Elemental Reaction Steps between Elemental Sulfur and Metal Carboxylate during the Synthesis of Metal Sulfide Nanocrystals in Hydrocarbon Solvents

The reaction between elemental sulfur and metal oleate in hydrocarbon for synthesizing metal sulfide colloidal quantum dots (CQDs) was investigated. By utilization of refined signals obtained from Fourier transform infrared (FTIR) spectroscopy, accurate concentrations of oleate and oleic acid were quantified. Two distinct reaction processes with different kinetics and asynchronous changes in the concentrations of oleate and oleic acid were observed. The study of sulfur treatment on CQDs identified the first reaction process as a reaction between Cd(Ol)2 and the in situ-formed preliminary reactive products (C x H y S n ) of elemental sulfur. These species had high reactivity toward metal carboxylate, producing metal sulfide units, oleic acid, and lower reactive species (C x H y-2S n -1). The second process referred to the reaction between C x H y-2S n -1 and metal carboxylate to produce a metal sulfide unit and oleic acid. Owing to the fewer hydrogen and sulfur atoms, this process was much slower and had more asynchronous changes in the concentrations of oleate and oleic acid. Reactions employing different metal ions demonstrated the reaction between reactive sulfur species and metal carboxylate was a metal ion-assisted hydrogen transfer process. These dramatically different reaction processes not only influenced the growth but also affected the photoluminescence properties of metal sulfide nanocrystals.