Formation Mechanism of Uniform CdS Particles from Condensed Cd(OH)2Suspension

Abstract

The formation mechanism of uniform cadmium sulfide particles obtained in large quantities from condensed Cd(OH)2suspension in the presence of thioacetamide (TAA), gelatin and[formula]buffer system was investigated. Basically, the reaction proceeded through rapid dissolution of Cd(OH)2particles induced by the reaction of Cd2+ions with S2−ions liberated from TAA in the solution phase. It was finished in ca. 1 min under the standard conditions, 0.5 mol dm−3in Cd(OH)2, 0.55 mol dm−3in TAA, 1 wt% in deionized gelatin, and 1.0 mol dm−3NH4NO3at 20°C and at pH 8.50 adjusted with NH3. The resulting uniform and nearly spherical particles of CdS prepared under the standard conditions were 40 nm in mean diameter and were polycrystalline particles consisting of randomly oriented much smaller subcrystals (8.60 nm). Besides using the[formula]system in generating uniform CdS particles, employing borax/NaOH buffer system in the formation of spherical CdS particles was also possible. It was also found that S2−ions were furnished through a reaction, CH3CSNH2→ CH3CN + 2H++ S2−. This reaction was excessively accelerated by the rapid consumption of S2−ions so that it is thought to be a reversible reaction. The reaction was virtually 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)2without aggregation of the growing CdS particles after an instantaneous nucleation.