Heterogeneous Photocatalysis Applied to Concrete Pavement for Air Remediation

MARÍA DE LOS MILAGROS BALLARI; MARTIN HUNGER; GÖTZ HÜSKEN; JOS H.J.H. BROUWERS

Praga (República Checa)

Simposio; 3rd International Symposium on Nanotechnology in Construction; 2009

Heterogeneous photocatalysis represents an emerging environmental control option for the efficient removal of chemical pollutants and it can be applied to water and air purification. This process involves a nano-solid semiconductor catalyst, regularly titanium dioxide (TiO2), which is activated with ultraviolet light of the appropriate wavelength. Nitrogen oxides (NOx) is the generic term for a group of highly reactive gases, most of them emitted in air in the form of nitric oxide (NO) and nitrogen dioxide (NO2). Nitrogen oxides form when fuel is burned at high temperatures, as is the case in combustion processes in automobiles. NOx causes a wide variety of health and environmental impacts, like the formation of tropospheric ozone and urban smog through photochemical reactions with hydrocarbons. Furthermore, NOx together with SOx (sulfur dioxide and sulfur trioxide) is the major contributor to the “acid rain”, one of the most serious environmental problems across the world. The European Union (EU) has taken important steps over the past decade leading to a decrease in the emissions to air and water of a number of pollutants. One of its directives (1999/30/EC) establishes limit values for concentrations of sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. Some of the pollutant emissions have since become more or less manageable, although particulates, NOx and smog are still problematic. The development of innovative materials that can be easily applied on structures, with both de-soiling and de-polluting properties, is a significant step towards improvements of air quality. The use of TiO2 photocatalyst in combination with cementitius and other construction materials has shown a favorable effect in the removal of nitrogen oxides. In the present work the degradation of NOx compounds employing concrete paving stones with TiO2 to be applied in road construction is studied. The experiments were carried out in a photoreactor designed according to the pre-standard ISO TC 206/SC N (2004) to assess these kind of photocatalytic materials. A kinetic model is proposed to describe the photocatalytic oxidation of NOx and the influence of several parameters that can affect the performance of these stones under outdoor conditions, such as irradiance, relative humidity and wind speed.