Role of primary reaction initiated by 254 nm UV light in the degradation of p-nitrophenol attacked by hydroxyl radicals.
The degradation kinetics of p-nitrophenol (p-NP) exposed to 254/185 nm UV light were studied in two modes, i.e., 254 nm UV light intensity enhanced mode and normal mode. It was observed that the extra 254 nm UV light source accelerated the degradation process both in the presence and the absence of oxygen. Considering that hydroxyl radical (*OH) is the dominant factor that causes the degradation of p-NP, the enhanced degradation that occurred in the presence of the extra light source was attributed to the synergistic effect between *OH attack and the primary reactions initiated by 254 nm UV light. The synergistic effect has been confirmed by 266 nm laser flash photolysis (LFP) experiments. It is demonstrated that the phenoxy radical generated from the photoionization of p-NP is capable of reacting with *OH. On the basis of these results, it should be noted that UV light could cause more severe damage to p-NP attacked by *OH in aqueous solution.
Effects of uv light on dilute aqueous solutions of m- and p-nitrophenol
Circumstantial evidence derived from an exploratory study by different methods suggests that the effect of UV light on dilute aqueous solutions of m- and of p- nitrophenol is largely nitrite displacement by OH− nucleophile from the solvent, with formation of HNO2 in the initial stages. Dilute aqueous picric acid solutions behaved in a manner more or less similar to that of the mononitrophenols and also similar to that of its methanolic sodium methoxide solutions as has been reported in the literature. In all cases, when ultimately the aqueous solutions are decolourized, photofragmentation seems to ensue.
Kinetics and spectroscopy of the SO4− radical in aqueous solution
Abstract Laser flash photolysis of S2O82− at 248 nm and 266 nm has been employed in conjunction with time-resolved long path absorption detection to investigate the kinetics and spectroscopy of the SO4− radical in aqueous solution. Much lower radical concentrations were employed than in all previous time-resolved investigations of this well-studied radical, thus minimizing potential interferences from side reactions, ϵΦ, the product of the 443 nm SO4− extinction coefficient (ϵ) and the quantum yield for SO4− production from 266 nm photolysis of S2O82− (Φ), was measured under conditions where the optical path length was well known, and where the number of photolysis photons absored per cubic centimeter of solution was uniform throughout the detection region and accurately measured; we find that ϵΦ = 2770 ± 280 M−1 cm−1. The first quantitative measurement of a rate coefficient for the slow, endothermic reaction. was carried out; the result is k1 (298 K) = 360 ± 90 s−1. 298 K kinetic data are also reported for the reactions We find that k−1 = (3.5 ± 0.5) × 105 M−1 s−1 and that, in the zero ionic strength limit, 2k2/ϵ = (3.9 ± 1.1) × 105 cm s−1.