Cadmium sulfide ions

The commonly accepted underlying mechanism involves decomposition (hydrolysis) of thiourea in the alkaline solution to form sulfide ions (3.10), which react with Cd " ions released by the decomplexation reaction (3.11), with precipitation of cadmium sulfide (3.12) upon exceeding the solubility product of the compound... 

Changing the substrate from gold to silver has been shown to strongly affect the structure of the first few layers of CdS grown by ECALE. STM measurements carried out on the first CdS layer on Ag(lll) revealed a much less compact structure than the one found on Au(lll). This disparity was tentatively attributed to the different structure of the first S layer on Ag(l 11), as obtained by oxidative UPD from sulfide ion solutions, due to a higher affinity of sulfur for silver than for gold. The Cd layers were attained on S by reductive UPD from cadmium ion solutions. Precursors for both elements were dissolved in pyrophosphate/NaOH at pH 12 [43 5],... 

Nakatani K, Matsudaiva S, Tsubomura H (1978) Photoanodic behavior of n-type cadmium sulfide in acetonitrile solutions containing iodide ion. J Electrochem Soc 125 406 09... 

Fujishima A, Sugiyama E, Honda K (1971) Photosensitized electrolytic oxidation of iodide ions on cadmium sulfide single crystal electrode. Bull Chem Soc Japan 44 304 Inoue T, Watanabe T, Fujishima A, Honda K, Kohayakawa K (1977) Suppression of surface dissolution of CdS photoanode by reducing agents. J Electrochem Soc 124 719-722 Elhs AB, Kaiser SW, Wrighton MS (1976) Visible light to electrical energy conversion. Stable cadmium sulfide and cadmium selenide photoelectrodes in aqueous electrolytes. J Am Chem Soc 98 1635-1637... 

Ginley DS, Butler MA (1978) Flatband potential of cadmium sulfide (CdS) photoanodes and its dependence on surface ion effects. J Electrochem Soc 125 1968-1974... 

Mau AWH, Huang CB, Kakuta N, Bard AJ, Campion A, Eox MA, White JM, Webber SE (1984) Hydrogen photoproduction by Nafion/cadmium sulfide/platinum films in water/sulfide ion solutions. J Am Chem Soc 106 6537-6542... 

Figure 29.4 shows an example, the energy diagram of a cell where n-type cadmium sulfide CdS is used as a photoanode, a metal that is corrosion resistant and catalytically active is used as the (dark) cathode, and an alkaline solution with S and S2 ions between which the redox equilibrium S + 2e 2S exists is used as the electrolyte. In this system, equilibrium is practically established, not only at the metal-solution interface but also at the semiconductor-solution interface. Hence, in the dark, the electrochemical potentials of the electrons in all three phases are identical. 

The ion that determines the p>otential of the compact layer is called the potential-determining ion. In cases in which the potentied of compact layer is determined by the dissociation reaction of adsorbed hydroxyl groups, the potential -determining ions are hydrated protons or hydroxide ions. For cadmium sulfide electrodes, the potential-determining ions are not hydrated protons but hydrated sulfide ions the iso-electric point is at the sulfide ion concentration of 4 x 10 M [Ginley-Butler, 1978]. 

Fujishima A, Sugiyama E, Honda K (1971) Photosensitized electrolytic oxidation of iodide ion on cadmium sulfide single crystal electrode. Bull Chem Soc Jpn 44 304... 

The manufactnring process for the important zinc and cadmium sulfide phosphors involves precipitation of the sulfide from purified salt solutions, e.g. the snlfate, with hydrogen snlfide. For ZnS Cu, the copper activator is added, as a readily decomposed derivative, to the sulfides and after grinding the components are fired in fnmaces at temperatures in the range 800-1200 °C. ZnS Ag, the bine phosphor nsed in CRTs, is prepared by firing zinc sulfide with silver nitrate at 1000 °C, nsnally in the presence of sodinm chloride to give the co-activating chloride ions. 

The Cd/CdS electrode was also prepared in solutions containing cadmium sulfate and sodium thiosulfate using the potentiodynamic method [183]. The electrochemical behavior of such electrodes in electrolytes containing sulfide ions was studied. 

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... 

In aqueous solution, the mixture of solutions containing cadmium and sulfide ions induces a precipitation of CdS semiconductor. When adding a protecting polymer such as sodium hexainetaphosphate (HMP) in the solution, no precipitation is observed and a yellow solution remains optically clear, indicating the formation of CdS clusters. In reverse micelles, similar behavior of the latter is observed, as shown later. 

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). 

In the presence of an excess of sulfide ions, [Cd2+]/[S2 ] = 5, a strong change in the absorption spectra at low water content is observed compared to that obtained for a ratio of [Cd2+]/[S2-] equal to 2. By increasing the water content, the sharp peak disappears and a similar behavior as in the case of excess of cadmium is observed, i.e., a red shift in the absorption spectrum. The sharp peak observed at low water content increases with the relative amount of sulfide ions (45). This peak is attributed to sulfide clusters (55) formed on the CdS particles because of the high local concentration of sulfide ions. The disappearance of this peak when increasing the water content could be explained by the fact that sulfide clusters, with negative charges, are repelled to the center of the droplets and redissolve themselves inside the water pool. 

