What Is the Effective Charge of TGA-Stabilized CdTe Nanocolloids?

Abstract

The surface charge of semiconductor nanoparticles, Q, is an important parameter which determines their electrokinetic behavior, stability in water and polar solvents, functions of optical and electronic devices, self-assembly properties, and interactions with cell membranes. We have developed a simple method for quantitative determination of Q in their native aqueous environment. The method does not require the knowledge of exact atomic structure or make assumptions about effects of drying on charge distribution. The method is based on titration of nanoparticle dispersion with a solution of oppositely charged polyelectrolyte. The point of complete neutralization is recognized as an inflection point on the dependence of fluorescence intensity on the amount of polyelectrolyte added. Thioglycolic acid-stabilized CdTe nanoparticles 2 nm in diameter were found to carry an average Q from -2.6 to -5.5 for pH 7.5 to 10, respectively. This charge is found to be smaller than that calculated theoretically for an analogous structure (i.e., Q = -8), presumably due to adsorption of Cd(2+) ions on the stabilizer shell and on Te atoms with unsaturated valence located on the side planes of CdTe tetrahedrons.

Controllable synthesis of thioglycolic acid capped ZnS(Pn)0.5 nanotubes via simple aqueous solution route at low temperatures and conversion to wurtzite ZnS nanorods via thermal decompose of precursor

“…However, here we used TGA not only as the sulfur source but also as the thiol-capping agent to the sulfide particles' surface. It was reported that, at low pH, thiol was complexed to sulfide particles: in contrast, under an alkaline environment, thiol was more strongly complexed to free metal ions [32,33]. In this experiment, with addition of TGA solution, the pH of the solution was adjusted to 8.…”

Spontaneous polarization effects in nanoscale wurtzite structures

“…In addition to the usual large, and technologically important, spontaneous polarizations in many wurtzite structures, this paper demonstrates that surface terminations are important in determining spontaneous polarizations in nanostructures. In addition, these effects have been estimated at the order-of-magnitude level for spherical quantum dots in view of the growing scientific and technological interests in colloidal quantum dots which have approximately spherical geometries [9][10][11][12]. These results take on enhanced significance in view of recent results on the varying charge states of colloidal nanocrystals [10] as well as theoretical efforts aimed at understanding the polarization states of colloidal nanocrystals [13].…”

Semiconductor nanowires self-assembled from colloidal CdTe nanocrystal building blocks: optical properties and application perspectives

“…31 At the same time, the carboxylic acid groups of the TGA ligand shell on CdTe NCs create a net negative charge reaching 2 to 10 electrons per particle. 32 This results in a large repulsive force between NCs in their original aqueous solution. Partial removal of TGA stabi lizers from the NC surface due to treatment with methanol reduces the repulsive forces between NCs, causing them to form linear aggregates and later on to fuse into thicker, polycrystalline wires.…”