December 2, 2023

If you put a bottle of clean water in the sun, the UV light will kill any harmful microbes in the water, making it drinkable…but it has to be in the sun for a while At least six hours. However, a new sun-activated powder does the job in just a minute.

The powder, developed by scientists at Stanford University and SLAC National Accelerator Laboratory, consists of nanoflakes of alumina, molybdenum sulfide, copper and iron oxide. All of these substances are readily available and inexpensive, and only small amounts of powder are required to treat relatively large amounts of water.

Users first stir some of the powder into contaminated water in a bottle or other clear container, which is then exposed to direct sunlight.

Molybdenum sulfide and copper absorb photons from light and then act as a semiconductor/metal junction, allowing the photons to release electrons. These electrons are then free to react with water, producing hydrogen peroxide and hydroxyl radicals, which kill bacteria by damaging their protective outer membrane.

After the purification process is complete, any remaining hydrogen peroxide and hydroxyl radicals are quickly broken down into water and oxygen, making the water safe to drink. Because they contain iron oxide, the nanoflakes can be recycled and reused by spinning a magnet in water.

Schematic diagram of the purification process
Schematic diagram of the purification process

Tong Wu/Stanford University

In a test of this technique, a small amount of powder was added to a 200 ml (6.8 oz) room temperature beaker, which was filled with approximately 1 million Escherichia coli The number of bacteria per milliliter. After exposing the water to natural sunlight for just 60 seconds, no live bacteria could be detected. What’s more, this powder can be reused for more than 30 treatments.

The hope is that the technology could eventually be used in impoverished areas that lack water purification infrastructure, or by people such as backpackers who collect water from streams and lakes.This powder may even be used in the present Artificial Ultraviolet light kills bacteria.

“During the day, the plant can use visible light, which acts much faster than ultraviolet light and potentially saves energy,” said senior author Professor Yi Cui of Stanford University. “The nanoflakes are fairly easy to make and can be scaled up to the ton very quickly.”

The paper was recently published in the journal Natural water.

source: Stanford University