The Mechanism Of UV Photolysis Of Bromophenol And Its Coupling Activation Of Hydroxylamine

Bromophenols（BrPs）,common organic compounds,are widely used in the chemical synthesis of brominated flame retardants（BFRs）,herbicides,and antifungals.In addition,BrPs can be also generated from UV photolysis,thermal treatment,and biodegradation of BFRs.The emission of BrPs poses a potential threat to mammalian and human health due to its toxicity and endocrine disrupting activity.Photolysis is an important transformation method of organic pollutants in the natural environment.Therefore,it is necessary to study and clarify the transformation process and mechanism of BrPs in the natural water environment.Additionally,hydroxylamine（HA）and its derivatives are widely present in natural water environments as intermediate products of nitrogen fixation,nitrification and denitrification reactions,and one of the products of biodegradation of nitrogen-containing compounds.The presence of HA may affect the photolysis of BrPs;However,studies focusing on this process are currently lacking.Therefore,in this paper,the photolysis process of BrPs was firstly studied,and the photolysis process was completely revealed.On the basis,the influence of the presence of HA on the photolysis process of BrPs was investigated.The reaction mechanism of HA activation to generate hydroxyl radicals and reactive nitrogen radicals and the transformation pathway of bromophenol in the presence of HA were clarified.The main research contents are as follows:（1）Study on the UV photolysis process and mechanism of BrPs.First,the effects of pH and BrPs concentration on the photolysis and debromination of BrPs were investigated,with 2,4,6-tribromophenol（TBP）as a model pollutant.It was found that the photolysis rate of TBP depended on its molar absorption coefficient.Electron spin resonance（ESR）spectroscopy was used to identify the active species generated during the photolysis of BrPs in detail.The results indicated that the photolysis of TBP can generate carbon-centered radicals（C·）,hydrogen radicals（H·）,and hydrated electrons(e_aq^-).The roles of these reactive species in the photolysis and debromination of BrPs were quantitatively assessed by radical quenching experiments.It was demonstrated that photolysis and e_aq^-had main contribution in the photolysis and bromination of bromophenols.At pH₀ 4-11,the contribution rate of e_aq^- in TBP degradation reached 35.8%-40%.The TBP photolysis products were analyzed by liquid chromatography-mass spectrometry（LC-MS）,and a possible photolysis and debromination mechanism of TBP was proposed.UV photolysis of TBP exhibited good resistance to dissolved oxygen,Cl^-and HCO₃^-,and showed high performance for degradation and debromination of TBP in lake water samples.（2）Activation of HA during the photolysis of BrPs and its effect on the transformation of BrPs.Under anaerobic conditions,the effect of HA on the photolysis of BrPs was studied,and it was found that the presence of HA not only changed the production of active species,but also changed the degradation pathway of BrPs.ESR,probe experiments and quenching tests indicated that C·,H·,and e_aq^-were generated in the UV/TBP system,while·OH and reactive nitrogen radicals（·NH₂ and·NO₂）were additionally generated after the addition of HA.LC-MS analysis revealed that the presence of HA inhibited the accumulation of monohydroxy products by promoting its further transformation and debromination.The generation of reactive nitrogen radicals led to the formation of nitration and amination products.In the UV/TBP system,the conversion products of HA included both oxidation products such as N₂O and NO₂^-,and reduction products such as NH₄⁺.Among them,NH₄⁺accounted for 20.3%of the products,indicating that HA underwent a reduction reaction in the UV/TBP system.In addition,the activation of several HA derivatives and·OH generation in the UV/TBP system were also investigated.It was found that N-O bond cleavage in hydroxylamines was the main pathway of their activation.Accordingly,the activation mechanism of HA and its derivatives in UV/TBP system was proposed.Finally,it was explored that the presence of HA can also effectively promote the debromination and degradation of BrPs in actual wastewater,but at the same time it can also lead to the formation of nitrobromophenols with high toxicity and high environmental risk,which should attract extensive attention.