Sulfide membrane

Other useful solid-state electrodes are based on silver compounds (particularly silver sulfide). Silver sulfide is an ionic conductor, in which silver ions are the mobile ions. Mixed pellets containing Ag2S-AgX (where X = Cl, Br, I, SCN) have been successfiilly used for the determination of one of these particular anions. The behavior of these electrodes is determined primarily by the solubility products involved. The relative solubility products of various ions with Ag+ thus dictate the selectivity (i.e., kt] = KSp(Agf)/KSP(Aw)). Consequently, the iodide electrode (membrane of Ag2S/AgI) displays high selectivity over Br- and Cl-. In contrast, die chloride electrode suffers from severe interference from Br- and I-. Similarly, mixtures of silver sulfide with CdS, CuS, or PbS provide membranes that are responsive to Cd2+, Cu2+, or Pb2+, respectively. A limitation of these mixed-salt electrodes is tiiat the solubility of die second salt must be much larger than that of silver sulfide. A silver sulfide membrane by itself responds to either S2- or Ag+ ions, down to die 10-8M level. 

The diffusion barrier. Much attention has been directed toward primitive amphiphile vesicles, inasmuch as they self-assemble from simple components and have an obvious ancestral connection with the more complex membranes that enclose modem cells. A review has been provided by Monnard and Deamer.55 The papers by Segre et al. and Hanczyc et al. contain additional discussion.56 57 Other prominent alternatives that would limit loss by diffusion have been electrostatic forces at mineral surfaces,58 iron sulfide membranes,59 and aerosols at the ocean-atmosphere interface.60 Section 2.7.1 discusses the function of compartmentalization in Earth life today. 

Russell, M.J., Daniel, R.M., Hall, A.J., and Sherringham, J.A. 1994. A hydrothermically precipitated catalytic iron sulfide membrane as a first step toward life. J. Mol. Evol. 39 231-243. 

Typical response curves of metal sulfide membrane electrodes in pure aqueous solutions show a linear relation with log C, with the slope expected from the Nemst... 

It is possible that inorganic cell prototypes were created in hydrothermal systems. Iron sulfides are abundant in oceanic hydrothermal systems and are one of the main products of high-temperature vents. Russell and Hall (1997) and Martin and Russell (2003) proposed that iron monosulfide bubbles, created in an oceanic hydrothermal setting formed a template for the structure of the first cells. In this model the FeS membrane acted as a catalytic chamber within which organic synthesis could take place. As this process evolved, the sulfide membrane became coated with abiotic organic polymers which eventually took over from the sulfide and replaced their function. 

If a membrane is manufactured so as to be already in equilibrium with the gas to be treated, it will not have to undergo the stresses inherent in the density changes associated with sulfiding a carbonate membrane or carbonating a sulfide membrane. While techniques for manufacturing such a membrane are still imder study, the concept has been successfiiUy used in both the coal gasification process cell d and the natural gas process cell ... 

Membranes constructed either from silverasulfide or from a mixture of silver sulfide and anollicf silver salt are useful for the determination of both. sulfide and silver ions. Toward silver Ions, the electrical response i.s similar to a metal electrode of the first kind (although the mechanism of activity is totally different). I he electrical response of a. silver sulfide membrane lo sulfide ions is similar to that of an electrode of the second kind (Section 23B-2). When the membrane is immersed in the analyte solution, a minuscule amount of silver sultlde di.ssolves and quickly saturates the tilm of liquid adjacent to the clecircxle. I he solubility, and thus the silver ion concentration, however, depends on the sulfide concentration of ihe analyte. 

The fundamental problem of a reference potential when solid contact is applied has been discussed in seminal papers. Initially, thermodynamic criteria of stability for solid-state sparingly soluble sulfide membranes were presented [5, 6], while other authors showed the application of mixed conductor AgF as a solid contact for an ionically conducting LaFs solid-state ISE membrane [7, 8]. Different contacts for ion-selective electrodes with glass membrane were reviewed by Nikolskii and Materova [9]. 

