Scientists at the Fraunhofer Institute for Interfacial Engineering and Biotechnology in Germany are experimenting a lawn that can clean itself. They cover lawn furniture and other surfaces with a photocatalyitic coating of titanium dioxide and the molecules in it are "activated" by UV light causing them to go after organic molecules. Here's an explanation:
They act as a kind of catalyst, triggering an electrochemical reaction which produces free radicals. These and other active molecules strike a fatal blow to bacteria, fungi and similar organisms, first destroying the cell walls and then penetrating the cytoplasm – the substance that fills the cell – and damaging the bacteria's DNA. As a result, the organic substances are destroyed instead of remaining stuck to the surface.
And it works. In one test furniture using the coating was still clean after two years outside. The researchers are set to move on to the next step which is to develop coatings that can be activated by artificial light.