Abstract
Research into the use of ultrasound in environmental protection has received much attention with the investigations focusing on harnessing of cavitational effects for the destruction of biological and chemical pollutants in water. On the other hand, sonochemical synthesis has been applied for producing a wide variety of noble materials from aqueous solutions. In both applications, there are often encountered cases where the presence of particulate matters could play an important role. In this paper, the sonochemical degradation of methyl orange in suspensions of alumina powders was investigated (Fig.1). The system was selected as a model to understand the influence of particles on the chemical effects of ultrasounds in aqueous solution. The results showed that the addition of 0.5 - 5g/L of coarse alumina powders enhanced the rate of sonochemical degradation of methyl orange up to 50% (Fig.2). The enhancement was not obvious in suspensions of finer alumina powders having average diameters of a few micrometers. The addition of large amount of alumina powders exceeding 5g/L suppressed the degradation reaction due to the shielding and scattering of ultrasound radiation by the particles. The mechanism of the enhancement of sonochemical reaction in the suspension is not clear at this stage, but the possible explanations are as follows; i) increase in the number of cavitational bubbles at the rough surface of suspended particles, ii) mechanochemical activation of the particle surface by the frequent collisions between the particles, and iii) increase of effective reaction volume by the redistribution of ultrasonic radiation field by random movement of particles.
