A water pipe that purifies its contents as it flows? A coating that breaks down air pollutants as they flow by? A surface that disinfects itself and keeps itself clean? What sounds like science fiction becomes possible with the photocatalyst titanium dioxide. Under UV light, titanium dioxide is able to purify air and water, kill bacteria on its surface and break down fats. Although these properties have been known since the 1970s, the breakthrough of photocatalytically active titanium dioxide is...