A fluorescence quenching study of PAH compounds in aqueous solutions containing interacting cosolutes
The apparent solubilities of perylene, benzo(e)pyrene and pyrene in water in the presence of either sodium benzoate, phenol, sodium alginate, or sodium dodecylsulfate were determined. The three polynuclear aromatic hydrocarbons (PAHs) were selected as representative hydrophobic organic compounds (HOCs). The solubility enhancements were measured as a function of cosolute concentration. The results revealed that the solubilities of the PAHs are significantly enhanced in water in the presence of each cosolute. These solubility enhancements were investigated with fluorescence quenching methods. A negatively charged quencher and a neutral quencher, iodide and nitromethane respectively, were used to examine the microenvironment of the dissolved PAH molecules in these multicomponent aqueous systems. The solubility enhancements and the fluorescence quenching results of the PAHs by benzoate were successfully modeled by means of a complexation model. Benzoate showed very similar orders in complexation with every PAH tested and the order did not vary depending on its concentration, whereas phenol showed higher order with more hydrophobic PAH. The driving forces for association (solvation) are believed to be non-specific forces (van der Waals forces) between PAH and cosolute molecules. SDS monomers also enhanced the solubility of PAHs through complexation below the cmc. In the fluorescence quenching study, pyrene proved to be a good probe for measuring the cmc values of DS against varying ionic strength. A macromolecule, alginate, enhanced the solubility of PAHs in water, and fluorescence studies indicated that PAH molecules associated with alginate are hardly fluorescing, implying alginate behaves like some humic acids which can associate with PAHs and quench their fluorescences by absorbing energy from the excited electrons. ^
Major Professor: Chad T. Jafvert, Purdue University.
Engineering, Sanitary and Municipal|Environmental Sciences