Friday, May 24, 2013

Nanoscavengers could usher in next generation water purification

Andrew Myers in Stanford Engineering News: Among its many talents, silver is an antibiotic. Titanium dioxide is known to glom on to certain heavy metals and pollutants. Other materials do the same for salt. In recent years, environmental engineers have sought to disinfect, depollute, and desalinate contaminated water using nanoscale particles of these active materials. Engineers call them nanoscavengers. The hitch from a technical standpoint is that it is nearly impossible to reclaim the nanoscavengers once in the water.

In a paper published online May 14 in the journal Nature Communications, an interdisciplinary team of engineers at Stanford University announces it has developed a new type of nanoscavenger with a synthetic core that is ultraresponsive to magnetism, allowing the easy and efficient recovery of virtually every one of the nanoscale purifiers.

“In contaminated water, nanoscavengers float around, randomly bumping into and killing bacteria or attaching themselves to the molecular pollutants they are after,” said Shan Wang, the study’s senior author and a professor of material science and engineering and jointly of electrical engineering. “When the contaminants are either stuck to the nanoscavenger or dead, the magnet is turned on and the particles vanish.”

...In their natural state, the new nanoscavengers are not magnetic and would not be attracted to another magnetic material. When the composite discs are exposed to a strong magnetic field, however, the magnetism of the two opposing fields turn into alignment, not just becoming magnetic but compounding the magnetic effect.

In doing so, the nanoscavengers become ultraresponsive to magnetism, far more so than the base iron oxide used in today’s technologies. The Stanford team has dubbed its advance with the oxymoronic name: “synthetic antiferromagnetic cores.” The prefix anti- in this case means in opposite direction, not non-magnetic....

The disc-like synthetic nanoscavengers collected magnetically. (Image: Mingliang Zhang, Stanford School of Engineering.)

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