ULTRASOUND-INDUCED FORMATION AND DISSOLUTION OF COLLOIDAL CDS

The sonochemical formation of Q-state CdS colloids and the dissolution of larger colloidal CdS particles are described. In systems containin g mercaptopropionic acid, the action of ultrasound produces H2S and in the presence of Cd2+(aq) ions, colloidal CdS is formed. The mechanism for the production of H2S appears to be predominantly H-atom attack o n the thiol group of the mercaptan, although there is evidence that th e local heating from ultrasound also contributes to H2S formation. The colloid particles produced by the ultrasound process clearly show qua ntum size effects and are estimated to be less than 3 nm in diameter. The dissolution of colloidal CdS at pH 10.5 appears to be due to the r eaction of H2O2 and O-2(-) with the colloids. It has been found that t he reaction can be inhibited by the addition of Na2S to the colloidal solution. Results also show that the reactions involved in the presenc e of Na2S are complex and that sulfur oxyanions most likely partake in the overall scheme once they are formed.