Size and zeta potential of CdS nanoparticles in stable aqueous solution of EDTA and NaCl

We have studied the effect of disodium EDTA concentration on the size and zeta potential of CdS nanoparticles in a stable aqueous solution. Measurement results demonstrate that the colloidal solution remains stable at initial Cd2+ and S2- concentrations of 8 mM and initial EDTA concentrations in the range 3.2 to 16 mM. The reactant mixing sequence is shown to influence the ionic state of EDTA in solution, which in turn influences the stabilization mechanism of the CdS nanoparticles. At pH 3, we observe the formation of protonated chelates such as [CdHY](-), which may form a [-S-Cd-EDTA] ternary complex with the surface of a nanoparticle, thereby ensuring stability of the colloidal solution at a twofold excess of EDTA. Analysis of the nanoparticle size distribution evaluated by dynamic light scattering measurements indicates that the minimum hydrodynamic diameter of the nanoparticles is 10 +/- 3 nm. The corresponding zeta potential is about -20 mV.