contamination in GC, ICP and GC/MS
8. Regal Introduces Four, Six and Eight Port Filtered and Un-Filtered Right Angle BNC Connectors
9. ElutraSep Inc. Announces the Launch of the Cryptonite™ HV Filter Module for Cryptosporidium and Giardia Testing
10. Angiotech Pharmaceuticals announces FDA 510(k) clearance of the Option(TM) Inferior Vena Cava Filter
11. Oclaro(TM) Hits Milestone With Clarity(TM) Fluorescence Filters
Post Your Comments:
*Name:
*Comment:
*Email:
Related Image:
High-speed filter uses electrified nanostructures to purify water at low cost
(Date:4/25/2017)... , ... April 25, 2017 , ... ... Physical Medicine & Rehabilitation, P.A. , proudly announced today that acclaimed physiatrist Matthew ... his duties on May 15, 2017. , Dr. Terzella completed his residency in ...
(Date:4/25/2017)... SEATTLE, WA (PRWEB) , ... April 25, 2017 , ... ... technology division of Quorum, will be featured in multiple sessions at this week’s ... range from emerging trends to best practices in clinical research. , "We are excited ...
(Date:4/24/2017)... YORK , April 24, 2017  Dante Labs announced ... at only EUR 850 (ca. $900). While American individuals have ... the first time Europeans can access WGS below EUR 1,000. ... are crucial to leveraging genetic information to make informed decisions ... ...
(Date:4/21/2017)... ... April 21, 2017 , ... Having worked on the ... Formaspace is pleased to introduce it to top lab design architects from around the ... Turk and VP of Industrial Design and Engineering Greg Casey will be at the ...
Breaking Biology Technology:
(Date:3/29/2017)... the health IT company that operates the largest health ... today announced a Series B investment from BlueCross BlueShield ... investment and acquisition accelerates higi,s strategy to create the ... activities through the collection and workflow integration of ambient ... secures data today on behalf of over 36 million ...
(Date:3/24/2017)... -- The Controller General of Immigration from Maldives Mr. ... have received the prestigious international IAIR Award for the most innovative high ... ... Maldives Immigration Controller ... (small picture on the right) have received the IAIR award for the ...
(Date:3/23/2017)... Mar. 23, 2017 Research and Markets has ... Analysis & Trends - Industry Forecast to 2025" report to ... ... a CAGR of around 8.8% over the next decade to reach ... analyzes the market estimates and forecasts for all the given segments ...
Breaking Biology News(10 mins):