119 innovations

Nanoscavengers for water purification

WHO and UNICEF have set a 2030 target for everyone to have access to a safe drinking-water supply and new water-purifying “nanoscavengers” developed by researchers at Stanford University could help achieve this goal. There are various nanoparticles that boast different water-purifying properties. Silver nanoparticles act as an antibiotic, titanium dioxide nanoparticles trap heavy metals and pollutants, while others capture salt. Engineers call these kinds of particles nanoscavengers.

The main problem has been reclaiming the nanoscavengers from the water once they have performed their clean up duties. Some approaches that are already in use commercially involve giving the nanoscavengers a core of iron oxide to make them magnetic, meaning they can then be removed using magnets. The downside of this method is that it isn’t possible to remove all the nanoscavengers because iron oxide isn’t absolutely responsive to magnetism.

To overcome this problem, the Stanford team developed a new type of nanoscavenger that sees the iron oxide core replaced with a synthetic core. This new core is a disk made up of magnetic outer layers sandwiched either side of a titanium center. This composition makes the new nanoscavengers non-magnetic in their natural state, so they aren’t attracted to each other or other magnetic materials.

However, when the synthetic core is exposed to a strong magnetic field, the magnetism of the two opposing fields align so they not only become magnetic, but the magnetic effect is compounded to make them ultraresponsive to magnetism.

In a side-by-side test against the aforementioned iron oxide core nanoscavengers, the synthetic core nanoscavengers killed 99.9 percent of the E. coli bacteria in 20 minutes and allowed virtually all of the nanoscavengers to be removed from the water after a five minute exposure to a permanent magnet.