Adsorption systems employing molecular sieves are available for feed gases having low acid gas concentrations. Another option is based on the use of polymeric, semipermeable membranes which rely on the higher solubiHties and diffusion rates of carbon dioxide and hydrogen sulfide in the polymeric material relative to methane for membrane selectivity and separation of the various constituents. Membrane units have been designed that are effective at small and medium flow rates for the bulk removal of carbon dioxide. 

PPS dust should be treated as a nuisance particulate. The OSHA permissible exposure limit for respirable dust is 5 mg/m for dust containing no asbestos and less than 1% siUca. The principal decomposition products released during mol ding of PPS and their permissible exposure limits are given in Table 10. Sulfur dioxide and carbonyl sulfide are the most significant off-gases for production of mucous membrane irritation. 

The relative toxicities of thallium compounds depend on their solubHities and valence states. Soluble univalent thallium compounds, eg, thaHous sulfate, acetate, and carbonate, are especiaHy toxic. They are rapidly and completely absorbed from the gastrointestinal tract, skin peritoneal cavity, and sites of subcutaneous and intramuscular injection. Tb allium is also rapidly absorbed from the mucous membranes of the respiratory tract, mouth, and lungs foHowing inhalation of soluble thallium salts. Insoluble compounds, eg, thaHous sulfide and iodide, are poorly absorbed by any route and are less toxic. 

Ion-selective electrodes can also become sensors (qv) for gases such as carbon dioxide (qv), ammonia (qv), and hydrogen sulfide by isolating the gas in buffered solutions protected from the sample atmosphere by gas-permeable membranes. Typically, pH glass electrodes are used, but electrodes selective to carbonate or sulfide may be more selective. 

Newer fabrics, not in common use but in development, test, and field trials, are described for higher temperature applications by Reference [50]. Application to 400°F—2100°F are potentially available using ceramic fibers Nextel 312 , laminated membrane of expanded PTFE on a substrate, polyimid fiber P-84, Ryton polyphenylene sulfide, and woven fiberglass. The heat and acid resistance of these new materials... 

Methyl coenzyme M reductase plays a key role in the production of methane in archaea. It catalyzes the reduction of methyl-coenzyme M with coenzyme B to produce methane and the heterodisulfide (Figure 3.35). The enzyme is an a2P2Y2 hexamer, embedded between two molecules of the nickel-porphinoid F jg and the reaction sequence has been delineated (Ermler et al. 1997). The heterodisulfide is reduced to the sulfides HS-CoB and HS-CoM by a reductase that has been characterized in Methanosarcina thermoph-ila, and involves low-potential hemes, [Fe4S4] clusters, and a membrane-bound metha-nophenazine that contains an isoprenoid chain linked by an ether bond to phenazine (Murakami et al. 2001). 

Most of the pollutants may be effectively removed by precipitation of metal hydroxides or carbonates using a reaction with lime, sodium hydroxide, or sodium carbonate. For some, improved removals are provided by the use of sodium sulfide or ferrous sulfide to precipitate the pollutants as sulfide compounds with very low solubilities. After soluble metals are precipitated as insoluble floes, one of the water-solid separators (such as dissolved air flotation, sedimentation, centrifugation, membrane filtration, and so on) can be used for floes removal.911 The effectiveness of pollutant removal by several different precipitation methods is summarized in Tables 5.15-5.17. 

In addition to these three treatments, there are several alternative treatment technologies applicable to the treatment of common metals wastes. These technologies include electrolytic recovery, electrodialysis, reverse osmosis, peat adsorption, insoluble starch xanthate treatment, sulfide precipitation, flotation, and membrane filtration.1516... 

Robinson AV. 1982. Effect of in vitro exposure to hydrogen sulfide on rabbit alveolar macrophages cultured on gas-permeable membranes. Environ Res 27 491-500. 

Ronk R, White MK. 1985. Hydrogen sulfide and the probabilities of inhalation through a tympanic membrane defect. J Occup Med 27 337-340. 

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