Nitrogen dioxide removal and nitrous acid formation on titanium oxide surfaces—an air quality remediation process?

The reactivity of NO2 on irradiated TiO2/SiO2 films was studied, with different TiO2 contents, as proxies for NOx de-polluting materials. 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 anions are produced as a consequence of the NO2 loss on UV-illuminated TiO2 films. The photoinduced nitrate conversion into NOx and HONO at the TiO2 surface is discussed as being a renoxification process, which involves the NO3 radical. 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. Depending on the nature of the surface, the interaction between NO2 and nitrate with TiO2 may generate HONO that may have a negative impact on air quality.