Cadmium, colloidal sulfide

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. 

Singh K, Mishra SSD (2004) Photoelectrochemical studies on colloidal cadmium sulfide containing cadmium selenide electrodeposits. Electrochem Solid State Lettate 7 A185-A186... 

Hotchandani S, Kamat P (1992) Charge-transfer processes in coupled semiconductor systems. Photochemistry and photoelectrochemistry of the colloidal cadmium sulfide-zinc oxide system. J Phys Chem 96 6834—6839... 

Meyer M, Wallberg C, Kurihara K, Fendler JH (1984) Photosensitized Charge Separation and Hydrogen-Production in Reversed Micelle Entrapped Platinized Colloidal Cadmium-Sulfide. J Chem Soc Chem Commim, pp 90-91... 

Morgan, J. R. Natarajan, L. V. Picosecond transient grating study of charge carrier dynamics in colloidal cadmium sulfide, J. Phys. Chem. 1989, 93, 5. 

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. 

Comor, M. I. and Nedeljkovic, J. M (1999). Enhanced photocorrosion stability of colloidal cadmium sulfide-silica nanocomposites. J. Mater. Sci. ILetter. 18(19), 1583-1585. 

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. 

Kamat PV, Dimitrijevic NM, Fessenden RW (1987) Photoelectrochemistry in particulate systems. 6. Electron-transfer reactions of smaU cadmium sulfide colloids in acetonitrile. JPhys Chem 91 396-401... 

Photoanodic dissolution in the presence of air and its promotion by methyl viologen was also observed for alkaline solutions of colloidal cadmium phosphide, CdjPj and cadmium arsenide, CdjAsj Bismuth sulfide, Sb Sj, photo-dissolves in the presence of air mainly according to... 

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... 

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. 

Cadmium sulfate hydrate, 4 515 physical properties of, 4 509t Cadmium sulfate monohydrate, 4 515 physical properties of, 4 509t Cadmium sulfide, 4 503, 515-516, 518, 521 colloidal precipitation color, 7 343t color and bad gap, 7 335t physical properties of, 4 509t piezochromic material, 6 607 Cadmium sulfide photodetectors, 19 137 Cadmium sulfide photoconductor, fabrication and performance of, 19 155-156... 

Robinson BH, Towey TF, Zourab S, Visser AJWG, Vanhoek A (1991) Characterization of Cadmium-Sulfide CoUoids in Reverse Micelles. Colloids Surf 61 175-188... 

Dutta P, Fendler JH (2002) Preparation of cadmium sulfide nanoparticles in self-reproducing reversed micelles. J Colloid Interface Sci 247 47-53... 

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],... 

Keywords Kinetics, photocatalysis, Cadmium sulfide, nanoparticles, colloids, electron transfer, photoreduction... 

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 ... 

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. 

Visible Light Induced Hydrogen Production from In Situ Generated Colloidal Rhodium-Coated Cadmium Sulfide in Surfactant Vesicles. The first of a series of studies (see also Refs. 505-507) exploring the use of vesicles and reverse micelles for photo-induced charge separation and HER. 504... 

The mechanism of photocorrosion seems to be the same for zinc and cadmium sulfide. For the latter it was investigated in detail for colloids [26] and crystals as discussed in the following [56]. In the absence of air, anodic photocorrosion (Eq. 15) ... 

Hydrazone cyclization and hydroalkylation [138-140] are rare examples of reactions conducted on a preparative scale, since the products were isolated in milligram amounts and not just identified in solution. As already mentioned in Section 6.2.5, photocorrosion of the semiconductor photocatalyst often prevents its use in preparative chemistry. This is very true also for colloidal semiconductors although the pseudo-homogeneous nature of their solutions allows one to conduct classical mechanistic investigations, until now they were too labile to be used in preparative chemistry [107, 141, 142]. In contrast to the above-mentioned reactions, in recent years we have isolated novel compounds on a gram-scale employing photostable zinc and cadmium sulfide powders as photocatalysts [97, 107, 143-145]. During this work we found also a new reaction type which was classified as semiconductor photocatalysis type B [45]. In contrast to type A reactions, where at least one oxidized and one reduced product is formed, type B reactions afford only one unique product, i.e., the semiconductor catalyzes a photoaddition reaction (see below). 

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. ... 

Sorption colloid flotation has shown to be capable of quantitatively separating ionic mercury from sea water at levels down to 0.02 gg/1 using a cadmium sulfide collector and octadecyltrimethylammonium chloride as a surfactant. The sea water samples need only to be acidified with hydrochloric acid. For flotation an adjustment to pH 1.0 is crucial. Mercury concentrations generally seemed to decrease with the depth of sea water 99). 

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. 

A further feature may be obtained by producing a less structured red form of cadmium sulfide. Hie red CdS colloid exhibits a red shifted emission spectrum compared to that of normal cadmium sulfide, and it also has a much longer lifetime. This gives a much longer lifetime for the electron-hole pair and larger yields of reduced product are expected from such systems. 

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. 

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