2,4,6-triphenylpyrylium ion encapsulated within Y zeolite as photocatalyst for the degradation of methyl parathion

2,4,6-Triphenylpyrylium ion (TP+) encapsulated inside the supercages of Y zeolite (TPY) can efficiently effect the photocatalytic degradation of methyl parathion in aqueous solutions. Comparison of the performance of TPY with that of TP+ deposited on amorphous silica has shown that the zeolite host contributes to the efficiency of the system by stabilizing TP+ avoiding its nucleophilic ring opening and by absorbing the organic pollutant from the aqueous phase and concentrating it in the interior of the solid. Although TPY does not undergo irreversible bleaching after three consecutive irradiations, its activity is largely reduced probably due to blockage of the zeolite micropores by adventitious reagents and products. Up to 75% of the original activity can be regained by simple solid-liquid extraction. Concerning the mechanism of the photodegradation, it has been ruled out the intermediacy of singlet oxygen as well as a direct photoinduced electron transfer between excited TP+ and methyl parathion. instead, evidence has been presented for the need of O-2 as Coreagent as well as the involvement of radicals. (C) 1999 Elsevier Science Ltd. All rights reserved.