Ultrasound-induced formation and dissolution of colloidal CdS

Abstract

The sonochemical formation of Q-state CdS colloids and the dissolution of larger colloidal CdS particles are described. In systems containing 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 on the thiol group of the mercaptan, although there is evidence that the local heating from ultrasound also contributes to H₂S formation. The colloid particles produced by the ultrasound process clearly show quantum 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 reaction of H₂O₂ and O₂⁻ with the colloids. It has been found that the reaction can be inhibited by the addition of Na₂S to the colloidal solution. Results also show that the reactions involved in the presence of Na₂S are complex and that sulfur oxyanions most likely partake in the overall scheme once they are formed.