Investigation of dynamics of radiolytic formation of CdSe nanoparticles in aqueous solutions

摘要

The formation of cadmium selenide, CdSe, nanoparticles in aqueous solutions containing equimolar ammoniated cadmium sulfate, [Cd(NH_3)] _4SO_4 and sodium selenosulfate, Na_2SeSO _3 as the starting materials, has been investigated by electron pulse radiolysis coupled with kinetic spectrometry. The formation of CdSe nanoparticles was found to proceed through the generation of short-lived transient intermediate species having an absorption peak at 520 nm, which is formed only upon the reaction of hydrated electrons, e_(aq) with the precursor ions under deaerated conditions. The transient intermediate species decays with a weighted average rate constant, 1.2×10~7 s ~(-1). The transient intermediate species formed in the case of individual precursors did not match with the transients formed when both the precursors are taken together in the solutions under the present experimental conditions. The reaction rate constants between the precursor ions, [Cd(NH _3)_4]~(2+) and the transient intermediate species formed from [SeSO_3]~(2-) was 1.9×10~(10) M ~(-1) s~(-1). Similarly, the reaction rate constants between the precursor ions, [SeSO_3]~(2-) and the transient intermediate species formed from [Cd(NH_3)_4]~(2+) was 5.5×10~(10) M~(-1) s~(-1). This clearly indicates that the formation of CdSe nanoparticles occurs through both reaction channels. However, the major reaction channel is through the reaction of e_(aq) with the [Cd(NH_3)_4]~(2+) ions (k ≥ 3.1×10 ~(10) M~(-1) s~(-1)), as its rate constant is one order higher than that of the reaction of eaq with the [SeSO _3]~(2-) ions (k ≥ 2.3×10~9 M~(-1) s~(-1)).