Talk about your metamaterials. Unhappy working only on the inside, the walls of a Roman church have been discovered cleaning the outside air, according to The Long Now Foundation. It's believed that the titanium dioxide material specified for the concrete walls of the church have photocatalytically reacted with nitrogen oxide pollutants in the atmosphere, resulting in fewer pollutants overall.
A similar coating is being investigated for urban sidewalks and roads.
If you check out the link, take a look at the dateline for the post, which reads "January 14th, 02009." The Long Now Foundation and the church share a similar and lengthy timeline.