New solar filter ensures clean drinking water by rapidly killing bacteria

An estimated 663 million people worldwide lack access to safe drinking water, yet finding an efficient way to disinfect the vital liquid has proved difficult.

However, researchers have designed a new device, which could solve this issue, using a resource readily available in most climates.

The disinfection device is powered by the sun, and can rapidly kill bacteria to deliver safe drinking water.

In their paper, published in Nature Nanotechnology, sunlight falling on the device killed more than 99.999 per cent of bacteria in just 20 minutes, leaving behind clean drinking water.

The device – which is around half the thickness of a postage stamp – has a striped surface made up of thin lines of molybdenum disulphide film, which the researchers call ‘nanoflakes’.

Molybdenum disulphide is usually used as an industrial lubricant, but its properties change depending on how many layers are in the material.

In this case, the film is only a few layers thick, which makes the material become a photocatalyst – a substance that speeds up reactions when exposed to light. Additionally, the researchers added a thin layer of copper to the film, which also acts as a catalyst to speed up reactions.The device consists of thin layers of molybdenum disulphide arranged like walls on a glass surface and topped with a thin layer of copper. Light falling on the walls triggers formation of hydrogen peroxide and other ‘reactive oxygen species’ that kill bacteria

The device consists of thin layers of molybdenum disulphide arranged like walls on a glass surface and topped with a thin layer of copper. Light falling on the walls triggers formation of hydrogen peroxide and other ‘reactive oxygen species’ that kill bacteria

This allowed the material to use sunlight to trigger specific reactions that produce ‘reactive oxygen species’ like hydrogen peroxide, which kill bacteria in the surrounding water.

Molybdenum disulfide is cheap and easy to make – an important consideration when making devices for widespread use in developing countries.

However the method is not a fix-all, as it only removes bacteria from water, and not other harmful chemicals.