The critical role of surfactants towards CdS nanoparticles: synthesis, stability, optical and PL emission properties

Abstract

a Cadmium sulfide (CdS) nanoparticles (NPs), prepared by a convenient chemical precipitation method, have been characterized using techniques such as TEM, XRD, zeta potential, absorption and photoluminescence (PL) emission spectroscopy to establish the structure directing role of different cationic and anionic surfactants and their impact on the nanoparticles stabilization. In the synthesis of the CdS NPs, cadmium acetate and sodium sulfide, employed as starting reagents, were dissolved in aqueous solutions of different surfactants to study the effect of their structures on the nucleation, growth, optical and PL emission properties of the NPs. By varying the surfactant species, the CdS NPs have significantly different optical and PL emission properties despite being produced under similar reaction conditions. Depending on the surfactant structure, the growing CdS NPs were stabilized by the surfactants to different extents.For example, in the surfactant with the longest chain length (e.g. cetyltrimethylammonium bromide; CTAB), the CdS NPs were most stable, whereas using a surfactant with a smaller chain length i.e. DTAB, the NPs were unstable for even 1 h. On the other hand, anionic surfactants of even smaller chain lengths were able to stabilize the CdS NPs for quite long times. The generalized study of growth of spherical CdS NPs involves monitoring the kinetics during the progress of the reaction. Additionally, an interesting prominent effect of surfactant structure on the PL emission properties of the NPs has been established under identical reaction conditions.

Varying photoluminescence emission of CdS nanoparticles in aqueous medium: A comparative study on effect of surfactant structure

“…The effectiveness of the cationic and anionic surfactants in controlling the shape and size of CdS NPs has been successfully established in our earlier reports [24,25]. The Zeta potential measurements established that the NPs has been stabilized through head group adsorption of surfactants over the NP's surface and stabilization tendencies of the surfactants have been mainly governed by the hydrophobic chain length.…”

“…It has already been established that the surfactant molecules interact with surface of CdS NPs and thereby modulate their emission properties [24,25]. The changes in emitting states of CdS NPs during growth and/or adsorption of surfactants can be useful in understanding the origins of PL properties.…”

“…The percentage enhancement in PL emission intensity has been presented in Table 1. On the basis of earlier reported UV-Vis absorption studies on similar samples [25], the CdS has been bleached in aqueous solution to produce smaller NPs. These restructured CdS NPs therefore will have certain different surface structure due to surface dissolution and re-adsorbed surfactants.…”

Freeze-drying storage method based on pectin for gold nanoparticles

“…Absolute Z potential values above 30 mV provide good stability, because at these conditions, nanoparticles tend to repel each other. 24 This behavior is due to the adsorption of ions at the nanoparticle surface. The Z potential values for AuNPs synthesized with ascorbic acid and sodium citrate without pectin were À19.50 and À0.058 mV, respectively, far below the stability limit, which explain the growth and agglomeration observed in UV-vis and TEM.…”

Photoactivation, photobleaching and photoetching of CdS quantum dots − Role of oxygen and solvent

“…It has been shown that the surfactant-solvent interactions may significantly affect the optical properties of CdS nanoparticles [26,27]. Reaction mechanism and the efficiency of photoetching or photoactivation and degradation are also likely to be affected by the surface composition and passivation of nanoparticles [28].…”