Cleaning water with sunlight and nanotechnology

The filter, which is described in a paper in npj Clean Water, could become a useful purifier in places without access to reliable drinking water.

The secret ingredient is nanometre-sized wires made from titanium dioxide.

When combined with UV light, the nanowires cause small amounts of water (H2O) to react and become chemicals called Reactive Oxygen Species (ROS) - things like hydrogen peroxide (H2O2), hydroxide (OH-) and oxygen (O2-).

While not present in high enough amounts to be a problem for people, these compounds can all wipe out bacteria pretty efficiently.

The researchers, who are based at the Swiss Federal Institute of Technology Lausanne (EPFL), Switzerland, also found that when they combined the titanium dioxide nanowires with carbon nanotubes, the mixed material was even better at removing pathogens.

The researchers have shown that their filter can remove E. coli, and they say that this means it should be equally effective on other bacteria - and some large viruses.

Professor Lszl Forr, senior author on the paper, says that the filter's design was "a close collaboration between chemists, physicists and biologists".

"Our prototype can supply clean drinking water even at remote places to small populations and could be easily scaled-up," adds Forr.

"It is a great achievement. An important 'side-product' of this project is that it has attracted a large number of talented and motivated students who care for environmental issues, and for sustainability."

The researchers are now looking for ways to improve and fund their filter.

"I am convinced that it will create a strong follow-up in versatile scientific communities and hopefully funding agencies," says lead researcher Endre Horvth.