Comparative Study On Photochemical Behavior Of Nitro-Polycyclic Aromatic Hydrocarbons/Hydroxy-Naphthalene Congeners In Water And In Ice

Nitro polycyclic aromatic hydrocarbons（nitro-PAHs）are a kind of emerging pollutants widely detceted in the environment,as well as appear carcinogenicity,mutagenicity and teratogenicity.These pollutants belong to high-risk pollutants because of their similar structures with polycyclic aromatic hydrocarbons（PAHs）.It is a new type of pollutant with potential hazards.Hydroxynaphthalene congeners（OH-Naps）compounds are widely used in the synthesis and production of pesticides and dyes,which are continuously detected in the natural environment and are extensively concerned.In the surface water,photochemical degradation is the main way to reduce these two types of pollutants.Therefore,this paper selects three nitro-PAHs and four OH-Naps as the research objects to study the differences of their photolysis kinetics in the water phase and the ice phase,focusing on their sensitized photolysis mechanism,photolysis products,reaction paths and toxic effects,and revealing the effects and rules of different dissociation forms of OH-Naps on photolysis.The photochemical behavior of 1-nitropyrene（1-Npyr）,2-nitrofluorene（2-Nflu）and 9-nitrophenanthrene（9-Nphe）in water and in ice were compared,including photodegradation kinetics,the contribution rate of·OH and ¹O₂ in self-sensitized photolysis,transformation products of direct photolysis and toxicity evolution trend.The photolysis of nitro-PAHs follows the first-order reaction kinetics in the simulated sunlight irradiation（λ>290 nm）,and the range of quantum yield（Φs）of nitro-PAHs in water and ice was 2.20× 10^-5（2-Nflu）～2.23× 10^-4（9-Nphe）and 1.99× 10^-5（2-Nflu）～3.52× 10^-4（1-Npyr）.The results of reactive oxygen species quenching experiments showed that the contribution rate of OH and ¹O₂ in water to photodegradation was higher than that in ice.This is because the physical properties of ice reduce the light quantum flux and weaken the reactivity of the compounds.A total of 6 products in water and ice were obtained by Agilent 6470 HPLC-MS/MS,which showed different reaction paths.The most important products were ketones,anthraquinones and hydroxylation products.According to the toxicity test and SPSS analysis,1-Npyr and 2-Nflu showed photo-modified toxicity to Vibrio fischeri.Then the photochemical degradation rates of 1-naphthol（1-OHN）,2naphthol（2-OHN）,4-chloro-1-naphthol（4-Cl-1-OHN）,4-nitro-1-naphthol（4-NO₂-1-OHN）in different phases were studied.The results showed that 2-OHN had the highest degradation rate in the water phase,followed by 4-Cl-1-OHN,1-OHN,4-NO₂-1-OHN,and the photolysis rate of 4-Cl-1-OHN was the fastest in the ice phase.Since the hydroxyl（-OH）on the 2-OHN has higher reactivity than-OH on the 1-OHN,the substitution of chlorine on the benzene ring of naphthol can promote photolysis compared to nitro substitution.Then the effect of OH on the photodegradation of OH-Naps were investigated,and it was found that the four substances showed high oxidation activity with OH.The bimolecular reaction rate constant（k·OH）in water ranged from 2.4× 10¹⁰～12.82× 10¹⁰ L/（mol·s）,and the k·OH in ice ranged from 1.68× 10¹⁰～7.87× 10¹⁰ L/（mol·s）.By estimating the half-lives of OH-Naps photochemical degradation in surface water and snow surface,it can be seen that the reduction of 1-OHN,2-OHN and 4-Cl-1-OHN was mainly direct photolysis,and the main reduction of 4-NO₂-1-OHN was indirect photolysis with free radical reaction.In order to further reveal the differences and similarities of photodegradation kinetics of OH-Naps in natural water and snow environment,the effects of different pH on their photodegradation were investigated,it was found that in the aqueous phase,the photodegradation rate of the four substances showed a positive correlation with the increase of pH,and the quantum yield also showed the same trend.The photolysis rate of 4-NO₂-1-OHN in ice was the fastest at pH 6,and the decrease and increase of pH inhibited its photolysis.The photolysis products of 4-Cl-1-OHN and 4-NO₂-1-OHN were indentified by HPLC-MS/MS,a total of 6 products were detected,and the main photolysis products were 1,4-dinaphthoquinone and 2-hydroxy-1,4-dinaphthoquinone,the photochemical reactions involved are photodechlorination,nitro removal,photooxidation,photoisomerization,hydroxylation and multiple hydroxylation.It was found that the main photolysis paths of both were the formation of carbon-oxygen double bonds after photo-dehydrogenation,or the formation of 1,4-dinaphthoquinone and 2-hydroxy-1,4-dinaphthoquinone by photooxidation and hydroxylation.To sum up,this thesis reveals the differences in photochemical behavior of three nitro-PAHs and four OH-Naps in water and ice.Both of these substances can undergo direct photolysis or indirect photolysis with OH.Nitro-PAHs can undergo self-sensitized photolysis.The specific mechanism of action and photolysis in the two phases were different.OH-Naps can undergo photooxidation reaction with OH and achieve high degradation rate in a short time.The above results are of great significance for revealing the photochemical behavior of new pollutants such as polycyclic aromatic hydrocarbon derivatives in water and ice media.