VUV-photolysis of aqueous solutions of hydroxylamine and nitric oxide. Effect of organic matter: phenol

Abstract

VUV-irradiation of aqueous solutions containing hydroxylamine (NH₂OH) in its acid form (NH₃OH⁺) and phenol (C₆H₅OH) results in the simultaneous mineralization of the organic substrate and the almost quantitative reduction of NH₃OH⁺ to ammonium ions (NH₄⁺). Irradiation of aqueous solutions of NH₃OH⁺ in the absence of organic substrates showed the formation of nitrate (NO₃⁻) and nitrite (NO₂⁻) and minor quantities of NH₄⁺. In line with these experiments, VUV-irradiation of aqueous solutions of nitrogen monoxide (NO˙) yields NH₄⁺ only when C₆H₅OH is simultaneously mineralized. A possible reaction mechanism is discussed, where reactions of NO˙ and NH₃OH⁺ with hydrogen atoms (H˙), hydroxyl radicals (HO˙) and hydrated electrons (e⁻_aq), all generated by the VUV-photochemically initiated homolysis of water, are of great importance to the observed results. In the presence of phenol, competition between phenol and either NO˙ or NH₃OH⁺ for these reactive intermediates in the primary volume of reactions strongly determines the oxidation state and nature of the N-containing products. C-Centered radicals and intermediate products of reactions may also have an important effect on the overall mechanism. The present results are discussed in relation to the actual state of knowledge presented in the literature.