Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World

by Mark Miodownik

Many new versions of concrete have been invented to refresh its aesthetic appeal. The latest is self-cleaning concrete, which contains titanium dioxide particles. These sit on its surface but are microscopic and transparent, so it looks no different. However, when they absorb UV light from the sun, the particles create free radical ions, which break down any organic dirt that comes into contact with them. The remains are washed away by the rain or blown away by the wind. A church in Rome called Dives in Misericordia has been constructed with such self-cleaning concrete. In fact, the titanium dioxide does more than clean the concrete: it can also reduce the level of nitrogen oxide in the air, produced by cars, like a catalytic converter. Several studies have shown that this works, and open up the possibility that in the future buildings and roads may not be purely passive; they may purify the air much like plants.