Quenching Of Singlet Oxygen By Dissolved Organic Matter In Ice Phase

Dissolved organic matter（Dissolved organic matters,DOM）is a highly heterogeneous mixture,which plays an important role in the process of ecosystem.At the same time,DOM is also the main removal species and limiting factor for wastewater recovery and reuse.At present,researchers have studied various treatment technologies for removing DOM from wastewater（such as membrane separation technology,ion exchange resin,adsorption,etc.）.However,with the development of environmental chemistry,in recent decades,nuclear magnetic resonance,mass spectrometry,infrared spectroscopy and PARAFAC have been used to analyze the composition and structure of DOM.In the natural environment,DOM is an important component of ice and snow,and the photochemical reaction in snow and ice will significantly affect the chemical properties and composition of the atmosphere.For example,snowdrift may be the source of NOx and HNO2,as well as H₂O₂,CO and a series of volatile organic compounds（VOCs）,including formaldehyde and other carbonyl compounds.The photochemical reaction of snow and ice will also change its composition.Therefore,photosensitization reaction plays an important role in the study of the transformation of pollutants in snow and ice and the formation of photoactive species.However,freezing and thawing will change the properties of liquid water,so the general research methods of aquatic systems cannot be simply applied to the field of ice phase research.Singlet oxygen（¹O₂）is an oxidation species with unpaired electrons that is formed when atomic oxygen or oxygen molecules lose electrons.It can be produced in the atmosphere,organisms and industrial activities,and participates in a variety of chemical reactions.¹O₂ is a highly reactive species of free radicals that can react with other molecules,including organic molecules,iron ions,H₂O₂,etc.These reactions may lead to the degradation of organic compounds,the generation of new organic compounds,catalytic oxidation reactions,etc.In the process of pollutant degradation,¹O₂ can degrade some pollutants such as organic matter and gas pollutants into more stable substances through photolysis or chemical reaction.The DOM samples used in this experiment were all purchased from the International Humic Acid Association,namely Suwannee River fulvic acid（SRFA）and Leonardite humic acid（LHA）.In this study,furfuryl alcohol（FFA）was selected as the molecular probe of single oxygen（Single oxygen,¹O₂）,and the indoor simulation of photodegradation was used to determine the photosensitization ability of DOM generation and quenching of ¹O₂ in the ice phase.Normally,λ>290 nm light source can simulate sunlight,so this experiment uses a 500 W mercury lamp to add 400 nm to simulate sunlight to carry out indoor simulated photodegradation experiment.The structure and chemical properties of DOM were characterized by spectroscopy characteristic parameters;Quantitative analysis of ice phase DOM photogeneration and quenching of ¹O₂ from different sources,concentrations,and p H;The relationship between the steady state concentration of DOM and the quenching constant of ¹O₂ in the ice phase and the characteristic parameters of spectroscopy was compared and analyzed.The results show that the spectroscopy performance parameters of frozen DOM will change;The degree of quenching of ¹O₂ by DOM in the ice phase decreases with increasing concentration;Under alkaline conditions in the ice phase（p H=9）,the difference in quenching effect between the two types of DOM on ¹O₂ is the greatest.There is a significant positive correlation（p<0.05）between the steady-state concentration of ¹O₂([¹O₂]_SS,DOM)produced by DOM with different concentrations in the ice phase and the spectroscopy characteristic parameters a₂₅₄,a₃₀₀ and fluorescence intensity of[¹O₂]_SS,DOM produced by DOM with different p H in ice phase,and there is no correlation between DOM and DOM’s spectroscopy characteristic parameters a₂₅₄,a₃₀₀ and fluorescence intensity（p>0.05）;There is no correlation between the quenching constants(k_q,DOM)of DOM to ¹O₂ at different concentrations in the ice phase and the spectroscopy characteristic parameters a₂₅₄,a₃₀₀ and fluorescence intensity of DOM（p>0.05）;There is no correlation between k_q,DOM,spectroscopy characteristic parameters a₂₅₄,a₃₀₀ and fluorescence intensity under different p H conditions in the ice phase（p>0.05）.