Colloidal cadmium sulfide particle

H.J. Watzke, J.H. Fendler, Quantum size effects of in situ generated colloidal cadmium sulfide particles in dioctadecyldimethylammonium chloride surfactant vesicles, J. Phys. Chem. 91 (1987) 854. 

Let us add here that the fabrication of polycrystalline semiconductive films with enhanced photoresponse and increased resistance to electrochemical corrosion has been attempted by introducing semiconductor particles of colloidal dimensions to bulk deposited films, following the well-developed practice of producing composite metal and alloy deposits with improved thermal, mechanical, or anti-corrosion properties. Eor instance, it has been reported that colloidal cadmium sulfide [105] or mercuric sulfide [106] inclusions significanfly improve photoactivity and corrosion resistance of electrodeposited cadmium selenide. 

Rafaeloff, R., Tricot, Y.-M., Nome, F., and Fendler, J.H., Colloidal catalyst coated semiconductors in surfactant vesicles In situ generation of rhodium-coated cadmium sulfide particles in diocta-decyldimethylammonium halide surfactant vesicles and their utilization for photosensitized charge separation and hydrogen generation, J. Phys. Chem., 89, 533,1985. 

Specifying a reasonable N value and substituting in Eq. (3) the value a = 1.09 0.24 J/m2 estimated from the data of [4], one may determine by Eq. (3) the equilibrium size of the colloidal particle, which appears to be dependent on the stability constant of the complex. A detailed analysis of this calculation is reported elsewhere [2]. The a value was estimated as follows. According to the data of [4], the range of solubility product (SPcas) values was found from the condition of dissolving the cadmium sulfide particles of size 2R = 25 A by the added Na2EDTA and concurrent stability of these particles to alkalization ... 

Farmer and Patten have modified the composition of the colloidal initiators to encapsulate cadmium sulfide particles in a shell of silica [340]. The ATRP initiating groups were introduced by condensing functional monoalkoxysilanes containing 2-bromopropionate groups to the silica surface. The ATRP of St from these core-shell colloidal initiators yielded an array of luminescent particles in a matrix of tethered pSt. 

The enhancement can be explained also by an excitation transfer from Si nanocrystallites to Eu ions. Other authors [10] have shown similar results by comparing the PL of Eu in silica gel and in silica gel with colloidal cadmium sulfide. They show that CdS nanoparticles enhanced Eu fluorescence due to energy transfer from a surface trap in the CdS particles to Eu ions. 

P. Lianos and J. K. Thomas, Small cadmium sulfide particles in inverted micelles, J. Colloid Interface Sci. 117,505-512(1987). 

Cadmium sulfide has been proposed as a catalyst for the splitting of water by sunlight In these studies, the CdS particles were loaded with colloidal RuO in... 

Colloids of semiconductors are also quite interesting for the transmembrane PET, as they possess both the properties of photosensitizers and electron conductors. Fendler and co-workers [246-250] have shown that it is possible to fix the cadmium sulfide colloid particles onto the membranes of surfactant vesicles and have investigated the photochemical and photocatalytic reactions of the fixed CdS in the presence of various electron donors and acceptors. Note, that there is no vectorial transmembrane PET in these systems. The vesicle serves only as the carrier of CdS particles which are selectively fixed either on the inner or on the outer vesicle surface and are partly embedded into the membrane. However, the size of the CdS particle is 20-50 A, i.e. this particle can perhaps span across the notable part of the membrane wall. Therefore it seems attractive to use the photoconductivity of CdS for the transmembrane PET. Recently Tricot and Manassen [86] have reported the observation of PET across CdS-containing membranes (see System 32 of Table 1), but the mechanism of this process has not been elucidated. Note, that metal sulfide semiconductor photosensitizers can be deposited also onto planar BLMs [251],... 

Substitution of the lattice cadmium ions in a CdS colloidal particle by the ions of another metal is often accompanied by the formation of the so-called coated particles CdS/MexSy. Such particles are readily produced via the substitution of cadmium ions by other ions if only their sulfide are less soluble compared to the cadmium sulfide. Our studies on the luminescence properties of such particles and regularities of their luminescence... 

Spanhel, L., H. Weller and A. Henglein (1987). Photochemistry of semiconductor colloids. 22. Electron ejection from illuminated cadmium sulfide into attached titanium and zinc oxide particles. Journal of the American Chemical Society, 109, 6632-6635. 

A in particle size distribution curves. Colloidal gold, silver, platinum and platinized cadmium sulfide were generated in Aerosol-OT reversed micelles or in microemulsions by in situ photolysis of the appropriate ions (Figure 3.15). Under suitable conditions, each assembly contained approximately eight Au " ions, which firstly led to the formation of Aug clusters. ... 

