Cadmium sulfide particle

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. 

Baral S, Fojtik A, Weller H, Henglein A (1986) Photochemistry and radiation chemistry of coUoidal semiconductors. 12. Intermediates of the oxidation of extremely small particles of cadmium sulfide, zinc sulfide, and tricadmium diphosphide and size quantization effects (a pulse radiolysis study). J Am Chem Soc 108 375-378... 

Sobczynski A, Bard AJ, Campion A, Fox MA, MaUouk T, Webber SE, White JM (1987) Photoassisted hydrogen generation platinum and cadmium sulfide supported on separate particles. J Phys Chem 91 3316-3320... 

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. 

Since the photophoretic force depends on the electromagnetic absorption efficiency Q y , which is sensitive to wavelength, photophoretic force measurements can be used as a tool to study absorption spectroscopy. This was first recognized by Pope et al. (1979), who showed that the spectrum of the photophoretic force on a 10 foa diameter perylene crystallite agrees with the optical spectrum. This was accomplished by suspending a perylene particle in a Millikan chamber with electro-optic feedback control and measuring the photophoretic force as a function of the wavelength of the laser illumination. Improvements on the technique and additional data were obtained by Arnold and Amani (1980), and Arnold et al. (1980) provided further details of their photophoretic spectrometer. A photophoretic spectrum of a crystallite of cadmium sulfide reported by Arnold and Amani is presented in Fig. 11. 

Towey TF, Khanlodhi A, Robinson BH (1990) Kinetics and Mechanism of Formation of Quantiun-Sized Cadmium-Sulfide Particles in Water Aerosol-Ot Oil Microemulsions. J Chem Soc Faraday Trans 86 3757-3762... 

Matijevic and Wilhelmy (I) prepared uniform spherical polycrystalline particles of cadmium sulfide (CdS) by reaction of Cd2+ ions with thioacetamide (TAA) in a dilute acidic media (pH < 2), as shown in the TEM and SEM images of Figure... 

Cadmium sulfide suspensions are characterized by an absorption spectrum in the visible range. In the case of small particles, a quantum size effect (28-37) is observed due to the perturbation of the electronic structure of the semiconductor with the change in the particle size. For the CdS semiconductor, as the diameter of the particles approaches the excitonic diameter, its electronic properties start to change (28,33,34). This gives a widening of the forbidden band and therefore a blue shift in the absorption threshold as the size decreases. This phenomenon occurs as the cristallite size is comparable or below the excitonic diameter of 50-60 A (34). In a first approximation, a simple electron hole in a box model can quantify this blue shift with the size variation (28,34,37). Thus the absorption threshold is directly related to the average size of the particles in solution. 

In the presence of an excess of sulfide ion, [Cd2+ /[S2-] = 5, and in the absence of any protecting agent such as HMP, the absorption threshold of the cadmium sulfide particles reaches that of the particles obtained in aqueous solution (41) (490 nm) and the presence of HMP makes it possible to obtain smaller particle sizes (absorption threshold of the order of 470 nm). 

The fluorescence of cadmium sulfide is strongly dependent on the particle size and the presence or absence of sulfide vacancies (57,58). The fluorescence of cadmium sulfide particles observed in solution in water (37,59,60) and in acetonitrile solution (59) is dependent on the particle method of preparation of CdS particles ... 

Cadmium red consists of cadmium sulfoselenide [12656-57-4], [58339-34-7], Cd(S,Se), and is formed when sulfur is replaced by selenium in the cadmium sulfide lattice. With increasing selenium content, the color changes to orange, red, and finally dark red. The density of these pigments increases correspondingly from 4.6 to 5.6 g/cm3 and the refractive index from 2.5 to 2.8. The crystals have cubic or spheroidal habits, the prevalent particle size is 0.3-0.4 pm. 

The actions of photoexcited semiconductor particles on organic compounds under oxygen is of significant importance from both practical and basic aspects. Semiconductors like titanium dioxide and cadmium sulfide were shown to induce oxidation of olefins and aromatic hydrocarbons under oxygen, and also to sensitize isomerization of unsaturated systems. The mechanisms of these reactions are discussed. 

The approach described later on in this chapter builds upon a report in 2002, in which we proposed microfluidic reactors as favourable systems for nanoparticle synthesis, and showed that nanocrystalline cadmium sulfide prepared in such reactors exhibited improved monodispersity compared with particles prepared in conventional bulk-scale vessels (Edel et al., 2002). 

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],... 

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. 

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. 

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