Excited States and Intermediate Species of Benzo[e]pyrene Photolyzed in Solution and Adsorbed on Surfaces

Abstract

Benzo[e]pyrene (BeP) is a widespread polycyclic aromatic hydrocarbon found principally in highly polluted areas. The study of its photochemistry is important because of its possible toxic nature and its potential for phototransformation into biologically active products. We studied the primary photophysical and photochemical degradation processes of BeP, both in solution and adsorbed on silica gel and alumina, acting as models for the atmospheric particulate matter. The radical cation of BeP was characterized as an intermediate species during the photodegradation of BeP in polar solvents and adsorbed on the surfaces. The photoionization process was monophotonic, and once the radical cation was formed, it could react with water or oxygen to yield mainly diones, alcohols, and diols. In alumina, the radical yield was small, in accordance with the low photoreactivity observed on this surface. Two triplet-triplet absorption bands at 350 and 560 nm were observed in the time-resolved spectra of adsorbed BeP and in solution under nitrogen atmosphere. The BeP's triplet state, however, did not play an important role in its photoreaction pathway. The surface's pore size and the coadsorbed water affected the yields and kinetics of the intermediates but not the photodegradation mechanism.

Persistent Free Radicals from Low-Molecular-Weight Organic Compounds Enhance Cross-Coupling Reactions and Toxicity of Anthracene on Amorphous Silica Surfaces under Light

“…Relative humidity and oxygen on the AS surface might be the crucial influencing factors of ANT degradation based on previous studies. , Table shows that dry conditions (5%) promoted ANT removal in the same atmosphere, which was consistent with the previous result of Reyes et al The absorbed water on the AS surface may block active sites, ,, resulting in slowing ANT removal reactions. The k obs values of ANT exhibited no significant differences in any atmosphere as RH was >5%, which was in line with the study of Fioressi and Arce .…”

“…Briefly, ANT was excited from the ground state to the excited singlet state ( 1 ANT*) after absorbing light energy, and then 1 ANT* can relax to the triplet state ( 3 ANT*) through the intersystem crossing process. 3 ANT* could further transfer energy or electron to O 2 to form 1 O 2 or superoxide (O 2 •– ) and ANT radical cation (ANT •+ ) . Therefore, the quenching experiments were further employed to the contributions of ROS and energy transfer to ANT removal.…”

In Situ Investigation the Photolysis of the PAHs Adsorbed on Mangrove Leaf Surfaces by Synchronous Solid Surface Fluorimetry

“…And the higher the quantity of the PAH adsorbed on the leaf surfaces, the more the excited states or polymer molecules of PAH formed. In conclusion, the number of photons striking the leaf surfaces decreased, and thereby decrease the photolysis rate of the PAH adsorbed on mangrove leaf surfaces [36] – [39] . However, the equations obtained in this work were not generalized.…”

“…Thus, it was reasonable that the photolysis rate of the same PAH adsorbed on mangrove leaf surfaces was slower than in water. Moreover, some of the lipoidal compounds on plant leaves could adsorb and reflect the UV light [26] , [27] , [36] – [38] . And the number of UV photons striking to the PAH adsorbed on the mangrove leaf surfaces decreased, and thereby slowed down the photolysis rate of the adsorbed PAH.…”

Electron-accepting potential of solvents determines photolysis rates of polycyclic aromatic hydrocarbons: Experimental and density functional theory study

“…The IP values of the two PAHs* were smaller than those of the studied solvents (with IP > 9.6 eV, shown in Table 1), implying that the PAHs* are electron donors. Some previous studies [34][35][36] also indicated that photoinduced electron transfer is a possible photodegradation path of PAHs. Therefore, the solvents could be involved in the photodegradation process as electron acceptors.…”