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.
Transient and steady-state photolysis of p-nitroaniline in aqueous solution.
Both transient photolysis and steady-state photo-degradation experiments were performed to gain insight into the kinetics and mechanisms of degradation of p-nitroaniline (p-NA) in aqueous solutions. Monophotonic photo-ionization of p-NA was characterized by 266 nm Laser Flash Photolysis (LFP). The quantum yield of e(aq)(-) was calculated. Radical cations and neutral radicals of p-NA were identified, respectively. The LFP of p-NA with H(2)O(2) in aqueous solutions was investigated for the first time. For steady-state photo-degradation, degradation of p-NA was observed at diverse irradiation conditions under 254 nm UV light. Direct photo-degradation of p-NA by 254 nm UV light in aqueous solution was very difficult. Once H(2)O(2) was added into the experimental system, degradation of p-NA was enhanced remarkably. In the absence of O(2), degradation rate increased rapidly along with the irradiation time and reached 80% at 10 min. p-NA could be totally removed after 15 min in UV/H(2)O(2) process. In the presence of O(2) and H(2)O(2), degradation rate increased linearly along with the irradiation time and reached 80% at 7.5 min. p-NA could be totally removed after 10 min. The mechanisms behind the photo-degradation of p-NA were discussed.
Activation Energies for Reactions of the Hydrated Electron
INFORMATION about the activation energies of reactions of the hydrated electron, e−aq, is important for the elucidation of its reaction mechanisms and of the process of transfer of e−aq in water.