THE EFFECT OF CADMIUM ION ADSORPTION ON THE GROWTH OF CDS NANOPARTICLES AT COLLOIDAL SILICA PARTICLE INTERFACES IN BINARY LIQUIDS

Adsorption isotherms have been determined for the binding of Cd2+ onto the surfaces of hydrophilic A200 SiO2 and hydrophobic R972 SiO2 parti cles dispersed in ethanol(1)-cyclohexane (2) mixtures at ethanol mole fractions of x(1) = 0.05, 0.10, 0.20, and 0.40. CdS nanoparticles have been generated in situ within the ethanolic nanoreactors at surfaces of SiO2 particles in the different ethanol-cyclohexane binary liquids by the addition of hydrogen sulfide. Absorption spectra of the CdS par ticles provided information on their quantity, absorption edges, optic al band gaps, and mean diameters. Good correlations have been obtained between the adsorption isotherms and size of the CdS particles as wel l as between the adsorption isotherms and the amount of CdS formed. Th e smallest CdS particles (ca. 6 nm diameter) have been obtained on the surfaces of SiO2 particles dispersed in ethanol (1)-cyclohexane (2) m ixtures at ethanol mole fractions of x(1) = 0.05. More CdS particles h ave been observed to coat the hydrophilic A200 SiO2 than the hydrophob ic R972 particles. In the x(1) = 0.10 ethanol (1)-cyclohexane (2) liqu id mixtures up to 10% of the SiO2 surface can be covered by CdS nanopa rticles. Immersion wetting enthalpy measurements in methanol establish ed the surface of the SiO2 particles to be hydrophilic, which became p artially hydrophobic upon and the binding of cadmium ions and hence up on the subsequent formation of CdS. (C) 1997 Academic Press.