FORMATION MECHANISM OF UNIFORM CDS PARTICLES FROM CONDENSED CD(OH)(2)SUSPENSION

The formation mechanism of uniform cadmium sulfide particles obtained in large quantities from condensed Cd(OH)(2) suspension in the presenc e of thioacetamide (TAA), gelatin and NH3-NH4+ buffer system was inves tigated. Basically, the reaction proceeded through rapid dissolution o f Cd(OH)(2) particles induced by the reaction of Cd2+ ions with S2- io ns liberated from TAA in the solution phase. It was finished in ca. 1 min under the standard conditions, 0.5 mol dm(-3) in Cd(OH)(2), 0.55 m ol dm(-3) in TAA, 1 wt% in deionized gelatin, and 1.0 mol dm(-3) NH4NO 3 at 20 degrees C and at pH 8.50 adjusted with NH3. The resulting unif orm and nearly spherical particles of CdS prepared under the standard conditions were 40 nm in mean diameter and were polycrystalline partic les consisting of randomly oriented much smaller subcrystals (8.60 nm) . Besides using the NH3-NH4+ system in generating uniform CdS particle s, employing borax/NaOH buffer system in the formation of spherical Cd S particles was also possible. It was also found that S2- ions were fu rnished through a reaction, CH3CSNH2 --> CH3CN + 2H(+) + S2-. This rea ction was excessively accelerated by the rapid consumption of S2- ions so that it is thought to be a reversible reaction. The reaction was v irtually stoichiometric and the contribution of hydrolysis of TAA was not observed. The uniform growth of the CdS particles was achieved by the controlled dissolution of the Cd(OH)(2) without aggregation of the growing CdS particles after an instantaneous nucleation. (C) 1995 Aca demic Press, Inc.