Model-free transformation kinetics for ZnS quantum dots synthesized via colloidal reaction

Zinc sulfide (ZnS) quantum dots (QDs) were prepared by a simple non-toxic colloidal reaction of zinc acetate dehydrate and sodium sulfate in the presence of sodium dodecyl sulfate (SDS) acting as an anionic coordinated capping material. Differential scanning calorimetry (DSC) measurements for the synthesized ZnS QDs were carried out at various heating rates. The recorded DSC curves exhibit overlapped exothermic peaks accomplishing several nano-sizes groups of the synthesized single-compositional ZnS cubic phase. The temperature at maximum rate of transformation for the main exothermic peak exhibits a monotonic shift to higher temperatures (324-388 °C) as the heating rate increased from 5 °C/min to 30 °C/min, suggesting that the growth process has a kinetic effect. The kinetics of such non-isothermal growth process was studied by applying a model-free isoconversional approach. The obtained values of the activation energy and reaction mode were used to identify the growth mechanism.