Colloid metal sulfides

Weller, H., Koch, U., Gutierrez, M. and Henglein, A. (1984). Photochemistry of colloidal metal sulfides. 7. Absorption and fluorescence of extremely small ZnS particles (the world of the neglected dimensions). Ber. Bunsenges. Phys. Chem. 88, 649. 

Weller H, Koch U, Gutierrez M, Henglein A (1984) Photochemistry of Colloidal Metal Sulfides, 7. Absorption and Fluorescence of Extremely Small Zns Particles -the World of the Neglected Dimensions. Ber Bimsenges 88 649-656... 

Adsorption is the principal source of contamination of precipitates that have large surfaces, for example, flocculated colloids (metal sulfides, silver halides, hydrous oxides). The extent of adsorption may be relatively small, as it usually is with silver halides, or severe, as it often is with hydrous oxides. 

Henglein A, Gutierrez M, Fischer CH Photochemistry of colloidal metal sulfides. 6. Kinetics of interfacial reactions at ZnS particles. Berichte Der Bunsen-Gesellschaft-Physical Chemistry Chemical Physics 1984, 88(2) 170-175. 

Alfassi Z, Bahnemann D, Henglein A Photochemistry of colloidal metal sulfides. 3. Photoelectron emission from CdS and CdS-ZnS co-colloids. J Phys... 

Henglein A, Gutierrez M Photochemistry of colloidal metal sulfides 5. Fluorescence and chemical reactions of ZnS and ZnS/CdS co-colloids. Berichte Der Bunsen-GeseUschaft-Physical Chemistry Chemical Physics 1983, 87(10) 852— 858. 

The aqueous decomposition of thiourea to sulfide and cyanamide has been found to be catalyzed by metal hydroxide species and colloidal metal hydroxide precipitates. Kitaev suggested that Cd(OH)2 is actually required for CdS film formation to occur by adsorption of thiourea on the metal hydroxide particles, followed by decomposition of the Cd(OH)2-thiourea complex to CdS. Kaur et al. [241] found... 

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. 

Photoreduction of CO2 to formate in metal sulfide colloids has been reported to provide a novel photosynthetic route for production of methanol as the end-product... 

When colloids of metal sulfides, selenides, phosphides and arsenides are illxuninated in the presence of air, decomposition takes place. Metal ions migrate into solution and sulfate, selenite, phosphate or arsenate are formed. The process was first investigated in the case of colloidal CdS... 

The technique of alternating polyelectrolyte film construction has also been adapted to incorporate semiconductors into layered films. For example, multilayer films have been constructed by alternately dipping a quartz substrate into a solution of poly(diallylmethylammonium chloride) and then a solution of a stabilized CdS or PbS colloid (41). The layer-by-layer self-assembly of alternating polymer and metal sulfide is at least partially driven by the electrostatic attraction of the cationic polymer and the negative charge of the stabilized MC colloid particles. 

Flosdorf and Chambers (1933) reported that metal sulfides were oxidized in the presence of audible sound (1 to 15 kHz) while investigating the bactericidal action of audible sound however, Schmitt et al. (1929) were the first researchers to observe the rapid oxidation of dissolved H2S gas to colloidal sulfur during sonication at 750 kHz with a 250-W power source. They reported that an increase in the total pressure of the system (P02) led to higher oxidation rates up to a limiting critical pressure. This critical pressure depended on the amount of dissolved H2S gas and the intensity of irradiation. The primary oxidation product was found to be elemental sulfur. The overall reaction was thought to proceed via reactions of HS with OH radicals, HO radicals, or H202. 

In the second method, a metal salt solution (silver, lead, or bismuth less often nickel, cobalt, or manganese) is applied colloidal sulfur may also be added. Dyeing is based on (1) The reaction of the metal salts with the added sulfur and the sulfur in the hair keratin, which yields metal sulfides, and (2) The deposition of finely divided metals or metal oxides. With these products progressive coloration also is obtained. 

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],... 

Charge transfer reactions have mainly been studied with regard to colloidal particles of Ti02, and to some extent with regard to metal sulfides such as CdS. Illumination of CdS colloids in aqueous solutions saturated with oxygen, have led to a relatively fast anodic corrosion according to the reaction [38]... 

Sun, Z.-X. et al.. Surface reactions in aqueous metal sulfide systems. 3. Ion exchange and acid/base properties of hydrous lead sulfide. Colloids Surf., 59, 243, 1991. 

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