Effects Of Different Conditions On The Photogeneration Of Singlet Oxygen By Dissolved Organic Matter In Water

In recent years,global warming and other serious environmental problems are becoming increasingly serious.Global warming has caused a series of extreme climate events around the world,including high-temperature heat waves,low-temperature chilling damage,floods and droughts.In addition,global warming has caused rising temperatures in the North and South Arctic,causing glaciers to melt,and rising sea levels,which may flood coastal areas and the cities.It can also cause a series of nasty reactions.The ocean serves as one of the largest dissolved organic carbon(DOC)dynamic reservoirs on the planet.If one percent of the dissolved organic carbon in the ocean is oxidized,a large amount of carbon dioxide will be generated.Carbon dioxide as one of the gases that affect the global greenhouse effect,will directly cause a devastating blow to the global ecological environment and climate change.Therefore,dissolved organic matter(DOM)has a significant impact on the regulation and regulation of global climate change and the global carbon cycle and ecological environment.The DOM samples used in this experiment were purchased from the International Humus Association.The water source DOM: Suwannee River NOM(RO isolation)(SRNOM,2R101N),Upper Mississippi River NOM(RO / ED isolation)(UMRNOM,1R110N);terrestrial DOM: Elliott Soil Humic Acid Standard V(ESHA,5S102H),Leonardite Humic Acid Standard(LHA,1S104H).In this study,furfuryl alcohol was selected as the molecular probe,and the photosensitization ability of DOM in the aqueous phase to produce singlet oxygen was studied by using indoor simulated photolysis.In general,a light source with ?> 290 nm can simulate sunlight,so a 500 W xenon lamp built in a photochemical reactor is used to simulate sunlight.And by characterizing its ultraviolet-visible spectrum and three-dimensional fluorescence spectrum,exploring the differences in the composition and chemical properties of DOM,the relevant conclusions about the effects of different conditions on the photoinduced formation of singlet oxygen by dissolved organic matter in the water phase are as follows:The steady-state concentration of 1O2 in 4 different DOM solutions was calculated through photochemical experiments.The steady-state concentration of 1O2 was between 0.44 and 1.50 × 10-14 M.It was found that the strong photosensitizing ability of terrestrial DOM to produce 1O2 may be related to the higher proportion of aromatic ketones and quinones in the structure.For the two water sources DOM,the greater the concentration of DOM,the stronger the absorbance and fluorescence intensity,and the stronger the photosensitizing ability to produce 1O2.According to the analysis of ultraviolet spectrum,the larger E2 / E3 is,the faster the rate of 1O2 is generated.The generation of 1O2 has no charge transfer and only energy transfer.Under acidic conditions,water-source DOM molecules make the molecular structure larger because of intermolecular interactions,and it is difficult for 1O2 to diffuse outward from the inside of the DOM molecules,which affects the ability of DOM to produce 1O2.When the p H is increased,the aqueous solution is under alkaline conditions,and the molecular structure is relatively loose,the yield of excited DOM is increased,and the ability of DOM to produce 1O2 is also enhanced.Water-borne DOM generally has a higher fluorescence index(FI),freshness index(? / ?),and a lower humus index(HIX),which can indicate that the source of water-borne DOM components is mainly algae or microorganisms in water Metabolites(such as amino acids)and less humus.Terrestrial DOM generally has a lower fluorescence index(FI),freshness index(? / ?),and a higher humus index(HIX),which can indicate that the source of terrestrial DOM components is mainly terrestrial humus substances.And forests have a large amount of lignin in vegetation,and the content of humus is large.In addition to the influence of natural conditions,the disturbance of human activities is also the main reason for the difference of DOM from different sources.Under aqueous conditions,the apparent rate constants of furfuryl alcohol and DOM solution were significantly positively correlated with SS350-400 and HIX(P <0.05).During the photolysis of DOM from different sources in the water phase,the molecular weight,total organic carbon content,and aromatic degree of DOM are the same.The more fat content of DOM and the greater the degree of humification,the stronger the photosensitivity of DOM.The results of this study indicate that factors such as the formation environment,concentration,and p H of dissolved organic matter have different effects on their photogenerated 1O2.