A new sunscreen to effectively decontaminate water

Access to clean and safe drinking water is essential to life. However, water pollution due to environmental conditions and poor waste management in some parts of the world is a serious problem for access to clean and safe drinking water. This problem is particularly critical in regions with little electricity, where advanced water purification methods do not exist. Unsafe water supplies are linked to the transmission of diseases such as cholera, diarrhoea, dysentery and typhoid fever.

Now, a team of scientists led by EPFL’s László Forró has developed a new water purification filter that combines titanium dioxide (TiO2) nanowires and carbon nanotubes powered only by light from the sunlight to decontaminate water safely and effectively.

Only TiO2 nanowires can effectively purify water in the presence of sunlight.

But intertwining the nanowires with the carbon nanotubes forms a composite material that adds an extra layer of decontamination by pasteurizing the water, killing human pathogens like bacteria and large viruses.

Contaminated water enters through a tube at the top, passes through a multi-layer filter material sandwiched between two sheets of glass, and exits through a tube at the bottom. When ultraviolet light from the visible spectrum of sunlight hits the filter, it causes the compound to produce a group of molecules called reactive oxygen species. These include hydrogen peroxide, hydroxide, and oxygen, and are known to be effective pathogen killers.

The filter has already been successfully tested on water containing E. Coli bacteria, the “gold standard” for bacterial survival studies.

The results indicate that it should also have no problem eradicating other pathogens. The water filter is exceptionally adept at removing all pathogens from water and shows promising results even in removing micro-pollutants, such as pesticides, drug residues, cosmetics, etc.

In close collaboration between chemists, physicists and biologists, we have developed a very efficient water purification device, which does not need any energy source but sunlight. Our prototype can supply small towns with drinking water even in remote locations and could be easily extended. It’s been a great achievement, and an important ‘by-product’ of this project is that it has attracted a large number of talented and motivated students who care about environmental issues, about sustainability.

Laszlo Forro

More information: www.nature.com (English text).

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