Employing experiment and density functional theory calculation to unveil the effects of light-absorbing media on photodegradation of polycyclic aromatic hydrocarbons

Photodegradation kinetics of polycyclic aromatic hydrocarbons(PAHs) strongly depends on the effects of light-absorbing constituents of the environmental media.In order to unveil the effects of the light-absorbing constituents on the photodegradation of PAHs,three solvents(methanol,acetone and dimethylsulfoxide) were selected to model the light-absorbing constituents of environmental media,and were employed in a simulated photodegradation experiment for three PAHs(phenanthrene,pyrene and benzo[a]pyrene).Among the three solvents,methanol has very weak sunlight absorbance,while acetone and dimethylsulfoxide(DMSO) have strong sunlight absorbance.The photoinduced electron / energy transfer reactions between the solvents and PAHs were analyzed with the aid of density functional theory(DFT) calculation.The results indicated that acetone significantly inhibited the photodegradation rate of phenanthrene and pyrene,but enhanced the photodegradation of benzo[a]pyrene.DMSO significantly inhibited the photodegradation rate of phenanthrene,but enhanced the photodegradation of pyrene and benzo[a]pyrene.After filtering out the light-absorption of DMSO,the photodegradation rate constants of the three PAHs in DMSO were similar to those in methanol.The computational results indicated that the electron transfer from PAHs to the excited state acetone(or DMSO) is the main reason which influenced the PAHs photodegradation.