There have been relatively few detailed studies of
PAH photochemical degradation mechanisms and
products at solid/air interfaces under controlled
conditions. Results from mechanistic studies on
particulate simulants are important in understanding
the fates of PAH sorbed on similar materials in
natural settings. In this study, the photolysis of
phenanthrene (PH) on silica gel, in the presence of
air, has been carefully examined. Once sorbed
onto the silica surface, PH is not observed to repartition
into the gas phase, even under vacuum, and dark
reactions of PH are not observed at the silica/air
interface. Photolysis (254 nm) of PH leads to the
formation of 2,2‘-biformylbiphenyl (1),
9,10-phenanthrenequinone (2),
cis-9,10-dihydrodihydroxyphenanthrene (3), benzocoumarin (4),
2,2‘-biphenyldicarboxylic acid (5), 2-formyl-2‘-biphenylcarboxylic
acid
(6), 2-formylbiphenyl (7),
1,2-naphthalenedicarboxylic acid (8), and phthalic acid (9). These
products
account for 85−90% of the reacted PH. The photoproducts are independent of excitation wavelength
(254 and 350 nm), and the reaction proceeds entirely
through an initial step involving the addition of singlet
molecular oxygen to the ground state of phenanthrene
with subsequent thermal and/or photochemical reactions of the initially formed product. Singlet
molecular oxygen is produced through quenching of
the lowest triplet state of PH at the silica gel/air
interface. The high material balance and detailed
mechanistic information provided by this study serve
as a standard for comparisons with the products
and mechanism of PH photochemical oxidation on
environmentally derived inorganic oxide
particulates.
Photolysis of naphthalene on the surface of Si02 under an atmosphere of air produces phthalic acid as the only major photoproduct, accounting for 49Yo of the consumed naphthalene. Photolysis on A1201 also produces phthalic acid, in 3 1% yield. Photolysis of 1 -methylnaphthalene on SiO, proceeds under similar conditions to produce 2-acetylbenzoic acid (35%) as the major photoproduct with the production of a small amount of I-naphthaldchyde (6%). 1 -Cyanonaphthalene does not photooxidize under similar conditions. The presence of oxygen is necessary for the photodecomposition of naphthalene and 1 -methylnaphthalene to proceed. Superoxide formed from the photolysis of naphthalene at the SiOJair interface is readily observed by electron paramagnetic resonance spectroscopy. In the absence of naphthalene no superoxide is observed. A mechanism involving electron transfer from the S, state of the naphthalene to 0, is proposed on the basis of these observations and related literature precedent.Rev. 8. 135-157. 24. Trifiro, F., A. Vaceari, E. Giamello and 0. Pedulli (1992) The nature of active sites in catalytic ammoximation of cyclohexanone to the corresponding oxime on amorphous silica: E. P. K. Investigations. c'utul. Lett. 13,[21][22][23][24][25][26] 6398-6405.Cutd. 61, 267-269.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.