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Coating Research Improves IAQ

Wednesday, December 9, 2015

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Research undertaken at a Swedish university proposes a cure for “sick building syndrome” that uses coatings to take on the treatment process.

Bozhidar Stefanov, a student at Sweden’s Uppsala University, built his dissertation on the concept that a nanostructured coating based on titanium dioxide (TiO2), when applied to window glass, could utilize sunlight to help clean the building’s air.

Uppsala University
Uppsala University

Research at Uppsala University looks at the ways a nanostructured coating based on titanium dioxide could, when applied to window glass, utilize sunlight to help clean the building’s air.

Stefanov’s thesis shows how the preparation of such coatings, tailor-made for indoor air cleaning, can be made more effective, the university announced Monday (Dec. 7) in a statement.

Treating Sick Building Syndrome

Harmful organic molecules in indoor air can cause the unpleasant health effects (headaches, eye or skin irritation, respiratory issues), known as sick building syndrome, experienced by workers in office environments with inadequate ventilation and poor indoor air quality.

Contributors include flaws in the HVAC systems, contaminants from the outgassing of some types of building materials, volatile organic compounds molds, or use of light industrial chemicals.

While current methods to clean the air require manpower, energy and upkeep, Stefanov’s solution uses glass with a TiO2-based nanostructured coating that uses sunlight to remove organic pollutants from indoor air by passing it between the inner panes of the window.

Harnessing the Power of TiO2

Titanium dioxide is a white pigment often used in paints, toothpastes and sunscreens. In the form of nanoparticles, it obtains special properties that make it chemically very reactive.

It efficiently absorbs ultraviolet light and uses this energy to destroy organic molecules at its surface in a process called photocatalysis.

This has made titanium dioxide the ‘”white knight” of nanotechnology, according to Uppsala, as well as the photocatalyst of choice for water and air cleaning.

istock/Thomas Abraham
© iStock.com / Thomas Abraham

Harmful organic molecules in indoor air can cause the unpleasant health effects known as sick building syndrome, experienced by workers in office environments with poor indoor air quality.

Recently, pavement blocks of TiO2-impregnated cement have been used to mitigate outdoor air pollution in cities, including a field trial conducted in Malmö, Sweden.

Striving for Cleaner Indoor Air

In the Division of Solid State Physics at the Ångström Laboratory of Uppsala University, researchers, led by Stefanov, are striving to harness the photocatalysis effects described above to clean indoor air.

Using an industrial process called “magnetron sputtering,” the team deposited nanostructured surface coatings of TiO2 onto window glass.

The transparent coatings, which are a hundred times less thick than a human hair, have been shown to be very effective for removing acetaldehyde, a common indoor air pollutant.

Manipulating Facets

Windows comprising of such titanium-dioxide-coated glass can be used to clean air indoors, but there is one problem, the team noted. Normally, pollutant decomposition products bind strongly to the photocatalyst surface and block active sites, thereby leading to loss of photocatalytic activity.

In his thesis, Stefanov shows that the exposed crystalline facets of the nanoparticles comprising the coating give sputter-deposited coatings an advantage.

Just like the dice used in gaming, not all sides of the TiO2 nanoparticles are equal in their reactivity—some of their crystalline facets are much more active in photocatalysis than others, Stefanov noted.

Unfortunately, these active facets correspond to only about 10 percent of the nanoparticle surface, so in coatings made of randomly oriented nanoparticles it is very difficult to strike a “lucky six,” he said, and have the reactive facets exposed at the film surface.

During the project, Stefanov found a way to tweak the deposition of sputter-deposited TiO2 films in order to “cheat the dice” and have a high probability of the very reactive TiO2 facets at the surface.

These preferentially oriented coatings exhibit not only higher activity against air pollution, but their activity is also less dependent on external conditions such as humidity and temperature.

Additionally, he found that if the surface of such preferentially oriented TiO2 coatings is made acidic by attachment of sulfate molecules, they become even more resistant to deactivation.

Bringing these new findings together—preferential nanocrystal orientation, sulfate modification, and controlled humidity and temperature—Stefanov has realized a new principle for a photocatalytic window with sustained air cleaning activity, the university announced, an important step forward to improve indoor air.

Stefanov is scheduled to defend his dissertation on Dec. 11.


Tagged categories: Coatings Technology; Colleges and Universities; Indoor air quality; Research and development; Titanium dioxide

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