International research team develops portable device that produces hydrogen peroxide for purifying drinking water

Some two billion people in the world lack access to clean drinking water. University of Calgary researcher Dr. Samira Siahrostami, PhD, is determined to help them.

“I’m really passionate about this issue. We have to do something,” says Siahrostami, assistant professor of physical and theoretical chemistry in the Faculty of Science’s Department of Chemistry.

Now, as part of an international research team, Siahrostami has taken a big step toward providing people in remote and rural locations, such as in developing countries, with clean and safe water.

The team has developed a portable device that uses a cost-effective, efficient carbon-based catalyst material to produce hydrogen peroxide. The hydrogen peroxide can then be used to purify local water sources contaminated by bacteria and other micro-organisms and inorganic pollutants from urban, industrial and agricultural waste.

The compact device, essentially an electrochemical cell, needs only oxygen and water and can be powered by small conventional solar panels.

“We expect this technology to be useful for water treatment in remote locations where sources of water are contaminated and there’s no access to public water-purification systems,” Siahrostami says.

In addition to UCalgary, the research team included scientists from Harvard University, Rice University, Stanford University, Northeastern University (Burlington, Massachusetts), Brookhaven National Laboratory (New York), and Canadian Light Source Inc. at the University of Saskatchewan.

The team’s study, “Highly Selective Oxygen Reduction to Hydrogen Peroxide on Transition Metal Single Atom Co-ordination,” is published in Nature Communications, a journal in the top-ranked Nature series.

Iron catalyst used to produce hydrogen peroxide

Large-scale water treatment plants — including those in Calgary — use chlorine to purify ‘raw’ water sources. However, hydrogen peroxide is just as effective at treating water as chlorine, which can affect smell and taste and produce byproducts, some of them carcinogenic at high concentrations.

“The only byproducts of using hydrogen peroxide to treat water are water and oxygen,” Siahrostami notes.

Yet only about one per cent of the world’s water treatment plants use hydrogen peroxide, because it is more expensive than chlorine to produce at industrial scale and transport to cities and towns, she says.

That prompted Harvard University scientists to investigate carbon-based catalyst materials capable of lowering the cost and increasing the efficiency of hydrogen peroxide production. They found that an iron “single atom catalyst” — single iron atoms dispersed and embedded in a carbon nanotube — had the best performance in producing hydrogen peroxide.

Oxygen gas flows through the carbon nanotube and interfaces with the catalyst (which speeds up the electrochemical reaction), which reduces the oxygen to hydrogen peroxide.

Siahrostami led the study’s theoretical work, doing much of it at Stanford University prior to joining UCalgary about a year ago. Her team used quantum mechanical computational models to understand the origin of the catalytic activity, and the co-ordination network of iron, oxygen and carbon atoms in the carbon nanotube that produced the most hydrogen peroxide.

The team collaborated with the Canadian Light Source facility, which used X-ray absorption spectroscopy to determine the structure of the catalyst’s surface and its atomic-scale co-ordination network.

“We were able to see at the atomic scale what is happening in the device on the iron catalyst’s surface,” Siahrostami says. “This enabled us to tune, or direct, the reaction toward the production of hydrogen peroxide. That is the key discovery.”

Device efficiently kills contaminants

Siahrostami’s main collaborator, Dr. Haotian Wang, PhD (now an assistant professor of chemical and biomolecular engineering at Rice University), built a laboratory-scale device and tested the hydrogen peroxide it produced on E. coli bacteria, a common water contaminant.

Only a few milligrams of hydrogen peroxide are needed to treat one litre of water, Siahrostami notes. “If you operate the device for two hours, it completely removes the E. coli in contaminated water. So it works very efficiently.”

The device works in ambient conditions, without high pressures or high temperatures. Siahrostami says that a breakthrough, compared with other carbon-based catalysts she has previously investigated, is that the iron single atom catalyst works in neutral pH conditions and over a wider pH range than chlorine. This means the hydrogen peroxide produced by the device can be mixed directly with water of diverse quality.

Siahrostami and her research group’s next step is to explore using a less expensive material than the carbon nanotube, such as carbon black, which would significantly lower the device’s cost.

“The technology is already very efficient and ready to go,” Siahrostami says. “We just need to scale it up and make it affordable for everyone in the developing world.”

UCalgary’s Canada First Research Excellence Fund program, the Global Research Initiative in Sustainable Low Carbon Unconventional Resources, supported Siahrostami’s research.