Photochemistry of aqueous nitrate solutions excited in the 195-nm band

Abstract

The photochemistry of aqueous nitrate solutions excited in the high-energy (195-nm) mr* band of the ion is investigated using steady-state and flash-irradiation techniques. The formation of hydroxyl radicals is demonstrated by observing the absorption of characteristic transients formed by the reaction of O H (or 0-) with C082-, CNS-, and 02. T h e formation of pernitrite is also investigated and found t o be unaffected by [NO2-], [NOI-], [02], and [CH,CH20H]. The flash technique enables the determination of the dissociation constant of pernitrous acid, yielding pK, = 6.0 =t 0.3. A third photochemical path, the evolution of 02 and the stoichiometric formation of NOz-, is also investigated. T h e effect of various solutes on the yields of molecular oxygen is analyzed, The results appear to be inconsistent with a mechanism involving intermediate oxygen atoms.

Photoinduced decomposition of nitrate in drinking water in the presence of titania and humic acids

“…The positive influence of the humic acids on the conversion of nitrate could have its origin in the increase of the pH upon addition of the humic acids. Other authors [3,6,31] observed an increase in the rate of formation of nitrite with increased pH. It is not possible to distinguish from our data whether the effect of the humic acids is a consequence of the change in pH, or of reactive species formed from humic acids under irradiation, i.e.…”

“…Kudo et al [18] irradiated 1M NaNO 3 and 1M HNO 3 , respectively, in experiments similar to ours and observed the formation of nitrite with a rate of 0.3 µmol/h in both cases. An increasing rate of formation of nitrite with increasing pH in the range of 5 to 8 was reported by Daniels [5], Wagner [6], Warneck [7], and Shuali [31]. Photoreduction of nitrate to nitrite has also been applied for the quantitative analysis of nitrate [32,33], with an increased reduction efficiency at increased pH.…”

“…Further investigations [3][4][5][6]30,31] yielded inconsistent results regarding a nitrate/nitrite equilibrium [3,4] and regarding the product distribution which besides nitrite has been reported to include oxygen atoms [3,5], molecular oxygen [6,31], hydrogen peroxide [6], hydroxyl radicals [31], peroxynitrate [6], and pernitrite [31]. In Warneck's more recent investigations [7] two pathways of nitrate photodecomposition are suggested, one giving nitrite and oxygen atoms and one giving nitric oxide and oxygen radical anions.…”

Dissolution of UO2 by Photochemical Reaction

“…From this result we can confirm that 254 nm of wavelength emitted from the Hg-lamps may excite nitrate ions. In this regard, similar results have been described elsewhere[6,[10][11][12]. Thus, the rapid dissolution of U0 2 in the presence of…”

Influence of light on phenol compound reactivity in the presence of nitrates in abiotic solution

“…Dans le processus de photolyse des nitrates, les nitrites ne sont pas les seules espèces produites. La présence de radicaux OH* et NO2* a été démontrée par analyse spectroscopique (21). Des travaux plus récents ont montré que la production de radicaux OH' dans les eaux de surface était principalement provoquée par une photolyse lente des ions nitrates (23)(24).…”