Using nanoscale membranes to clean water on the moon

Anthony Straub is making major advances in water purification technology for industry and human consumption on Earth and in space, with his work on a nanotechnology membrane process taking a major step toward commercialization, thanks to a new NASA grant.

An assistant professor in the Department of Civil, Environmental and Architectural Engineering at the University of Colorado Boulder, Straub's research focuses on using membranes to improve water treatment.

"The membrane technology that is widely used now is essentially half a century old, and it has well-known limitations," Straub said. " It works well for many applications, but it has a tendency to let certain impurities through and it degrades if exposed to certain harsh chemicals."

NASA has awarded Straub and one of his PhD students, Kian Lopez,a phase one Small Business Innovation Research awardto develop a pilot water purification system for astronauts to use on a future Moon base.

Current space water purification systems are bulky and prone to repairs. The technology Straub's lab has developed only requires a pump to pressurize water, reducing size and weight. Low weight is especially important in moon missions, where every kilogram of cargo can cost tens of thousands of dollars.

"Current membranes remove impurities based on size and charge and, as a result, allow for small impurities to bypass the membrane," Straub said. "What we've designed traps a very small layer of air inside a membrane and the only way for the water to cross the barrier is by evaporating and then re-condensing on the other side, which impurities inherently cannot do."

The entire process occurs over a 100 nanometer span, a distance 160 times smaller than the width of a human hair, and the water that results is nearly pure H2O - distillation quality - since it has been turned to steam and then back to liquid.

These new membranes can be made from a wide variety of materials; the advance is in modifying them to create the air trapping layer. Although the work has been a longtime focus of Straub, he had not considered space applications or commercialization until Lopez returned from an internship at NASA.

"My mentor at NASA said this technology looks promising and the biggest impact we could have would be to start our own company," Lopez said.

Straub and Lopez decided to attend the New Venture Launch class together in the CU Boulder Leeds Business School, participating in campus technology transfer initiatives, including the New Venture Challenge and Lab Venture Challenge. They foundedOsmopure Technologies, Inc.in January of this year.

Space is but one application. Other potential is in municipal water systems and industry, particularly semiconductor or computer chip manufacturing, which requires ultrapure water.

Although ultrapure sounds like a marketing buzzword, it has aformal definition:water free of all minerals, particles, bacteria, microbes, and dissolved gasses. The needs go far beyond water that is safe for human consumption.

"The minimum for ultrapure water in chip manufacturing is a 14-step process right now. The final product must contain less than one 10-nanometer particle per milliliter of water, which would be the density equivalent of having only a single person on the entire planet Earth," Lopez said.

Semiconductor chips are manufactured in clean rooms, and ultrapure water is necessary to maintain temperature and humidity as well as to wash away residue produced during chip etching. Even the tiniest water impurities can damage the chips.

"Our work starts with NASA, but the beachhead market here on Earth is in ultrapure water production for semiconductors," Straub said. "This is a huge potential market, and we have filed a provisional patents with CU Venture Partners."

Straub is optimistic the grant will enable them to make significant progress in the coming months.

"This has been a four-year process, and at the beginning we didn't know if it would work," Straub said. "We started with theory and then went into the lab to test. The fabrication has gone through several iterations here in the CU labs. Now we are moving towards a commercial product, and the performance is impressive."

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