Clean the air with ice

An air purifier can be cleaned in the Netherlands.

Stone of Dutch researchers promise clean air - Photo: CNET

Researchers at the University of Twente are building a special stone road in the town of Hengelo, in the province of Overijssel, according to the CNET website. As a result, the surface of the stone can turn nitrogen oxide (NOx) from car smoke into harmless nitrate. NOx is a substance that can cause rain or haze, and Dutch scientists are hoping to contribute to solving the problem by doing so. Jos Brouwers, head of the research team, said the stone could handle 30-40% of the NOx that is "discharged" into them.

The test stone contains a layer of titanium dioxide photocatalyst. This substance uses sunlight to "treat" NOx. The basic principle is that the photons from ultraviolet light activate titanium dioxide. OH ions are released and they react with NOx to form nitrate salts "on" the rock surface. This salt will be cleaned when it rains and does not pollute the water.

Brouwers said the idea of making clean air was developed by Japanese people 10 years ago. However, in the formulation of the Japanese, the density of titanium dioxide is too high so the stone is expensive. According to Brouwers, his team has established a superior titanium density, which can reduce production costs by 30% compared to Japanese.

Dutch researchers have tested the 10 cm x 20 cm road pavement in the laboratory by blowing NOx-enhanced air through the rock surface and providing an artificial ultraviolet light source. There were two road sections in the test in Hengelo, a plain lined stone and an air-purifying stone. Air quality will be measured on each segment to determine the effect of particular stones. Road construction will be completed later this year. Measurement activities will be conducted early next year and the first results are expected to be released in the summer of 2009.