Photochemical Production Of Singlet Oxygen From Black Carbon In Ice

Black carbon is widely distributed in ice and snow,but there is no research about the photochemical reaction of black carbon in ice.Black carbon in ice may singlet oxygen?¹O₂^*?produce free radicals by photochemical reaction and have an important effect on the migration and transformation of pollutants in ice.In this paper,6 types of black carbon or black carbon like materials,which are candle soot,coal power plant fly ash,ponderosa pine biocahr,graphite,carbon nanotube tubes and carbon black,are studied by using Xenon lamp?Xe?as the light source.The photochemical effects of ice are measured by the concentration of ¹O₂^* and the photon flux is normalized by coefficients.At the same time,according to the experimental results,some calculations are carried out,and the concentration of ¹O₂^* from black carbon in nature is estimated,and whether it is an important sink for some contaminants is evaluated.In addition,an experiment separates the various components?large particles,small particles,organic matter and inorganic matter?in the black carbon,in order to find which are the active components involved in the formation of ¹O₂^*.Finally,several typical factors affecting this reaction,like media states?ice or water?,black carbon concentration and temperature,are examined.The main conclusions are as follows:1 The physical properties of black carbonIn 6 types of black carbon or black carbon like materials,only carbon nanotube diameter is nanometer?nm?level,the rest are micron??m?level.The specific surface area of black carbon with large particle size is small.The absorbance of same mass concentration of black carbon from high to low: carbon black> candle soot> carbon nanotubes> graphite> pine biochar> power plant fly ash.For the black carbon filtrate after filtration?ie removal of diameter larger than 0.22?m component?,the absorbance of the carbon nanotube is significantly higher than others.In the other 5 types of black carbon filtrate,the order of absorbance from high to low is biochar> candle soot> power plant fly ash> graphite> carbon black.After filtering,black carbon filtrate still absorbs light that means there should be still a small particle size black carbon or other substances in black carbons.The absorbance of carbon nanotubes filtrate is significantly higher than other black carbon may be due to the smaller average particle size,and part of particle is still present in the filtrate.2 Production of ¹O₂^*from black carbonAfter the Xenon lamp irradiation,the 4 types of black carbon,candle soot,biochar,carbon nanotubes and graphite,consume Furfural alcohol?FFA?,which means the formation of ¹O₂^*.Carbon black and power plant fly ash are almost not consuming FFA.Different types of black carbon produce have different ¹O₂^* concentration?already normalized by photon flux,the same below?.The order from high to low is carbon nanotubes> candle soot> biochar> graphite.If remove the large particles?particle size>0.22?m?in black carbon suspension and then freeze and illuminate the filtrate,different results are acquired.The formation of ¹O₂^* from high to low order: graphite> candle soot> biochar> carbon nanotubes.This difference may be due to the large particles of black carbon in the process of freezing maybe adsorb small particles and other components,affecting the mass transfer of these components in the ice,resulting in a lower ¹O₂^* production.3 Impact of pollutantsBy calculation,the ¹O₂^* concentration from balck carbon is 1.6 11E-13 M in nature.If it is assumed that this concentration is ¹O₂^* concentration in natural ice and snow environment.The ¹O₂^* in ice may be an important sink for these pollutants such as aniline,naphthalene,quinoline,histidine and tryptophan.4 The functional components of the reactionRemove the small particles?<0.22?m?and the organic components in candle soot and graphite,leaving only the large particles and the inorganic components,and use this treated black carbon for freezing and illuminating.It is found that the that 2 black carbons don't produce ¹O₂^*,which indicate that the large particles?> 0.22?m?and inorganic matter don't participate in the formation of ¹O₂^* by photo reaction.Remove part of the organic matter in the carbon nanotubes and graphite,retaine the other components,and used this treated black cabon for freezing and illuminating.It is found that there is a difference of ¹O₂^* formation between the original components and treated black cabon which is removal of the organic matter,and indicating that for the graphite,the organic matter is involved in the photoreaction and producing ¹O₂^*.Carbon nanotubes don't come to an effective conclusion.5 Influencing factors of ¹O₂^* formationCompare the reaction of candle soot and biochar in ice and in water,it is find that the freezing concentration effect significantly promote the reaction,and the ratio is 10³ to 10⁴,which is in the regular range 10² to 10⁵.Compare the formation of ¹O₂^* in different concentrations of black carbon?1,10,100 mg/L?in ice.All of black carbon?carbon nanotubes,candle soot,biochar,graphite?meets the 10 times relations.Compare the formation of ¹O₂^* in different temperatures?-10? and-5??.The differences of ¹O₂^* formed by black carbon are not obvious.