Beautiful white wall paint does not stay beautiful and white forever. Often, various substances from the air accumulate on its surface. This can be a desired effect because it makes the air cleaner for a while -- but over time, the color changes and needs to be renewed. Now, special titanium oxide nanoparticles have been developed that can be added to ordinary, commercially available wall paint to establish self-cleaning power: The nanoparticles are photocatalytically active, they can use sunlight not only to bind substances from the air, but also to decompose them afterwards.