Synthesis of stable CdS nanocrystals using experimental design: Optimization of the emission

Abstract

The optimization of the synthesis of CdS nanocrystals (CdS NCs) stabilized with 3-mercaptopropionic (MPA) acid was studied using chemometric tools. All factors (variables) involved in the CdS NC synthesis were optimized. The analysed factors were the CdCl2, Na2S and 3-mercaptiopropionic acid concentrations, and the time and temperature of the reaction. First, a full factorial design was carried out to evaluate the effect of all factors and their interactions, where the analysed factors were the CdCl2, Na2S and 3-mecaptiopropionic acid concentrations, and the time and temperature of the reaction. Second, a central composite design was chosen for optimization of the factors. The optimization of the CdS NC synthesis was carried out using the fluorescence intensity of CdS NCs. The values of the factors that maximize the fluorescence intensity of the synthetized CdS NCs were a concentration range of CdCl2, Na2S and MPA of (7.96-8.49) × 10-3 mol L-1, (6.06-8.50) × 10-3 mol L-1 and (47.58-71.85) × 10-3 mol L-1, respectively, and a temperature range of (20-74) °C. Under the best conditions, the relative error was 14%. The optimized CdS NCs were purified through size selective precipitation. A fluorescence quantum yield (QY) of 1.02% was obtained. On the other hand, the bulk band gap of the CdS NCs was 2.99 eV (close to 415 nm). The synthesis of the NCs studied was reproducible and they had good fluorescence.