This paper deals with the degradation of NO by photocatalytic oxidation using TiO 2 -based coatings. Tests are conducted at a laboratory scale through an experimental setup inspired from ISO 22197-1 standard. Various parameters are explored to evaluate their influence on photocatalysis efficiency: TiO 2 dry matter content applied to the surface, nature of the substrate, and illumination conditions (UV and visible light). This article points out the different behaviors between three kinds of substrates which are common building materials: normalized mortar, denser mortar, and commercial wood. The illumination conditions are of great importance in the photocatalytic process with experiments under UV light showing the best results. However, a significant decrease in NO concentration under visible light is also observed provided that the TiO 2 dry matter content on the surface is high enough. The nature of the substrate plays an important role in the photocatalytic activity with rougher substrates being more efficient to degrade NO. However, limiting the roughness of the substrate seems to be of utmost interest to obtain the highest exposed surface area and thus the optimal photocatalytic efficiency. A higher roughness promotes the surface contact between TiO 2 and NO but does not necessarily increase the photochemical oxidation.

Air pollution is a serious public health concern in France and many other countries. Nitrogen oxides (NO x) include nitrogen monoxide (NO) and nitrogen dioxide (NO 2). They are mainly outdoor pollutants produced during combustion of fossil fuel. These gases can easily infiltrate buildings and thus increase indoor pollution. The recommended guideline values for NO 2 are 200 µg/m 3 (short-term exposure) and 40 µg/m 3 (long-term exposure). Although no guideline values exist for NO, this gas can be oxidized by atmospheric ozone and thus produce NO 2. This paper studies the depollution efficiency of photocatalysis towards indoor NO. Experiments were conducted at real scale, in a 10-m 3 experimental chamber developed at the LMDC and used as a reactor. The interior walls of the chamber were equipped with painted plasterboards treated with photocatalytic coating (3 g/m² of TiO 2). Gas was continuously injected into the chamber according to a specific procedure: (1) pollutant injection at high flow rate to reach 200 ppb of NO, (2) pollutant injection at low flow rate in order to keep the NO concentration constant at 200±10 ppb, and (3) photocatalysis activation by switching on the light. Typical indoor lighting systems (fluorescent tubes, LED and halogen bulbs) were tested and UV fluorescent tubes were also used to optimise the photocatalytic efficiency. Results showed that NO indoor concentration was reduced by photocatalysis in real-world conditions. Significant NO degradation was obtained under visible light. In addition, using the experimental procedure presented in this paper, a new method for evaluating air depollution efficiency by photocatalysis at real scale is proposed.

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