About 663 million people in this world has little access to safe
drinking water, facing effective way to disinfect the drinking water for their
consumption. To address this problem, many researches have been done to develop
such a device which can disinfect the contaminated water by using natural
energy that is available in most climate. The disinfection device is powered by the sun, and can rapidly kill
bacteria to deliver safe drinking water.
Department of Energy's SLAC National Accelerator Laboratory and Stanford University in California has designed such solar energy device can disinfect water in a more efficient way. While other solar energy water purification system relies on ultraviolet light, which represents only four per cent of the total solar energy. This leads to a very slow treatment speed of up to 48 hours, limiting the amount of water people can disinfect.
To overcome this issue, the
researchers developed new materials that can harvest visible light – which
represents around 50% of solar energy - and speed up solar water purification.
An extremely thin films of
molybdenum disulphide – an inorganic compound consist of molybdenum and sulphur
are used this device development. Dr Chong Liu, lead author of the study, said:
“Our device looks like a little rectangle of black glass. We just dropped it
into the water and put everything under the sun, and the sun did all the work.”
This information is 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.
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.
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