Radiolysis of aqueous nitrate solutions

Abstract

The radiolysis of aqueous nitrate ion solutions was studied as a function of the concentration in the presence of air, oxygen and hydrogen at different concentrations. In dilute solutions, NO–3 is reduced to NO2 by hydrated electrons and H atoms. OH radicals oxidize the NO–2 formed. In the presence of oxygen at relatively low concentrations of NO–3, NO2 reacts with HO2. Primary yields of e–aq, H, OH and H2 O2 were determined for the range of 10–3–10–1 M NO–3, GR=Ge–aq+GH increased from 3.21 to 3.46 accompanied by a corresponding decrease of GH2. The observed yields of GOH= 2.62 ± 0.03 and of GH2O2= 0.73 ± 0.02 were independent of NO–3 concentration. For higher NO–3 concentrations a linear increase of the total yield GR+ 2GH2 was observed. This phenomena may be interpreted as the formation of NO–2 and OH radicals by subexcitation electrons, which otherwise would form molecular hydrogen or hydrated electrons. Above 1 M, nitrate decomposes by “direct action” to give nitrite. The yield of “molecular” hydrogen decreases with increasing nitrate concentration, whereas the yields of hydrogen peroxide remains constant with a G(H2O2)= 0.75 ± 0.02 over the whole concentration range up to 5 M. Oxygen 18-enriched nitrate ions in H2O16 and H2O18 used to determine the origin of the hydrogen peroxide at high NO–3 concentration, show that the part of H2O2 which originates from the decomposition nitrate ion by direct action is directly proportional to the fraction of energy absorbed by these ions.