Photochemistry of the aqueous nitrate system. I. Excitation in the 300-m.mu. band

Abstract

Nitrate solutions have been photolyzed in the first weak band at 300 mp using the filtered output of a 450-W high-pressure mercury lamp. In neutral solution, nitrite formation is initially nonlinear with time, falling off to a low constant rate. This behavior has been investigated as a function of nitrate concentration, nitrite buildup, and addition of nitrite prior to photolysis, The results are quantitatively consistent with process A NO3--% NO2-+ 0 0 + Nos--% 0 2 + Not-and allow evaluation of kz/kl as -2 X lo4; 9 (NOP-)A 'v 4 X independent of intensity and nitrate concentration. Addition of radical scavengers (As(III), ethanol, H20z, and benzene) prior to photolysis causes drastic increase in rate of nitrite formation. Consideration of reaction stoichiometrics and mechanisms leads to the conclusion that the additives are scavenging OH radicals. The scavenging kinetics are described by the Jortner-Ottolenghi-Stein (JOS) equation, from which the scavenging rate constant ratios HzOz:EtOH:As(III) are derived and found to be the same as the OH radical rate constants. Accordingly, it is suggested that a second primary process, B, takes place.Nos-pH has a pronounced effect on the photolysis. Nitrite formation becomes linear with time and increases severalfold. Two regions of rapid change may be distinguished: J (1) pH 8-10; (2) pH 11-13. The behavior a t pH 8-10 may be accounted for by changes in process A. From pH 11 to 13, the change may be correlated with ionization of OH radical (pK = 11.9) formed in process B. At the plateau pH 10.3, a dependence of @(NO2-) on nitrate concentration is found, which can be described by a JOS treatment. IntroductionIn the ultraviolet region, aqueous solutions of nitrate show two distinct absorption bands, a weak one centered at -300 mp (e 7.1 at 304 mp @ I 25", f = 1.4 X and an intense band in the far-ultraviolet region

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

“…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.…”

“…The photoreduction of nitrate in aqueous solution was reported as early as 1907 by Thiele [2]. Without catalyst, the toxic nitrite seems to be the major product, although the literature is not entirely consistent with regard to the product distribution and a possible nitrate/nitrite equilibrium [3][4][5][6][7].…”

Development and Intercalibration of Ultraviolet Solar Actinometers

“…In this paper, we introduce two broadband sunlight actinometers that are based on the photolysis of nitrate (29)(30)(31)(32)(33)(34) and nitrite (32,(35)(36)(37). The primary reactive intermediate of nitrate and nitrite photolysis, the hydroxyl radical, reacts with benzoic acid leading to the formation of monohydroxybenzoic acids (38), including SA or pHBA (39).…”

On the photolytic separation of halogens from sea water concentrates

“…The NO~ oxidizer is also formed at much blander conditions (about 10-50 Torr and room temperature) from NO or NzO3 and oxygen (Guillory andJohnston, 1963, 1965). This transient may, in turn, be expected to yield highly oxidizing OH" or O ~ radicals during its decomposition in solution (Martin et al, 1964) which, in turn, could react with NO~ yielding again NO~ (Daniels et al, 1968;Daniels and Wigg, 1969). It has also been shown that radiolysis of nitrates in aqueous solution yields those radicals (Hyder, 1965;Daniels, 1966) whereby subsequent formation of NO 2 may be expected in those aqueous systems.…”