Construction Materials Detoxify Pollutants

Construction Materials Detoxify Pollutants

Smart construction materials and coatings that capture and decontaminate air pollutants are being developed in Europe. In the presence of sunlight, plaster, mortar, concrete, and coatings containing titanium dioxide can change the chemical composition of the pollutants, which are then washed harmlessly away.

The performance of these materials is being tested by a European consortium of private companies, research institutions, and the European Commission's Joint Research Centre (JRC) as part of a program for innovative construction materials to help in the fight against air pollution. While tests are still underway, some preliminary results in the field already demonstrate that the photo-catalytic process works to reduce pollution.

In 2002, after 7,000 square metres of road surface in Milan, Italy, were covered with a photo-catalytic cement material, there was up to 60 percent reduction in the concentration of nitrogen oxides at street level, researchers report.

Currently, several photo-catalytic processes using the new materials and coatings are being stud-ied at the INDOORTRON test facility in Ispra, Italy, a facility of the Physical and Chemical Exposure Unit of the JRC's Institute for Health and Consumer Protection.

Here EU scientists are measuring the efficiency of the coatings in breaking down mixtures of pollutants, which contribute to the formation of smog.

"Smart coatings can cause a revolution, not only in the management of air pollution but also in how architects and town planners tackle the persistent problem of urban smog," says European Research Commissioner Philippe Busquin.

The new materials and coatings are being developed as part of the Photo-catalytic Innovative Coverings Applications for De-pollution Assessment (PICADA) project, which Busquin says is very useful in bringing public and private sectors together in Europe.

"The PICADA project itself is closely linked to the remit of our program for competitive and sustainable growth," he said, "and fosters strong collaborative ties with various different European businesses."

The titanium dioxide smart construction materials are being tested under experimental conditions of humidity, temperature, and ultraviolet (UV.) radiation, to simulate a real world setting.

The de-pollution properties of these materials are based on the semi-conducting photo-catalytic titanium dioxide (TiO2). The coatings containing TiO2 are effective because air turbulence constantly carries NOx and other volatile and semi-volatile compounds over the surface of the buildings. The molecules stick to the surface long enough for the oxidation process to break them down.

The process is a simple one. Nitrogen oxide (NOx) gases and organic compounds diffuse through the porous surface and stick to the titanium dioxide nano-particles of the construction materials and coatings.

Absorption of UV. light by the incorporated titanium dioxide (TiO2) leads to its photo-activation, and then the activated TiO2 degrades the pollutants absorbed onto the particles.

The acidic products created by this process are washed away by rain and/or neutralized by alkaline calcium carbonate contained in the materials.

The innovative materials developed by the consortium have yet to be applied outside of laboratory testing conditions. But preliminary tests with similar photo-catalytic materials under field conditions show that air quality can be improved.

Construction undertaken in Japan using photo-catalytic cements and paving slabs that do not contain TiO2 have shown a marked decline in air pollution.

Coating materials designed on the basis of titanium oxide are even better, researchers say, because they can cover a much greater surface than cement, since buildings and street furniture can be covered or painted with them.

The new construction materials should help to reduce levels of nitrogen oxides (NOx gases) which cause respiratory problems and trigger smog production, and of other toxic substances such as benzene.

The whole project will cost $3.4 million (U.S. $4.2 million) and the European Commission is funding up to $1.9 million (U.S. $2.34 million).

The European Commission is already thinking of these new construction materials and coatings to help meet the European Union target of reducing NOx levels to under 21 parts per billion per year by 2010.

To date, European researchers have focused on the development of smart materials for outdoor applications. Going forward, they will investigate whether these products can be used as de-polluting building materials and coatings indoors as well.

The demand for TiO2 has been increasing worldwide, according to the UK's Millenium Chemicals, the second largest titanium dioxide producer in the world and one of the PICADA project partners. If the smart materials tests prove successful, the demand will rise still higher.

Titanium is a mineral found in sands in several African countries and in Australia. Environmentalists warn the mining of titanium produces acid and can poison nearby water bodies.

Source: Environment News Service (ENS).