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Researchers testing new coating to counter nitrogen oxides

By Damir Beciri
23 December 2012

coating-breaksdown-nitrogen-oxidesIn our previous articles, we often mentioned air quality since it affects our health and quality of life. Despite the fact you might pay attention to the materials, finishes and proper ventilation inside your home, people living in urban areas still suffer from high levels of pollution from automotive traffic. Fraunhofer Institute researchers plan to develop and investigate how coated panels could counter this problem.

Aside carbon-dioxide (CO2), current automotive traffic is the major source of nitrogen oxides (NOx). Nitrogen oxides are a group of gaseous compounds, all of which contain nitrogen and oxygen in varying amounts – the most common two are nitric oxide (NO) and nitrogen dioxide (NO2). Exposure to NOx has been shown to cause varying levels of symptoms, depending on the level of exposure. NO2 exposure concentrations near roadways are of particular concern for susceptible individuals such as people with asthma asthmatics, children, and the elderly.

While motor industry should strive to stricter standards which lower the pollution, a group of researchers led by Dr. Michael Hüben of the Fraunhofer Institute for Molecular Biology and Applied Ecology (Fraunhofer IME) in Schmallenberg, Germany, are conducting a program named “Effectiveness of photo-catalytic removal of nitrogen oxide on coated building test panels” – a program with a goal to test how photo-catalytic surfaces could contribute to the removal of NOx, as well as their durability and efficiency over long-term operation.

”Coatings that are photo-catalytically active can help to reduce nitrogen oxides“, claims Hüben, “There are already a number of products available for the photo-catalytic coating of surfaces, but the measurement method standardized according to ISO 22197-1 cannot be applied to all problems. At the IME, we have now developed a special measurement cell which we are using in our project.”

The researchers plan to set out weathering noise barrier samples that were coated with reactive material at the A 4 interstate at Bergisch Gladbach. Prepared test samples will be measured at predetermined intervals in the measuring cell. The surface of the test sample is photo-catalytically active so it interacts with NOx once exposed to light.

During the next two years, the researchers will track the effectiveness of their method by measuring how much nitrous oxide is being removed. Aside gaining more data for precise results, this approach allows them to a solid basis to assume the longevity of the coatings.

The surfaces contain titanium dioxide catalysts, a material that is affordable and available in large quantities. When it is exposed to light, titanium dioxide catalyzes the nitrogen oxide into nitrate (NO3) – a compound of nitrogen and oxygen found in nature and in many food items in our diet.

I’ll have to mention a couple of potential downsides of the mentioned approach from the Fraunhofer IME researchers. While nitrate is generally harmful in low concentrations, high nitrate levels are known to interrupt the normal body processes of some infants. Nitrate becomes toxic when it is reduced to nitrite, a process that can occur in the stomach as well as in the saliva. Infants are especially susceptible because their stomach juices are less acidic and therefore are conducive to the growth of nitrate-reducing bacteria. The other potential major downside of the system is if the coating proves to be friable, since current studies claim that inhaled titanium dioxide dust could be carcinogenic.

If this approach does prove viable, the coatings could be applied onto larger surfaces, thus reducing NOx pollution in urban areas. The researchers also hope that a variation of this system could be used to purify the indoors air.

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