The average radius is deduced. Figure 3.4.2 shows a change in the size of the particle with the molar ratio of cadmium and sulfide ions concentrations. The largest size particles are obtained for [Cd2+]/[S2-] = 1 and the smallest for [Cd2+]/[S2 ] = 2. It can be noticed that the size of CdS is always smaller when one of the two reactants are in excess ([Cd2+]/[S2 ] = 3,5, 2). This confirms that the crystallisation process is faster when one of the reacting species is in excess (56). 

In the presence of an excess of sulfide ions two fluorescence emissions are observed. The first is centered at 450 nm and is attributed to the direct recombination of charge carriers. The second emission band, observed at around 650 nm, depends on the particle size. This second emission band is very weak and is very often quenched by the presence of species absorbed at the interface. By analogy it could be attributed to cadmium ion vacancies. 

The addition of macrocycles on CdS synthesis in reverse micelles induces a strong change in absorption spectra. For a given water content, a red shift of absorption onset is observed in presence of macrocycles. This effect is more pronounced in presence of Kryptofix 222 and when the CdS nanocrystallite synthesis is realized in presence of an excess of sulfide S2 ions (x = ). This red shift is characteristic of an increase in the average nanocrystallite size. It can be noticed that absorption of CdS particles synthetized in reverse micelles in presence of an excess of cadmium Cd2+ ions (x = 2) is reduced in presence of macrocycles. This indicates a decrease in the yield of CdS particles and is attributed to complexation of functionalized... 

Sol-gel techniques can be used to produce thin layers, as described in Section 19.1. For example, cadmium sulfide layers for photocells are easily made by spraying an ammoniacal solution of cadmium chloride and thiourea (which hydrolyzes to give sulfide ion) onto a substrate surface and baking the resulting CdS film at up to 500 °C ... 

Pure cadmium selenide [1306-24-7], CdSe, is brownish black and has no pigment properties. Like cadmium sulfide, it is dimorphous and occurs in hexagonal and cubic modifications. Cadmium selenide is insoluble in dilute acid. It readily liberates hydrogen selenide in concentrated hydrochloric acid. It dissolves completely in fuming nitric acid, the Se2 - ions being converted to SeO2 ions. Cadmium selenide is an n-type semiconductor. 

Cation holes can also be created by coactivation with trivalent metal ions or by incorporation of oxygen [5.313]. The luminescence band of self-activated zinc sulfide with the zinc-blende structure exhibits a maximum at 470 nm. On transition to the wurtzite structure, the maximum shifts to shorter wavelengths. In the mixed crystals zinc sulfide-cadmium sulfide and zinc sulfide-zinc selenide, the maximum shifts to longer wavelengths with increasing cadmium or selenium concentration. 

It is known that cadmium sulfide (CdS) and ion oxide Te203) are visible light-sensitive materials, in particular, one-step photocata ysis of wate - is possible for CdS.25) Recently, Kudc et at. reported that bismuth vanadate (BiV04) snowed photocatalytic activity for 02 evolution from an aqueous silver nitrate solution under visible light.26 271 BiVCX is a very attractive photocatalyst although it is impossible to decompose water by a one-step process. Thus this material is a candidate for an 02 evolution photocatalyst to construct a two-phoion process 26) In other words, this material is expected to be an 02 evolution photocatalyst to... 

One interpretation presumes that the photocurrent onset in the absence of sulfide is determined by electron-hole recombination. The sulfide ions on the surface are then supposed to be bound to these surface recombination levels rendering them unavilable for recombination reactions. The charge transfer reactions could then proceed at lower voltages. In this case the corrosion suppression role of the sulfide ions would be to reduce the oxidized corrosion site before a cadmium ion could go into solution. A variation on this theme is to consider the corrosion site to be the recombination state, i.e., the site on the surface that normally leads to corrosion when oxidized by a photoexcited hole can be... 

For the case when the cadmium salt, sulfide ion and complexing agent L are the initial compounds for colloid formation, the following set of equations is valid ... 

Therefore, the suggested equation (2.19) reflects adequately a variation in the properties of luminescence quenchers and describes well the experimental data as a whole. In addition, the data suggest that for the colloids obtained with an excess of the sulfide ions, the quencher adsorption site is represented most likely by the negatively charged surface sulfur atoms, on which the cations adsorb readily while the anions adsorb poorly. Actually, in this case, the dominant surface defects are either the vacancies of the cadmium ions, or... 

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... 

Aside from these three classes (species with unfilled inner subshells, with unpaired electrons, or with two different oxidation states of the same element), there are a number of colored inorganic substances about which generalizations may be set up only with difficulty. Among these are many of the elementary nonmetals, a large number of covalent salts (such as mercuric iodide, cadmium sulfide, silver phosphate and lithium nitride), a number of nonmetal halides (iodine monochloride, selenium tetrachloride, antimony tri-iodide, etc.), and the colored ions, chromate, permanganate, and Ce(H20) v, whose central atoms presumably have rare-gas structures. 

Photosensitized Electrolytic Oxidation of Iodide Ions on Cadmium Sulfide Single Crystal Electrode. The stability of CdS probe under irradiation in an electrolyte containing iodide species. Rotating ring disk voltammetry was used as the methodology. 487... 

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