Kinetic-Dependent Crystal Growth of Size-Tunable CdS Nanoparticles

Abstract

The general study of crystal growth of spherical-like nanoparticles involves monitoring the kinetics during the progress of the reaction. In the case of cadmium sulfide (CdS), cadmium acetate and sodium sulfide are employed as starting reagents that are dissolved in different solvents (ethylene glycol, glyme, diglyme, and trioctylphosphine) to study the solvent effect on monomers, nucleation rates, and the quality of the seeds. Trialkylphosphine oxide (alkyl = ethyl or octyl) is chosen as a surfactant to passivate the surface of CdS nanoparticles. We propose a kinetic approach model to illustrate the unreported time-evolved crystal growth mechanism observed in this case. An experimental value for the diameter of critical volume (V c), a nanosized volume with a relative minimum surface-volume tension and considered a temporal stable stage (r = 5.7 nm in this case), is derived from transmission electron microscopy images. The size of the nanoparticles made by this synthesis route is tunable by variation of the reaction time and control of the reaction temperature; in addition, the resulting sizes are suitable for spectroscopic testing of electron quantum confinement. The X-ray powder diffraction data are consistent with a pure hexagonal CdS lattice and show no evidence for a mixed phase involving cubic symmetry.

Stability of core/shell quantum dots—role of pH and small organic ligands

“…2). A lower value of pK sp such as 18.8 (Yang et al 2001) provides a much larger dissolved Cd (dotted line of Fig. 2), whereas by using the same solubility product given by Smith and Martell ( 1989a) 1.0e-10…”

“…2 Concentration of dissolved Cd as function of pH. The lines represent the calculated dissolved Cd by using different parameters: solid line-pK a1 =7.0, pK a2 =13.8, pK sp =25.8 (Allison et al 1999); long dash line-pK a1 =7.0, pK a2 = 15.0 (Westerflier et al 1987), pK sp =25.8; dotted line-pK a1 =7.0, pK a2 =13.8, pK sp =18.8 (Yang et al 2001). The points represent the experimental values for an exposure time of 48 h. (Westerflier et al 1987)) a good agreement is obtained between the calculated dissolved Cd and the one obtained experimentally by using the SSCP technique (pH 4.5: 55 % of the total Cd cf.…”

The role of charged polymer coatings of nanoparticles on the speciation and fate of metal ions in the environment

“…Indeed, (a) at these conditions of pH 8.5 and 5.0×10 −7 M of Cd the solubility product is almost reached (Fig. 3), and (b) significantly larger ΔE d,1/2 were obtained for Cd in presence of the PAA-stabilized NP; at pH 8.5 the ΔE d,1/2 pH 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 (Allison and Brown 1999) or pK sp (PbS)=27.5 (Joshi 2006); long dash line -pK a1 =7.0, pK a2 =15.0 (Westerflier et al 1987), pK sp (CdS)=25.8 or pK sp (PbS)=27.5; black dotted linepK a1 =7.0, pK a2 =13.8, pK sp (CdS)=18.8 (Yang et al 2001) values were around two times larger than for the Cd-PAA complexes ( Figure S1), indicating the formation of much strong complexes, which may be non-labile. A truly remarkable result is that the binding of metal ions by the charged polymer coating of the NP is significantly higher than the binding properties of the charged polymer capsule.…”

Preparation of ZnO/CdS/BC Photocatalyst Hybrid Fiber and Research of Its Photocatalytic Properties

“…CdS, as a representative II-VI compound semiconductor, has been used as a visible-light photocatalyst [8] and also as a photosensitizer of various wide band-gap semiconductor photoanodes in photoelectrochemical cells due to its narrow direct band-gap (2.4 eV) [9]. However, it is very easy etching, resulting in the decreased service life [10,11]. The combined ZnO and CdS system in nanosize area has attracted a great deal of attention in recent years.…”

“…It can be overcome through the photocatalyst fixation instead of the recovery of the photocatalyst [10][11][12][13][14][15][16][17][18][19][20]. The key of immobilized technique is the performance of adopted immobilized carriers.…”