Experimental study of photocatalytic concrete products for air purification

Air quality in inner-city areas is a topic which receives much attention nowadays but in the coming years, the overall interest on this topic will become even bigger. One major concern is caused by the reduction of the limiting values given by the European Council Directive 1999/30/EC [Relating to limit values for sulphur dioxide, nitrogen dioxide and oxides of nitrogen, particulate matter and lead in ambient air. Official Journal of the European Communities 1999, L 163/41–60] and increasing traffic rates especially for diesel powered passenger cars and freight vehicles.A promising approach for solving the problem of nitrogen oxides (NO_x) is the photochemical conversion of nitrogen oxides to low concentrated nitrates due to heterogeneous photocatalytic oxidation (PCO) using titanium dioxide (TiO₂) as photocatalyst. A variety of products containing TiO₂ are already available on the European market and their working mechanism under laboratory conditions is proven. However, there is still a lack of transforming the experimental results obtained under laboratory conditions to practical applications considering real world conditions.This paper presents the research conducted on photocatalytic concrete products with respect to the evaluation of air-purifying properties. The degradation process of nitric oxide (NO) under laboratory conditions is studied using a test setup for measuring the performance of photocatalytic active concrete products. The test setup uses the UV-A induced degradation of NO and is oriented on the ISO standard ISO 22197-1:2007. Besides the introduction of the test setup, a uniform measuring procedure is presented to the reader which allows for an evaluation and direct comparison of the performance of photocatalytic active concrete products. This kind of direct comparison was not possible so far. Furthermore, the results of a comparative study on varying photocatalytic concrete products of the European market will be discussed.