Preparation of Colloidal CdS. Colloidal CdS samples were prepared by precipitation from an aqueous surfactant solution. Aqueous sodium sulfide was slowly added to a stirred solution of cadmium chloride plus surfactant, which produced a clear, yellow-orange colloidal sample of cadmium sulfide. The particle sizes of the colloids were on the order of 250-300 A in radius. There was no observable change in the particle radius upon addition of MV to the CdS colloids. Furthermore, in the absence of surfactant CdS rapidly precipitates from solution. 

Photochemistry of Titanium Dioxide Colloids. Another semiconductor colloid used in our studies is titanium dioxide which has a band gap of 3.2 eV. As in the case of cadmium sulfide, excitation of aqueous suspensions of this particle leads to electron-hole pair separation which can be intercepted with suitable redox reagents. In the absence of externally added solutes, the photogenerated electron-hole pair recombines to give the starting material and the light energy is dissipated to the medium as heat. Two types of TiOj samples are used in this study. TiOj prepared at high temperature (80°C) which behaves very similarly to commercial samples, and TlOj prepared at low temperature (35°C) which has a particle size of 300 100 A radius and shows different properties. 

Matijevic, E. and Wilhehny. D.M., Preparation and properties of monodispersed spherical colloidal particles of cadmium sulfide. J. Colloid Intetf. Sci., 86, 476, 1982. 

For electronics and nano-optical application particles are preferably composed out of a conducting metal such as gold, silver, copper, platinum, or at least a semi conductor such as silicon, cadmium sulfide, cadmium selenide or zinc oxide. To achieve efficient collective behavior noble metal colloids of either a high homogeneity in size and shape are required or a deep understanding of excitation modes (particle plasmons and extended plasmons, Figure 2) within particle assemblies is necessary. 

Bigham, S.R. and Coffer, J.L. (2000). Thermochemical passivation of DNA-stabUized Q-cadmium sulfide nanoparticles. J. Cluster Sci. 11 (2), 359-372. Caruso, F. (2001). Nanoengineering of particle surfaces. Adv. Mater. 13 (1), 11-22. Hayat, M.A. (1989). Colloidal Gold Principles, Methods, and Applications, New York Academic. 

The luminescence of macrocrystalline cadmium and zinc sulfides has been studied very thoroughly The colloidal solutions of these compounds also fluoresce, the intensity and wavelengths of emission depending on how the colloids were prepared. We will divide the description of the fluorescence phenomena into two parts. In this section we will discuss the fluorescence of larger colloidal particles, i.e. of CdS particles which are yellow as the macrocrystalline material, and of ZnS particles whose absorption spectrum also resembles that of the macrocrystals. These colloids are obtained by precipitating CdS or ZnS in the presence of the silicon dioxide stabilizer mentioned in Sect. 3.2, or in the presence of 10 M sodium polyphosphate , or surfactants such as sodium dodecyl sulfate and cetyldimethylbenzyl-ammonium... 

Fig. 2.2 shows the adsorption spectra of a colloidal CdS solution prepared by the above method in the presence of cadmium complexones of various nature. The position of the colloids adsorption band indicates that the equilibrium size of the colloidal particles decreases as the stability constant of the complex increases. This may relate to the fact that it is precisely the decay rate of the cadmium complex that determines the number of nuclei N and, hence, the size of the forming particles. This is supported by the fact that with the fixed initial (before the addition of the sulfide anion and after the addition of the ligand) concentration of activated Cd2+ (lg[CdL]/[Cd2+]) = const and [Cd°] = const), for complexones of various nature, the sizes of colloidal particles differ the stronger the initial complex, the smaller the particle size. 

The metals have the tendency to form compounds of low solubility with the major divalent cations (Pb, Cd being found in natural water. Hydroxide, carbonate, sulfide, and, more rarely, sulfate may act as solubility controls in precipitating metal ions from water. A significant fraction of lead and, to a greater extent, cadmium carried by river water is expected to be in an undissolved form. This can consist of colloidal particles or larger undissolved particles of lead carbonate, lead oxide, lead hydroxide, or other lead compounds incorporated in other components of surface particulate matter from runoff. The ratio of lead in suspended solids to lead in dissolved form has been found to vary from 4 1 in rural streams to 27 1 in urban streams. The US Environmental Protection Agency (USEPA) has reported Maximum Contaminant Levels in water that are permissible to be 0.005 m L for cadmium and 0.015 mg/L of lead. ... 

Fig. IV-14. Electron micrographs of some characteristic monodispersed colloidal particles a - zinc sulfide (ZnS), b - hematite (a-Fe203), c - cadmium carbonate (CdC03). Courtesy of Professor Egon Matijevic...

One of the other early investigations came from Lianos and Thomas [346] who used AOT micelles in heptane for the synthesis. Two solutions, one containing cadmium perchlorate hexahydrate and another containing sodium sulfide nonahydrate, were prepared. Mixing of the two solutions in the reverse micelles produced small particles of CdS. The solutions were bubbled with nitrogen gas for deoxygenation and avoiding colloidal sulfur formation. The same authors used... 

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