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

摘要

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 × 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 and N3~· radicals were found to react with 4-NP with rate constants of 4.1 × 10~9 dm~3 mol~(-1) s~(-1) and 2.8 × 10~8dm~3 mol~(-1) s~(-1), respectively. Differences in the absorption spectra of species formed in the reactions of 4-NP with ~·OH and N3~· radicals suggested that ~·OH radicals add to the aromatic ring of 4-NP along with electron transfer reaction, whereas N3~· radicals undergo only electron transfer reaction. At pH 9.2, rate constants for the reaction of ~·OH 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.