With gold nanoparticles against smog

Newly developed material decomposes volatile organic compounds

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In addition to nitrogen and sulfur oxides, many volatile organic compounds (VOCs) in the air contribute to smog and increased ozone levels, and can harm human health. Scientists have now developed a material that can effectively remove and decompose these VOCs from the air: Porous manganese oxide garnished with gold nanoparticles.

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Most of today's emission control systems based on photocatalysts, adsorbents such as activated carbon or a so-called ozonolysis. However, these classic systems do not degrade organic pollutants at room temperature very well.

The material of the Japanese researchers now releases the air very effectively from VOCs as well as nitrogen and sulfur oxides already at these values. As reported in the journal Angewandte Chemie, this is a highly porous manganese oxide, in which gold nanoparticles are virtually ingrown.

First tests successful

To test the performance of their new catalyst, the team led by Anil K. Sinha of the Toyota Central R & D Labs performed tests on acetaldehyde, toluene and hexane, three major components of organic air pollution, both indoor and outdoor. All three pollutants were very effectively removed from the air and degraded on the catalyst - much better than with conventional catalyst systems. display

On the one hand, the secret to the success of the new material is the extremely high inner surface of the porous manganese oxide - higher than with all previously known manganese oxide materials. It offers the volatile molecules a large number of adsorption sites. On the other hand, the adsorbed pollutants are degraded very effectively. Apparently, oxygen from the manganese oxide lattice is available for oxidation processes.

The degradation on the surface is very effective, as there are free radicals on the surface. Presumably, oxygen dissociates from the air at the gold surface and can replenish the free lattice sites from there.

Gold particles penetrate deep into the surface

This process works only if the material is produced in a specific way: The gold must be deposited on the manganese oxide by means of so-called vacuum UV laser ablation. In this method, a gold surface is irradiated with a special laser, which removes gold particles by evaporation.

These gold particles have an exceptionally high energy, allowing them to penetrate comparatively deep into the surface of the manganese oxide. Only then can the manganese oxide carrier and the tiny gold lumps interact sufficiently well.

(idw - Society of German Chemists, 03.04.2007 - DLO)