Synthesis, Photoluminescence, and Adsorption of CdS/Dendrimer Nanocomposites

Abstract

CdS/dendrimer nanocomposites can be synthesized from methanolic Cd(2+) and S(2-) with amine-terminated polyamidoamine dendrimers of generation 8 (G8NH(2)) as stabilizers. By controlling the preparation conditions, nanoparticles with diameters < or = 2 nm can be obtained with a narrow size distribution. They show blue photoluminescence at approximately 450 nm. We studied the effects of various additives on the photoluminescence and elucidated its mechanism. Stable aggregates of two to three G8NH(2) molecules with several CdS nanoparticles form; the particles are located at the surface of the G8NH(2) molecules. The adsorption of the CdS/G8NH(2) nanocomposites on flat substrate surfaces is determined by the substrate chemistry. The hydrophilic nature of G8NH(2) results in weak affinity to graphite but strong affinity to hydroxy-terminated substrates such as mica, oxidized silicon wafers, and carboxylate-terminated monolayers. Patterning of nanocomposites on these hydrophilic substrates is achieved by the microcontact printing method. We propose to use only one molecule, a large dendrimer, to control the nanoparticle formation and also the immobilization of the synthesized nanoparticle/dendrimer composites.

Controlled Growth of CdS Nanocrystals: Core/Shell viz Matrix

“…The generation of CdS nanoparticles could also be identified from both the color change and the UV-Vis spectrum of the as-prepared products. For bulk CdS and ZnS, the absorption edges are at 500 and 335 nm, corresponding to energy gaps 2.5 and 3.7 eV, respectively [16]. The obtained yellow solution showed an absorption onset at about ~415 nm in nanomatrix and ~400 nm in core/shell (Figure 2), blue shift in the absorption edge from the corresponding bulk value, implies the quantum confinement effect of the CdS nanoscale particles [17].…”

Filamentous supramolecular structures with polyelectrolyte and cadmium sulfide

“…The CdS likely forms near the surface of the dendrimer, as Cd 2+ mainly interacts with the primary amine groups. 22,23 As the G9 dendrimer with 13 nm is quite large compared to the visible CdS particles (2-3 nm), it is impossible, due to steric reasons, that only one CdS particle is attached to one dendrimer in the chain. Fahmi et al 12 gave an interpretation of a conformational change towards a more anisotropic dendrimer structure in a system with generation 4 PPI dendrimer.…”

Bottom‐Up Synthesis and Top‐Down Organisation of Semiconductor and Metal Clusters on Surfaces

“…[6,7,[15][16][17] When amine-based dendrimers are employed, their protonation has a pronounced effect on the shape, number and location of the formed nanocrystals. Good examples are near-spherical, amine-terminated PAMAM [po-ly(amidoamine)] dendrimers of generations 4 (G4NH 2 ) and 8 (G8NH 2 ), where the repeat unit is N-(CH 2 CH 2 -CONH-CH 2 CH 2 ) 2 and the terminal groups are primary amines (NH 2 ).…”

“…for optical measurements) this removal is neither required nor an advantage, such as for photoluminescing CdS clusters at dendrimers. [6,7] The physical properties depend mainly on the cluster size and nature. Thus, while metal clusters reach the limit of quantised conductivity only for very small diameters (Ͻ2 nm), even relatively large semiconductor clusters (tens of nanometres) show quantised en-face.…”