Effect of the composition of the reaction mixture on the preparation of L-cysteine-stabilized CdS nanoparticles and their optical properties

Abstract

A study was carried out on the dependence of the optical properties such as the maxima in the absorption and luminescence spectra, Stokes shift, and quantum yield on the composition of the three-component Cd 2+ -L-Cys-S 2-reaction system under synthesis conditions at 298 ± 2 K and pH 7. Equations describing the dependence of the position of the maximum in the luminescence and absorption spectra of solutions on their composition were obtained by mathematical planning using the Scheffe simplex-lattice design and treatment of the data. The region of compositions for unstable colloidal solutions was determined.Decreasing the size of semiconductor crystals to a size comparable to the region of delocalization of the electron-hole pair substantially alters their physical properties and expands the scope for their practical application. Nanosized cadmium sulfide is a leading material both relative to the number of studies of the interrelationship between the method of preparation of the nanoparticles (NP) and their size and properties and to the scope of their use in optical electronics, photocatalysis, analytical chemistry, biology, and medicine (as biolabels) [1]. In many studies, special attention has been focused on cadmium sulfide nanoparticles stabilized by the biocompatible amino acid L-cysteine (L-Cys) obtained in aqueous solution [2][3][4][5][6][7]. Besides the pH of the medium, the ratio of the amounts of precursors, ionic composition of the solution, and preparation temperature have been varied, leading to a clear-cut understanding of the effect of concentration. As a rule, correlations have generally been sought upon varying the concentration of one of the precursors and holding the concentrations of the others constant. Attempts for a broader understanding of the effect of surfactants (with L-cysteine or glutathione as the stabilizer and bistrimethylsilyl sulfide as the sulfidizing agent) on the width of the forbidden band of CdS NP in the solution pH range from 4 to 10 were undertaken only by Kalasad et al. [7], who used a statistical design for the experiment.In the present work, we have established general rules for changing the optical properties and shape of cadmium sulfide NP obtained in a three-component system consisting of Cd 2+ , S 2-, and L-Cys upon broad variation of the ratios relating the 0040-5760/11/4702-0101

Biomanufacturing of CdS quantum dots

“…The relatively large Stokes shift is typical of L-cysteine capped CdS QDs in aqueous solution as reported previously. 38,39 It is likely that the as-produced QDs are capped with L-cysteine due to the relatively high L-cysteine concentration in the media, as well as the requirement of L-cysteine for synthesis.…”