Oxidative Degradation of Triazine Derivatives in Aqueous Medium:  A Radiation and Photochemical Study

Abstract

Pulse and steady state radiolysis techniques have been used to determine the bimolecular rate constants and to investigate the spectral nature of the intermediates and the degradation induced by hydroxyl radicals ((*)OH) with 1,3,5-triazine (T), 2,4, 6-trimethoxy-1,3,5-triazine (TMT), and 2,4-dioxohexahydro-1,3, 5-triazine (DHT) in aqueous medium. A competitive kinetic method with KSCN as the (*)OH scavenger was used to determine the rate constants for the reaction of (*)OH with T, TMT, and DHT. The bimolecular rate constants are 3.4 x 10(9), 2.06 x 10(8), and 1.61 x 10(9) dm(3) mol(-)(1) s(-)(1) respectively, for T, TMT, and DHT at pH approximately 6. The transient absorption spectra obtained from the reaction of (*)OH with T, TMT, and DHT have single absorption maxima at 320, 300, and 300 nm, respectively, and were found to undergo a second-order decay. The formation of TOH(*) [C(6)OH-N(5)-yl radical], TMTOH(*) [N(5)OH-C(6)-yl radical], and DHT(*) [C(6)-yl radical] is proposed from the initial attack of (*)OH with T, TMT, and DHT, respectively. A complete degradation of TMT (10(-3) mol dm(-3)) was obtained after absorbed doses of 5 kGy in N(2)O-saturated solutions and 16 kGy in aerated solutions. A similar degradation pattern was obtained with DHT in N(2)O-saturated solutions. Complete degradation was observed with an absorbed dose of 7 kGy. On the basis of the results from both pulse and steady state radiolysis, a possible reaction mechanism involving (*)OH-mediated oxidative degradation is proposed. A complete photodecomposition of DHT was also observed in the presence of ferric perchlorate using ultraviolet light at low pH. Photoinduced electron transfer between Fe(III) and DHT in the Fe(III)-DHT complex and subsequent formation of DHT(*) are proposed to be the major processes that lead to the complete degradation of DHT at pH 3.

Fenton-enhanced γ-radiolysis of cyanuric acid

“…However, this linearity was observed only up to a concentration of Fe(II) as 10 −4 mol dm −3 above which this follows a saturation point (data not shown). Similar experiments were carried out using another triazine, DHT, which is known to have high reactivity with hydroxyl radical [16]. Radiolysis in the absence of Fe(II) showed a complete degradation after about 7000 Gy (Fig.…”

“…The pattern of reaction of • OH with a number of triazine derivatives is reasonably well documented [11,15,16]. • OH undergoes either addition or hydrogen abstraction reaction with atrazine [15,16]. It was also shown that the major end product of oxidation of atrazine by • OH is cyanuric acid (OOOT) [17].…”

“…Similar to other pollutants the conventional methods used for the decontamination of wastewater are not effective in the case of triazines and hence more work is being concentrated for the development of new technologies for their complete degradation. There are several reports on the degradation of triazine derivatives using different AOPs [10][11][12][13][14][15][16]. It is seen in all these reports that only a transformation of the atrazine to a relatively less toxic cyanuric acid can be achieved.…”

Impact of Lamp Choice and H2O2Dose on Photodegradation of Nitrobenzene

“…The k OH value can be directly measured using pulse radiolysis, but this method requires specialized equipment ( Joseph et al, 2000).…”

Oxidation of substituted triazines by sulfate radical anion (SO) in aqueous medium: a laser flash photolysis and steady state radiolysis study

“…In situ generation of OH by various methods such as photo-fenton reaction, 11 photolysis of ozone, 12 photolysis of hydrogen peroxide, 13 photochemical reactions of titanium dioxide, 14 radiolysis of water, 15 and sonochemical method 16 are the generally used AOPs. A considerable attempt has been made with AOPs based on ozone 17 and hydroxyl radicals [18][19][20] to investigate the complete degradation of triazines in the past. A number of reports demonstrated the high reactivity of OH with triazines (diffusion controlled) and have shown a degradation pathway in aqueous state.…”