Science

Sunlight-activated powder disinfects water in just 60 seconds

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Among other potential applications, the powder could be used by backpackers collecting drinking water on the go
Depositphotos
A diagram of the purification process
Tong Wu/Stanford University
Among other potential applications, the powder could be used by backpackers collecting drinking water on the go
Depositphotos

If you leave a clear bottle of water in the sunlight, the ultraviolet rays will kill any harmful microbes in that water, making it drinkable … but it has to sit in the sun for at least six hours. A new sunlight-activated powder, however, does the job in a mere one minute.

Developed by scientists from Stanford University and the SLAC National Accelerator Laboratory, the powder is made up of nanoflakes of aluminum oxide, molybdenum sulfide, copper and iron oxide. All of these substances are readily available and inexpensive, plus only a small amount of the powder is required to treat a relatively large quantity of water.

Users start by stirring some of the powder into tainted water contained in a bottle or other transparent vessel, after which they leave it exposed to direct sunlight.

The molybdenum sulfide and copper absorb photons from the light, then act as a semiconductor/metal junction which allows the photons to release electrons. Those electrons are then free to react with the water, producing hydrogen peroxide and hydroxyl radicals which kill bacteria by rupturing their protective outer membranes.

Once the purification process is complete, any leftover hydrogen peroxide and hydroxyl radicals quickly break down into water and oxygen, leaving the water safe to drink. And because of their iron oxide content, the nanoflakes can be retrieved for reuse by swirling a magnet through the water.

A diagram of the purification process
Tong Wu/Stanford University

In a test of the technology, a small amount of the powder was added to a 200-ml (6.8-oz) beaker of room-temperature that was contaminated with approximately one million E. coli bacteria per milliliter. After the water had been left in natural sunlight for just 60 seconds, no live bacteria could be detected. What's more, the powder was able to be reused for 30 more treatments.

It is hoped that the technology could ultimately be utilized in impoverished regions which lack water purification infrastructure, or by people such as backpackers who collect water from streams and lakes. The powder might even find use at water treatment plants, which currently use artificial ultraviolet light to kill bacteria.

"During the day the plant can use visible sunlight, which would work much faster than UV and would probably save energy," said Stanford's Prof. Yi Cui, senior author of a paper on the research. "The nanoflakes are fairly easy to make and can be rapidly scaled up by the ton."

The paper was recently published in the journal Nature Water.

Source: Stanford University

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4 comments
Treon Verdery
Going with the idea that molybdenum disulphide is a planar molecule kind of like Graphene, just single digit micrograms might purify a liter of water, that would make a camping cup with a straw sprayed with this stuff that had 36 different interval of diffusion blobs, at 30 micrograms each, using up a microgram per liter per 24 hours make a water purifying, externally coated straw that lasted about 1100 uses, between when a child is 4 and 7 years old, with an entire amount of about just 1.2 milligrams of the photoctalytic nanothin flakes, if that is off an order of magnitude, the 11-14 milligrams are much less mass than a single iodine water purification tablet
Karmudjun
NIce article Ben - this is one that that I'll need to follow up on. I didn't see any mention of UV blocking polycarbonate being an issue - since the process of destroying bacteria revolves around the hydrogen peroxide, it appears UV doesn't factor into the effectiveness of this process. Still, I will need to drill down into this and see the effect upon viral contaminates before I get really enthusiastic. Just a quick read of your article, an excellent synopsis, I'll have to look into it all to answer my further concerns. Thanks for the continued information stream!
AlWe
Will it also deal with protozoans like Giardia?
Immortal Melvyn M. Lusterio
Excellent discovery, a potable crystal clean water can now be readily available anywhere but what I give is a free gift of the water of life! Alleluia! Amen! <3 O:) * (Y)