drinking water – Scientists Talk Funny

More than a billion people drink water that is contaminated and can spread deadly diseases such as cholera, dysentery, hepatitis A, typhoid, polio and diarrhea.

Most contaminated water could be purified by adding hydrogen peroxide, which safely kills many of the disease-causing organisms and oxidizes organic pollutants to make them less harmful. Hydrogen peroxide disinfects water in a similar way as standard water chlorination, but it leaves no harmful residual chemicals. Unfortunately, it’s difficult to make or obtain hydrogen peroxide in rural settings with limited energy sources.

Now, researchers from Stanford University and SLAC National Accelerator Laboratory have developed a portable device that produces hydrogen peroxide from oxygen gas and water — and it can be powered by a battery or conventional solar panels. You can hold the small device in one hand.

“The idea is to develop an electrochemical cell that generates hydrogen peroxide from oxygen and water on site, and then use that hydrogen peroxide in ground water to oxidize organic contaminants that are harmful for humans to ingest,” said Christopher Hahn, PhD, a SLAC associate staff scientist, in a recent news release.

First, the researchers designed and synthesized a catalyst that selectively speeds up the chemical reaction of converting oxygen gas into hydrogen peroxide. For this application, standard platinum-mercury or gold-plated catalysts were too expensive, so they investigated cheaper carbon-based materials.

Next, they used their carbon-based material to build a low-cost, simple and robust device that generates and stores hydrogen peroxide at the concentration needed for water purification, which is one-tenth the concentration of the hydrogen peroxide you buy at the drug store for cleaning a cut. Although this device uses materials not available in rural communities, it could be cheaply manufactured and shipped there.

Their results were recently reported in Reaction Chemistry and Engineering. However, more work needs to be done before a higher-capacity device will be available for use.

“Currently it’s just a prototype, but I personally think it will shine in the area of decentralized water purification for the developing world,” said Bill Chen, first author and a chemistry graduate student at Stanford. “It’s like a magic box. I hope it can become a reality.”

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine. For more details, please read my SLAC news release.

Photograph, of researcher Chong Liu holding their nanostructured device, by Jin Xie.

Millions of people in developing countries lack access to safe drinking water, a primary cause of disease. Now, researchers from Stanford University and SLAC National Accelerator Laboratory have developed a tiny gadget that may help address this huge global health issue.

Their device — the size of half a postage stamp — uses solar energy to more efficiently purify water.

Solar energy is already commonly used to disinfect drinking water, particularly in areas with limited fuel to boil water. However, solar disinfection mostly relies on killing pathogens in the water with ultraviolet light, which represents only 4 percent of the sun’s total energy. This slow and inefficient purification process takes six to 48 hours.

The Stanford research team devised a new material that can significantly speed up this process by harvesting the whole spectrum of visible light, which corresponds to over 50 percent of solar energy. As reported this week in Nature Nanotechnology, they were able to disinfect nearly all of the bacteria in a small water sample in just 20 minutes.

“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,” said Chong Liu, PhD, lead author and postdoctoral researcher in materials science and engineering at Stanford, in a recent news release, which describes the device:

Under an electron microscope the surface of the device looks like a fingerprint, with many closely spaced lines. Those lines are very thin films — the researchers call them “nanoflakes” — of molybdenum disulfide that stacked on edge, like the walls of a labyrinth, atop a rectangle of glass.

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By making their molybdenum disulfide walls in just the right thickness, the scientists got them to absorb the full range of visible sunlight. And by topping each tiny wall with a thin layer of copper, which also acts as a catalyst, they were able to use that sunlight to trigger exactly the reactions they wanted — reactions that produce “reactive oxygen species” like hydrogen peroxide, a commonly used disinfectant, which kill bacteria in the surrounding water.

Although promising, the researchers’ method doesn’t remove chemical pollutants and it has only been tested on three strains of bacteria mixed with less than an ounce of water in the lab. The next step will be to test the device in a real-world stew of contaminants.

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.