The Laser Flash Photolysis And UV Photolytical Degradation Of Two Kinds Of Phenolic Pollutants

With the rapid development of chemical industries such as petroleum chemicalengineering, plastics,synthetic fabric, coking and so on, more and more phenoliccompound wastewater was discharged into our environment. Phenolic organic compoundis a kind of recalcitrant compounds, which is toxic to plants, animals, and human even atlow concentration. So the investigation of high efficient treatment technology to treatphenol waste water is of great significance.In this paper,4-n-NP and p-NP were chosen as the model compound. The photolyticalbehavior of4-n-NP in ethanol、acetonitrile and acetonitrile/water solution was investigatedby use of266nm laser flash photolysis and254nm photolysis. And the effect of variousphysical&chemical conditions on the degradation of4-n-NP was explored, meanwhile O₃involved in the reaction of p-NP attacked by·OH radical was also investigated.The main results were as follows：Laser flash photolysis experiments showed that4-n-NP can be either photoionized orphotoexcited by266nm laser. The characteristic transient absorption spectra of radicalcation formed from photoionization and excited triplet formed from photoexcitation of4-n-NP were obtained. The reaction rate constant of2.71×10⁸dm³·mol^-1·s^-1was calculatedfor the self-quenching of34-n-NP*. It has also confirmed that4-n-NP can be oxidized bySO₄^.-, which produced from photo-decomposition of S₂O₈^2-exposed to266nm laser, toproduce radical cation4-n-NP+and the rate constant for reaction of SO₄^.-and4-n-NP isdetermined to be2.85×109dm³·mol^-1·s^-1. The radical cation4-n-NP+will be transferredinto its neutral radical4-n-NP via deprotonation over pH2.2.254nm UV light is proved to be able to decompose4-n-NP directly slowly. It can bedegraded completely in120mineutes. Once H₂O₂was added into the experimental system,degradation of4-n-NP was enhanced remarkably. In the presence of O2and H₂O₂, removalrate increased linearly with increment of the irradiation time and reached80%at15min.4-n-NP could be totally removed after30min. Accordingly, with addition of K₂S₂O₈thedegraded efficiency of4-n-NP reached the highest and it can be degraded completely in3.5minutes.254nm UV degradation of p-NP was very loe and removal rate was less than15%after5hours exposure to UV light. Once H₂O₂or O₃was added into the experimentalsystem, p-NP can be degraded completely in40minutes and75minutes, respectively. Thedegraded efficiency of p-NP attacked by·OH was compared with that in the presence and the absence of O₃. It can be suggested that O₃has some synergic effect in the reactionbetween p-NP and·OH, and may enhance the degradation of p-NP.