Ultrasonication of aqueous and micellar suspensions of anthracene fixed on silica

Degradation under ultrasound irradiation of silica supported anthracene (Ant) in aqueous suspension is studied. The initial degradation rate of Ant on silica is 28- and 6-fold lower than the degradation rate in water alone, at 506 and 20 kHz, respectively. Analysis of emission and excitation spectra demonstrates the presence of two kinds of adsorbed Ant species: a molecular form and crystals. The former species is assumed to be initially degraded at 506 kHz, while the latter species is more difficult to decompose. Specific irradiation of micro-crystals of Ant in aqueous/methanolic solution leads to the formation of CO and CO2. A pyrolytic mechanism is expected to occur on the surface of silica and the kinetic rates would depend on the chemical nature of Ant at the surface. Added surfactants decrease dramatically the degradation rates on silica, but solubilizes Ant in larger amounts than in pure water. Surfactants are pyrolysed in water with and without silica and act more as degradation inhibitors than as Ant extracting agents. (C) 2002 Elsevier Science B.V. All rights reserved.