Analisis

Building and Environment 44 (2009) 2463–2474

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Building and Environment
journal homepage: www.elsevier.com/locate/buildenv

Experimental study of photocatalytic concrete products for air purification
¨ G. Husken*, M. Hunger, H.J.H. Brouwers
Department of Civil Engineering, Faculty of Engineering Technology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands

a r t i c l e i n f o
Article history: Received 4 March 2009 Received in revised form 17 April 2009 Accepted 22 April 2009 Keywords: Air purification Heterogeneous photocatalysis Titanium dioxide Nitrogen oxides Concrete paving blocks

a b s t r a c t
Air quality in inner-city areas is a topic which receives much attention nowadays but in the coming years, theoverall 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 ratesespecially for diesel powered passenger cars and freight vehicles. A promising approach for solving the problem of nitrogen oxides (NOx) 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 andtheir 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 ofnitric 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 anddirect 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. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction Air pollution caused by road traffic and industry is one of the majorproblems in metropolitan and urban areas. Despite intensifying emission control requirements (e.g. [5]) and the increased installation of emission reduction systems, the air pollution and in particular the pollution by nitric oxides (NO) from diesel engines will remain a serious issue in the near future (cp. Table 1). The by far largest emissions are generated by local traffic and industrial flue gases(cp. Fig. 1). In this respect, attempts regarding the active reduction of NO can be found in forms of filter devices for industrial stacks (denitrogenization – DENOX plants) or active filter systems for e.g. ventilation outlets of tunnels. According to Matsuda et al. [18], a further solution is the photocatalytic oxidation of nitrogen oxides (NOx) to low concentrated nitrates. The accruing reaction* Corresponding author. ¨ E-mail address: g.husken@ctw.utwente.nl (G. Husken). 0360-1323/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2009.04.010

products in form of nitrate compounds are water soluble and will be flushed from the active concrete surface by rain. The nitrate compounds can be subsequently extracted from the rain water by a standard...