Transformation of CdS Colloids: Sols, Gels, and Precipitates

Abstract

Highly concentrated CdS colloids (about 30 wt %) are prepared in acetone through the grafting of 4-fluorophenylthiol at their surface. 19 F NMR measurements show that the controlled oxidation by an aqueous solution of hydrogen peroxide leads to a mixture of dithiol and fluorosulfonate species. Aggregation of particles produces either transparent gels or opaque precipitates, depending on the nature and the concentration of the oxidant. The sol-gel transformation results from an aggregation mechanism, which requires the release of surface groups because of their interaction with water molecules. Considering the formation of mass-fractal clusters, small-angle X-ray scattering measurements show, at least in the first steps, that the growth kinetics is in agreement with the usual reaction limited cluster aggregation mechanism previously observed in the silica system. This can be followed by a saturation effect, enhanced at low water concentration, which is due to the poisoning of the surface by chemical groups produced by oxidation.

Physical and chemical cross analyses of II‐VI semiconductor nanomaterials

“…shows the regular loss of neutral Cd(SPh) 2 from Cd 10 capping that surround a Cd 4 S 4 core previously detected by our group when doing tandem mass spectrometry [10]. This explains a mass difference of 578 between the highest specific core related species Cd 6 S 4 (Sph) 5 -at m/z 1353 Da and a capping related species at Cd 2 (SPh) 5 -at m/z 770.9 Da which corresponds to one Cd 4 S 4 neutral.…”

“…In that case, semiconducting nanocomposite materials have been mostly prepared by the inclusion of preformed particles in different types of matrix or by polymerization of precursors in hydrolytic or non-hydrolytic ways. The sol-gel technique provides the production of inorganic or mixed organic-inorganic compounds at low reaction temperature [5,6]. Due to the fact that the reactant mixture is realized at the molecular scale, the temperature of the reaction is indeed clearly lowered.…”

Sizing, stoichiometry and optical absorbance variations of colloidal cadmium sulphide nanoparticles

“…This is neatly illustrated by the work of Gacoin et al [5], where highly concentrated CdS particles were prepared as sols and transformed to gels or precipitates. Indeed, with careful tuning this gelation is analogous to that seen in silica systems.…”

A new addition to the aerogel community: unsupported CdS aerogels with tunable optical properties

“…They may further prove to be more advantageous than their bulk counterparts, which are currently employed in photocatalytic applications for detoxification of air and water, and promotion of organic reactions, such as the photoaddition of cyclopentene to a Schiff base [21]. To date, CdS has been synthesized as nanoparticles, colloids, crystals, nanoclusters, nanorods, nanowires, gels, and thin films [22][23][24][25]. However, the formation of a CdS aerogel has not been reported.…”