Study On Photochemical Degradation Of Two Kinds Surfactants Of In Seawater

Marine organic photochemistry (MOP), as one of the important branches of marine chemistry, has a close relationship with many marine subjects such as marine biology and marine environmental science. The comprehensive study on MOP is of realistic significance for further understanding the removal patterns of organic pollutants in ocean.The photodegradation of surfactants is an important pathway for their decomposition and transformation in natural environment. Surfactants molecules can absorb the light energy and be photodegraded themselves (direct degradation).The degradation may also be sensitized by another compound (or other compound), which is referred to as indirect degradation. It is of great significance to study the photodegradation of surfactants in seawater, because through the study, we can get the products and pathway for their photodegradation in natural environment and realize the safty of surfactants in order to instruct the use of surfactants and synthesize of new products.Based on the research work, the thesis focused on the photochemical degradation reaction of two representative surfactants in seawater by the simulated method in laboratory. Upon the instrument determination and analysis, we systematically studied the photochemical degradation of sodium dodecylbenzene sulfonate(SDBS)and Tween80 and obtained the following results:1. Photochemical degradation of sodium dodecylbenzene sulfonate(SDBS)(1)SDBS could be degraded remarkably under the irradiation of 300 W high pressure mercury lamp and showed the first-order reaction kinetic behavior. Under the different experimental conditions,the rate constants (k) of SDBS varied from 0.0169 to 0.0289 min-1. (2)Many factors in the experiments would influence the photodegradation:a.Light source: SDBS was photodegraded a little under the irradiation of sunlight while it could be significantly degraded under the irradiation of high pressure mercury lamp.The photolysis rate of SDBS was faster under 500W high pressure mercury lamp than under 300W high pressure mercury lamp because the photodegradation of the SDBS was greatly influenced by light intensity.b.Aquatic media: The photodegradation of SDBS in deionized water was fastest. Compared with seawater, synthetic seawater exhibited somewhat faster photo-reaction rate for SDBS.c.Heavy metal ions: In all the reactions, different ions in different reaction systems displayed different roles. The results were obtained by changing the concentration of five heavy metal ions in SDBS solution. The effects of heavy metal ions were resulted mainly from the interaction between ions and aquatic media.d.Photosensitizer: The selected photosensitizer acetone and humic acids could accelerate the reactions of SDBS and the degree of effect was determined by reactant and aquatic media.(3)pH: The pH of solutions reduced in deionized water when pH was measured in the process of photodegradation of SDBS, but it tended to unchanged in natural seawater and synthetic seawater.2. Photochemical degradation of Tween80(1)Tween80 was degraded under the irradiation of 500 W high pressure mercury lamp within two hours. Under the different experimental conditions, the photolysis of Tween80 showed the first-order reaction kinetic behavior and the rate constants (k) of Tween80 varied from 0.0046 to 0.0183 min-1.(2)Many factors in the experiments would influence the photodegradation:a.Aquatic media: The reaction in seawater was slowest while it seemed a bit faster in synthetic seawater than that in deionized water.b.Heavy metal ions: In three different aquatic medias, four metal ions such as Cu2+, Zn2+, Cd2+, Pb2+ displayed different roles.c.Photosensitizer: The selected photosensitizer acetone could accelerate the reactions of Tween80 and the degree of effect was determined by reactant and aquatic media.In brief, for the two toxic pollutants in seawater, a series of results have been obtained in the respects of photochemical degradation, photocatalytic degradation, kinetic behavior and the factors influencing them. Based on the experimental results in this thesis, we can have a further understanding of the photodegradation situations of these two kinds of surfactants in the marine environment.