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

The reactivity of NO(2) on irradiated TiO(2)/SiO(2) films was studied, with different TiO(2) contents, as proxies for NO(x) de-polluting materials. The influence of the photocatalyst concentration, the role of molecular oxygen and the effect of nitrate on the reactivity of TiO(2) films were investigated. NO, HONO and nitrate anions are produced as a consequence of the NO(2) loss on UV-illuminated TiO(2) films. The photoinduced nitrate conversion into NO(x) and HONO at the TiO(2) surface is discussed as being a renoxification process, which involves the NO(3) radical. The presence of O(2) in the carrier gas modifies the NO and HONO production yields in the heterogeneous reaction between NO(2) and TiO(2) as well as the products of the renoxification process. Depending on the nature of the surface, the interaction between NO(2) and nitrate with TiO(2) may generate HONO that may have a negative impact on air quality.