Sunlight powered filter reliably eliminates pathogens

There are many areas on this planet where water is present, but also full of dangerous and harmful microbes. Inexpensive, reliable water filters can help ensure the drinking water supply of the population.

Reactive oxygen species filter water

Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have developed such an experimental water filter. It is a flat prototype, in which water is introduced through a hose at the top, which then flows through several layers of composite material sandwiched between two layers of glass, before being discharged again through a hose at the bottom.

The composite material consists of titanium dioxide nanowires interwoven with carbon nanotubes. When the filter is exposed to sunlight, the ultraviolet spectrum of light activates the composite to produce a group of molecules called reactive oxygen species. These molecules include hydrogen peroxide and oxygen.

Two liters of water a day to start with

The molecules from the group of reactive oxygen species kill dangerous bacteria and viruses very effectively. The filter developed by EPFL has already been successfully tested on water contaminated with E. coli bacteria. However, it should also have no problems with other pathogens. The researchers assume that the method can also be used to remove micro-pollutants such as pesticides or medicine residues.

Both titanium dioxide nanowires activated with sunlight and UV light alone are capable of killing microbes. However, according to Professor László Forró, head of the EPFL team, the newly developed filter is much more effective. This is partly due to the carbon nanotubes’ ability to absorb heat from sunlight, speeding up the process. The small prototype can filter 2 liters of water per day. As technology advances, that amount would increase dramatically. The efficiency of the filter can be further increased by adding a small amount of gold nanoparticles to the composite material.

In close collaboration between chemists, physicists and biologists, we have developed a highly efficient water purification device that does not require any energy source but sunlight. Our prototype can provide clean drinking water even in remote places“says Forro.