Self-cleaning wall paint developed
A research team from TU Wien and Università Politecnica delle Marche has developed special titanium oxide nanoparticles with self-cleaning properties that can be incorporated into wall paints.
The beauty and whiteness of white wall paints are not permanent. Often, airborne substances accumulate on the paint surface. While this can be a desirable effect as it temporarily cleans the air, over time the color changes and the paint needs to be renewed. A research team from TU Wien and Università Politecnica delle Marche (Italy) has succeeded in developing special titanium oxide nanoparticles with self-cleaning properties that can be incorporated into commercially available wall paints. The photocatalytically active nanoparticles use sunlight not only to bind airborne substances but also to subsequently break them down. The wall becomes cleaner air and cleans itself at the same time. As raw material for the new wall paint, metal scraps and dried leaves that would normally be discarded under normal conditions were used. The study was published in ACS Catalysis journal.
Modified titanium oxide in wall paint
In interior spaces, various contaminants are present, ranging from residues of cleaning products and hygiene products to molecules produced during cooking or emitted from materials such as leather. In some cases, this can lead to health problems referred to as sick building syndrome. On the subject, Prof. Günther Rupprechter from the Institute of Materials Chemistry at TU Wien says, "People have been trying to use specialized wall paints to clean air for years. Titanium oxide nanoparticles are particularly interesting in this context. They can bind and break down a wide variety of contaminants." However, adding ordinary titanium oxide nanoparticles to paint can affect the paint's durability, as contaminants are broken down by the nanoparticles, making it itself unstable and causing cracks. In the worst case, volatile organic compounds can be released, which can be harmful to health. After a certain time, the paint layer turns gray and becomes discolored; eventually it needs to be renewed.
Self-cleaning by light
On the other hand, nanoparticles can clean themselves when exposed to UV light. Titanium oxide is a material called a photocatalyst that enables chemical reactions when exposed to appropriate light. UV radiation creates free charge carriers in the particles, causing trapped contaminants in the air to break down into small fragments and be released. In this way, contaminants are rendered harmless but do not remain permanently bound to the wall paint. The wall color remains stable in the long term. In practice, this has little benefit because repeatedly irradiating the wall with intense UV light to drive the self-cleaning process is an inconvenient procedure. Rupprechter says, "Therefore, our goal was to modify these particles so that the photocatalytic effect can also be activated by ordinary sunlight." This was achieved by adding certain additional atoms such as phosphorus, nitrogen and carbon to the titanium oxide nanoparticles. As a result, the light frequencies that can be collected by the particles change and photocatalysis can be activated not only by UV light but also by normal light.
96 percent less contaminant
Qaisar Maqbool, first author of the study, says, "We investigated this phenomenon in considerable detail using various different surface and nanoparticle analysis methods. In this way, we were able to show exactly how the particles behave before and after they are added to the wall paint." The research team mixed the modified titanium oxide nanoparticles with commercially available ordinary wall paint and rinsed the painted surface with a solution containing contaminants. Subsequently, it was found that 96 percent of the contaminants could be broken down by natural sunlight. The color itself does not change because the contaminants are not only bound but are also broken down with the help of sunlight.
Waste as raw material
To achieve commercial success with such paints, it is also important to avoid expensive raw materials. Rupprechter says on the subject: "For example, precious metals such as platinum or gold are used in catalysts. But in our case, we used dried fallen leaves from olive trees to obtain sufficient phosphorus, nitrogen and carbon, which are easily found everywhere, and titanium for the titanium oxide nanoparticles was obtained from metal scraps that are normally simply discarded." This new type of wall paint combines multiple advantages at the same time; it cleans contaminants from the air, lasts longer than other paints and provides greater resource savings in production since it can be obtained from recycled materials. Further experiments are underway and commercialization of the wall paint is planned.
Academic Reference: Qaisar Maqbool et al, Highly Stable Self-Cleaning Paints Based on Waste-Valorized PNC-Doped TiO2 Nanoparticles, ACS Catalysis (2024). DOI 10.1021acscatal.3c06203
