The effect of cadmium ion adsorption on the growth of CdS nanoparticles at colloidal silica particle interfaces in binary liquids

Abstract

Adsorption isotherms have been determined for the binding of Cd2+ onto the surfaces of hydrophilic A200 SiO2 and hydrophobic R972 SiO2 particles dispersed in ethanol (1)-cyclohexane (2) mixtures at ethanol mole fractions of χ1 = 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 particles provided information on their quantity, absorption edges, optical band gaps, and mean diameters. Good correlations have been obtained between the adsorption isotherms and size of the CdS particles as well as between the adsorption isotherms and the amount of CdS formed. The smallest CdS particles (ca. 6 nm diameter) have been obtained on the surfaces of SiO2 particles dispersed in ethanol (1)-cyclohexane (2) mixtures at ethanol mole fractions of χ1 = 0.05. More CdS particles have been observed to coat the hydrophilic A200 SiO2 than the hydrophobic R972 particles. In the χ1 = 0.10 ethanol (1)-cyclohexane (2) liquid mixtures up to 10% of the SiO2 surface can be covered by CdS nanoparticles. Immersion wetting enthalpy measurements in methanol established the surface of the SiO2 particles to be hydrophilic, which became partially hydrophobic upon and the binding of cadmium ions and hence upon the subsequent-formation of CdS.