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

Abstract

The reactivity of NO₂ on irradiated TiO₂/SiO₂ films was studied, with different TiO₂ 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 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 NO_x 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.