Studies on the phototransformations of perylene adsorbed on non-activated silica gel and alumina as models of atmospheric particulate matter

Studies have been performed on the photochemical transformations of perylene adsorbed on non-activated silica gel of different pore sizes and alumina used as models of atmospheric particulate matter. Fluorescence, diffuse reflectance and EPR techniques have been used to study the effect of coadsorbed gases (O-2 and Ar), H2O, time of storage in the dark, and loading on the photodegradation rates and on the formation of intermediate products. Oxygen quenches significantly the fluorescence and accelerates the photodegradation rate, suggesting the participation of O-2 reactive species in the degradation reactions. The formation of photoproducts emitting and absorbing at longer wavelengths than the original compound is observed It is suggested that oxygen participates in the destruction pathways since in an argon atmosphere these bands do not appear. Adsorbed H2O induces the formation of absorbing and emitting completes with perylene or of aggregates of it formed by its displacement from the adsorption sites. New emitting intermediate products are observed in the presence of H2O. The pore sizes and the loading influence the rate of product formation The EPR spectra of irradiated samples confirm the presence of the radical cation and the photoionization of Per into Per(+) on the silica gel.