| Ambient NOx are originated from the combustion of fossil fuels in presence of N2 and O2, which promotes the so-called urban smog and ozone formation that have severe health impacts. Nevertheless, many cities in Europe, and namely in Portugal, are still recording NOx concentrations above the legislated limit (2008/50/EC). Therefore, technologies are required to solve this environmental problem, among which photocatalysis should play an important role.;Photocatalysis uses energy of light and a catalyst, generally nanoparticulate TiO2 (photocatalytic TiO2; herein called photo-TiO 2), to promote chemical reactions. However, appropriate supports for TiO2 are required. Construction materials can be used to support photocatalytic TiO2 for the photoabatement of atmospheric pollutants. From all possible construction materials, paint coatings present interesting advantages since almost all surfaces can be painted and their low thickness allow the use of low amounts of photocatalyst, for the same abatement capacity.;An exterior, water-based, high quality paint was selected as starting paint for the work presented in this thesis. From this paint, half of the pigmentary TiO2 (that promotes paint opacity) was replaced by different commercially available photocatalytic TiO2 (9 wt.%, wet based); when incorporating P25 photocatalyst this paint was named reference paint. Part II of this dissertation focuses on the photoactivity study of paints incorporating different commercially available photocatalysts, and powder pressed films made by each photocatalyst. It was concluded that the ranking of the best photoactive paint films did not match with the ranking of the best photoactive powder pressed films.;Therefore, the influence of paint film components on the photoactivity of P25 photocatalyst was consequently studied - Part III of this dissertation. Powder films, containing only powder (mostly inorganic) paint components, and pseudo-paint films, containing also part of the organic components, were prepared mixing stepwise components of the reference paint. It was concluded that pigmentary TiO2 absorbing competitively the UV light, was the most critical component affecting the photocatalytic activity. Films also containing different organic components, which are added in proportions accordingly to the reference paint recipe, show different transient periods. However, similar steady state photoactivities were achieved. This was ascribed to the photoerosion of a significant fraction of the organic phase during the transient period. Powder components play a major role on light behavior of films and such fact rules the long-term photoactivity; in fact, films containing the same powder matrix but different organic composition, show the same photoerosion (ca. 25 wt.%) and therefore the very similar photoactivity.;Deposition of photocatalytic TiO2 particles either on the internal or external surface of porous solid inorganic adsorbent materials, such as zeolites, are possible approaches for the protection of the paint matrix. If particles are deposited inside the pore structure, one can achieve paint protection avoiding direct contact of the paint matrix, namely the binder, with the photocatalytic TiO2 particles; harmful gases can yet penetrate the support pore system and get oxidized. On the other hand, if photocatalytic TiO2 particles are deposited on the outer surface of the support, protection can still occur once direct contact of paint and TiO2 is reduced (dilution effect). Chapters 5 and 6 report the study of photocatalytic TiO2 produced by ion exchange and impregnation on different supports, respectively. The highest photoactivity was observed for the TiO2 supported on the outer surface of zeolite Y. |
