International. Researchers from the Technical University of Vienna and the Polytechnic University of Marche in Italy developed a paint with nanoparticles that establish the power of self-cleaning.
Special titanium oxide nanoparticles are added to ordinary wall paint. These nanoparticles are photocatalytically active, which means that they can remove unwanted substances through sunlight. The wall makes the air cleaner and cleans itself at the same time.
A wide variety of pollutants occur in indoor air, from residues from cleaning agents and hygiene products to molecules that are produced during cooking or that are emitted by materials such as leather.
"For years, people have been trying to use custom wall paints to clean the air," says Professor Günther Rupprechter from the Institute of Materials Chemistry at UT Vienna. "Titanium oxide nanoparticles are particularly interesting in this context. They can bind and break down a wide range of pollutants."
Even so, simply adding ordinary titanium oxide nanoparticles to the paint will affect the durability of the paint. Even if pollutants are degraded by nanoparticles, they can also make the paint itself unstable, create cracks or even release volatile organic compounds, which can be harmful to health.
However, titanium oxide nanoparticles can clean themselves if irradiated with the right UV light, as titanium oxide is a photocatalyst.
UV radiation creates free charge carriers in particles, which induce the breakdown of airborne pollutants trapped in small parts and their release. This way, contaminants become harmless, as they don't stay stuck to the wall paint.
However, constantly irradiating a wall can become impractical.
"Our goal was to modify these particles in such a way that the photocatalytic effect can also be induced by ordinary sunlight," explains Günther Rupprechter.
This is accomplished by adding certain additional atoms to titanium oxide nanoparticles, such as phosphorus, nitrogen, and carbon. As a result, the frequencies of light that can be harvested by the particles change, and instead of just UV light, photocatalysis is then also triggered by ordinary visible light.
"We have now investigated this phenomenon in detail using a variety of different surface and nanoparticle analysis methods," says Qaisar Maqbool, the first author of the study. "In this way, we were able to show exactly how these particles behave, before and after they are added to the wall paint."
The research team mixed the modified titanium oxide nanoparticles with common, commercially available wall paint and rinsed a painted surface with a solution containing contaminants. Subsequently, 96% of pollutants could be degraded by natural sunlight. The color itself doesn't change, because the pollutants not only bind together, but also break down with the help of sunlight.
For the commercial success of such paints, it is also important to avoid expensive raw materials. "In catalysis, for example, precious metals such as platinum or gold are used. In our case, however, elements that are readily available everywhere are sufficient: To obtain phosphorus, nitrogen and carbon, we have used dried fallen leaves of olive trees, and the titanium for titanium oxide nanoparticles was obtained from metal waste, which is normally simply discarded," says Günther Rupprechter.
This new wall paint has among its advantages: removing pollutants from the air, greater durability and respect for production resources, since it can be obtained from recycled materials. Researchers continue to evaluate the product and study its commercialization.
