For many people, the onset of warmer weather can mean pulling out the ol' scrubbing brush and getting to work on the slimy film of moss, algae, fungi and bacteria that has built up on the garden furniture over the colder months. But we may soon be able to say goodbye to this tiresome chore thanks to researchers at Fraunhofer who are developing coatings that would be activated by the sun’s rays to destroy organic substances attaching themselves to various surfaces.

The photocatalytic coatings being developed at the Fraunhofer Institute for Thin Films and Surface Engineering (IST) incorporate titanium dioxide molecules that are "activated" by the UV light in the sun’s rays to produce free radicals in an electrochemical reaction. These free radical molecules destroy the cell walls of bacteria, fungi and similar organisms before penetrating the cytoplasm and damaging the organism’s DNA.

The Fraunhofer researchers set out to discover just what kind of organic elements these photocatalytic coatings were effective against. Dr. Iris Trick, group manager at the Fraunhofer Institute for Interfacial Engineering and Biotechnology (IGB) in Stuttgart ran outdoor tests on plastic garden chair armrests with and without the coating.

They first sprayed the coated and uncoated armrests with a mixture of various bacteria, mosses, algae and fungi and then left them exposed to the weather for two years. After this period the team says it was almost impossible to remove the layer of dirt from the uncoated armrests, while the coated armrests remained almost completely clean and white.

In the lab, the researchers also tested the effectiveness of the coatings on a range of other surfaces. They applied up to 30 different kinds of fungal, bacterial and algal cultures to coated and uncoated surfaces and compared how they evolved. The results indicated the potential applications for the photocatalytic coatings extend far beyond garden furniture armrests.

Ten Fraunhofer Institutes have now joined forces to form the Fraunhofer Photocatalysis Alliance to explore various avenues for the technology.

One team is looking to put titanium dioxide molecules to work in paints that could be applied to building facades that would stay reasonably clean when exposed to sunlight. Another team has developed a self-cleaning coating for glass surfaces that could be used on displays, such as smartphone screens.

"If you apply a thin coating of titanium dioxide to a glass surface such as a smartphone screen, the skin oils and fingerprints gradually disappear from the display by themselves," says Dr. Michael Vergöhl, head of department at the Fraunhofer IST.

Unlike previous photocatalytic surfaces that would need to sit in the sun for up to three days to work their self-cleaning magic, the new coating only requires one hour of sunlight. The researchers say the next step is to develop materials that can also be activated by artificial light.

Source: Fraunhofer

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