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March 13th, 2012

CNT ‘nanobrushes’ coated with nanocatalysts show promise for cleaning polluted water

Published on March 13th, 2012 | Edited by: Eileen De Guire

A Pakastani mother gives her child clean water in Charsarda District, an area severely affected by monsoon floods. The UN World Water Assessment Programme released its triennial report on global water issues. Credit: UNICEF/ZAK; UN.

The theme of this year’s United Nations World Water Day (March 22) is “Water and Food Security.” Every three years the UN World Water Assessment Program releases a report that provides an “authoritative picture of the state, use and management of the world’s freshwater resources.” The 4th edition of the United Nations World Water Development Report was released yesterday in conjunction with the first day of the 6th World Water Forum being held this week in Marseille, France.

The report is big — three volumes totaling over 2,000 pages: Vol. 1, Managing Water under Uncertainty and Risk; Vol. 2, Knowledge Base and Vol. 3, Facing the Challenges. The press release accompanying the report begins, “Surface and groundwater resources in Europe and North America often contain a mix of pollutants, such as nutrients, metals, pesticides, microbes, industrial chemicals and pharmaceutical products, all of which have adverse effects on freshwater ecosystems and human health, warns the United Nations.”

A powerful new tool could soon be added to the water purification arsenal. A professor at Wright State University, Sharmila Mukhopadhyay, is making coated carbon nanotube devices, and they appear to be able to meet the challenge to remove a variety of pollutants from freshwater.

Electron microscope image of nanocatalyst particles on carbon nanotubes. Credit: Mukhopadhyay; Wright State University

The device is comprised of CNTs grown on porous substrates and coated with active nanoparticles. It is like a fuzzy nanobrush with extremely high surface area and can be customized to the clean-up job. She says in an email, “Nanocatalysts can be attached to these surfaces for breaking up pollutants or facilitating other reactions.” For example, silver is an anti-bacterial agent, palladium catalyzes the decomposition of carbon-tetrachloride and titania is a sun-activated photocatalyst.

In regard to the material’s multifunctionality, Mukhopadhyay says in a university press release, “simultaneously you can combine multiple environmental cleanup applications into one single component. In an Innovation News Daily story online, she said, “These are very, very small samples able to clean quite a bit of water.” In her lab, researchers have made CNT purifiers 2 millimeters by 4 millimeters that can purify a few gallons at a time.

The “nanobrush” purifiers build on earlier work published in 2009, where her team demonstrated the ability to grow CNTs on porous substrates, mimicking the “hierarchical branching” common in biological systems with internal and external functional surfaces thanks to “coatings” of capillaries, hairs, alveoli, etc., Up to then, most CNTs were grown on flat, nonporous surfaces.

Growing the CNTs on porous platforms imparts benefit, too. Mukhopadhyay explained, “They provide the advantages of nano-structures without the environmental concerns, since the nanomaterials are strongly attached to larger robust substrates and do not escape into the environment.”

Mukhopadhyay and several industrial partners, including MetaMateria Technologies of Columbus, Ohio, recently won Ohio Third Frontier funding of just under $1 million for a project to commercialize the technology. The successful proposal was titled, “Water Purification using Nano-Enabled Solutions.”

Mukhopadhyay, a past president of ACerS’ Electronics Division, is director of Wright State’s Center for Nano-Scale Multifunctional Materials and professor of mechanical and materials engineering.


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