Preparation and characterization of CdS and ZnS particles in nanophase reactors provided by binary liquids adsorbed at colloidal silica particles

Determinations of adsorption excess isotherms of silica particle dispersions in ethanol - cyclohexane and in methanol-cyclohexane binary mixtures have established the formation of 0.5-5.0 nm thick alcohol rich adsorption layers at the silica particle interface. The adsorption layers on silica particles, formed in methanol-cyclohexane = 0.01:99.99 (mol/mol) and ethanol-cyclohexane = 0.05:99.95 (mol/mol), were used as nanophase reactors for the in situ generation of size-quantized CdS and ZnS particles. The semiconductor particles were generated by the addition of H2S to silica particle dispersions which contained different concentrations of Cd2+ or Zn2+. The smallest semiconductor particles were generated in dispersions which contained the least amount of precursors. Absorption spectrophotometry, small-angle X-ray scattering, rheological, and calorimetric measurements were used to characterize the dispersions. The presence of semiconductor particles increased the viscosities and decreased the immersion wetting enthalpies of the silica dispersions, indicating strong interparticle interactions.