Photocatalytic products of the NO2 de-polluting process

MARÍA EUGENIA MONGE; BARBARA D'ANNA; CHRISTIAN GEORGE

Glasgow

Conferencia; SP3-Third International Conference on Semiconductor Photochemistry; 2010

Titanium oxide, TiO2, has become the material of choice in a variety of remediation processes due to its photocatalytic properties1,2 as well as its favourable physical and chemical properties.3 Many studies have recently focused on the development of environmental friendly materials by adding TiO2 to ordinary building materials such as concrete or by preparing TiO2 film coatings in order to deplete air pollutants, such as NOx.4-7 Although various photocatalytic materials are already on the market, very little reliable information is available, except for limited technical data, regarding their impact on air quality8 considering the potential formation of harmful intermediates. Recently, the photoenhanced NO2 uptake for real mineral dusts with HONO production was assigned to the chemistry occurring on the TiO2; and the photochemistry of nitrate doped dust samples was proved to be a potential renoxification process of the atmosphere.9,10 This work presents the study of the reactivity of irradiated TiO2 / SiO2 films with different TiO2 contents as proxies for de-polluting materials towards NO2. The influence of the photocatalyst concentration, the role of molecular oxygen and the effect of nitrate on the reactivity of TiO2 films were investigated. NO, HONO and nitrate are produced as a consequence of the NO2 loss on UV-illuminated TiO2 films. A renoxification pathway that involves the photochemistry of the NO3 radical leads to the release of NO, NO2 and of HONO from the TiO2 surface. The presence of O2 in the carrier gas modifies the NO and HONO production yields in the heterogeneous reaction between NO2 and TiO2 as well as the products of the renoxification process. These processes need to be considered further as potentially important in polluted urban atmospheres; taking into account the role of buildings, roads and natural materials in promoting heterogeneous reactions.11 1. A. Fujishima, T. N. Rao and D. A. Tryk, J. Photochem. Photobiol. C: Photochem. Rev., 2000, 1, 1-21. 2. S. Malato, P. Fernández-Ibáñez, M. I. Maldonado, J. Blanco and W. Gernjak, Cat. Today, 2009, 147, 1-59. 3. I. P. Parkin and R. G. Palgrave, J. Mater. Chem., 2005, 15, 1689-1695. 4. T. Maggos, J. G. Bartzis, M. Liakou and C. Gobin, J. Hazardous Mat., 2007, 146, 668-673. 5. N. Moussiopoulos, P. Barmpas, I. Ossanlis and J. Bartzis, Environ. Model. Assess. 2008, 13, 357-368. 6. F. Nakajima and I. Hamada, Catalysis Today, 1996, 29, 109-115. 7. H. Wang, Z. Wu, W. Zhao and B. Guan, Chemosphere, 2007, 66, 185-190. 8. K. Motohashi, T. Inukai and K. Toshimasa, RILEM Proceedings pro041, International Symposium on Environment-Conscious Materials and Systems for Sustainable Development, 2004, 27-34. 9. M. Ndour, P. Conchon, B. D'Anna, O. Ka and C. George, Geophys. Res. Lett., 2009, 36, 4. 10. M. Ndour, B. D'Anna, C. George, O. Ka, Y. Balkanski, J. Kleffmann, K. Stemmler and M. Ammann, Geophys. Res. Lett., 2008, 35, 5. 11. A. M. Rivera-Figueroa, A. L. Sumner and B. J. Finlayson-Pitts, Environ. Sci. Technol., 2003, 37, 548-554