Radiolytic degradation of 4-nitrophenol in aqueous solutions: Pulse and steady state radiolysis study

The radiation induced degradation of 4-nitrophenol (4-NP) has been studied by gamma irradiation, while the reactivity and spectral features of the short lived transients formed by reaction with primary transient radicals at different pHs has been investigated by pulse radiolysis technique. In steady state radiolysis a dose of 4.4 k Gy is able to degrade 98% of 1 x 10(-4) mol dm(-3) 4-NP. 4-NP has pK(a) at 7.1, above which it is present in the anionic form. At pH 5.2, (OH)-O-center dot and N-3(center dot) radicals were found to react with 4-NP with rate constants of 4.1 x 10(9) dm(3) mol(-1) s(-1) and 2.8 x 10(8) dm(3) mol(-1)s(-1), respectively. Differences in the absorption spectra of species formed in the reactions of 4-NP with (OH)-O-center dot and N-3(center dot) radicals suggested that (OH)-O-center dot radicals add to the aromatic ring of 4-NP along with electron transfer reaction, whereas N-3(center dot) radicals undergo only electron transfer reaction. At pH 9.2, rate constants for the reaction of (OH)-O-center dot radicals with 4-NP was found to be higher by a factor of 2 compared to that at pH 5.2. This has been assigned to the deprotonation of 4-NP at pH 9.2. (C) 2013 Elsevier Ltd. All rights reserved.