Heterogeneous solid-state membrane

Since they operate in the same fashion, the electric and electrochemical properties of the heterogeneous solid-state membrane electrodes on the market today resemble those of the homogeneous precipitate membrane electrodes in many ways. The most important data are summarized in Table 3. By the same principles outlined in the previous chapter, the heterogeneous iodide electrode can also detect cyanide. In contrast to the homogeneous membranes, those which include silicone rubber as a support ma-... 

Table 3. Heterogeneous solid-state membrane electrodes... 

The commercially available heterogeneous solid-state membrane electrodes should be conditioned in a 0.1 M solution of the ion to be measured for about 2 hours before the first measurement. With self-made electrodes having materials which are not ion-conductors, a conditioning in a 1 M measured ion solution at 90°C is recommended. Drying out of the active phase is to be avoided, since the accompanying shrinkage can cause fine cracks in the membrane. Such electrodes are best handled like glass membrane electrodes, and stored in a 0.01 to 0.1 M solution of the indicated ion between measurements. 

Other types of solid-state membranes include single crystals of sparsely soluble salts and are often called heterogeneous membranes, in which the insoluble salt is embedded in some inert polymer matrix. Obviously, in order for these membranes to be at equilibrium they should be in a saturated solution. In practice, these membranes are used in solutions that are below saturation. In that case, the insoluble salt slowly dissolves. 

Several quite different types of membranes have been used in the construction of ion-selective electrodes, namely (1) glasses (2) solid-state membranes (3) heterogeneous membranes and (4) liquid membranes. 

In aqueous systems, membrane lipids may exist in a gel-like solid state or as a two-dimensional liquid. In the case of pure phospholipids, these states interconvert at a well-defined transition temperature, Tc, that increases with alkyl chain length and decreases with introduction of alkyl chain unsaturation. In cell membranes, which have marked heterogeneity in both the polar and nonpolar domains of the bilayer, this state is described as liquid disordered . The presence of sufficient sphingolipids, with... 

Heterogeneous membrane Similar to solid-state type but active material dispersed in inert matrix. Cf, Br, I, S2, Ag+... 

Incorporation of Biocatalysts Into Synthetic Membranes. It Is generally accepted that only a few enzymes exist In vivo as a free protein In an aqueous medium, and that most of them either are bound to membranes or to solid-state assemblies or are present In a gel-llke surrounding. Enzymes attached to synthetic membrane matrices may serve as specific heterogeneous catalysts that can be used repeatedly. If they are sufficiently stable. In comparison to natural membranes, enzyme-bound synthetic membranes possess the advantage that they are mechanically more stable. 

Solid-state electrochemistry is an important and rapidly developing scientific field that integrates many aspects of classical electrochemical science and engineering, materials science, solid-state chemistry and physics, heterogeneous catalysis, and other areas of physical chemistry. This field comprises - but is not limited to - the electrochemistry of solid materials, the thermodynamics and kinetics of electrochemical reactions involving at least one solid phase, and also the transport of ions and electrons in solids and interactions between solid, liquid and/or gaseous phases, whenever these processes are essentially determined by the properties of solids and are relevant to the electrochemical reactions. The range of applications includes many types of batteries and fuel cells, a variety of sensors and analytical appliances, electrochemical pumps and compressors, ceramic membranes with ionic or mixed ionic-electronic conductivity, solid-state electrolyzers and electrocatalytic reactors, the synthesis of new materials with improved properties and corrosion protection, supercapacitors, and electrochromic and memory devices. 

Figure 2 Basic types of ISE (A) glass electrode (B) electrode with a solid homogeneous or heterogeneous membrane (C) classical liquid membrane electrode (D) electrode without internal solution (all-solid-state electrode) (E) coated-wire electrode. 1, Internal standard solution 2, internal reference electrode (Ag/AgCI) 3, membrane 4, glass or plastic body of the electrode 5, reservoir of the electroactive substance solution 6, solid-state contact and 7, metal wire.

In addition to the oxygen separation membranes, the proton conducting membranes can also be applied to reduce NO emission by combining heterogeneous catalysis and solid state electrochemistry. The solid electrolytes in MRs serve to electrochemically control chemisorptive bonds and enhance catalytic activity. Figure 8.10 shows the schematic diagram of a steam electrolysis cell constructed with a proton conductor for reducing NO. Steam is electrolyzed at the anode. It shows the produced H+ is electrochemically pumped to the cathode and reacts with NO to produce Nj and HjO ... 

Figure 3-2 shows the cellular membrane microstructure of a P-quartz solid solution glass-ceramic. The individual phases are presented in connection with their effect on the different solid-state reactions to provide a better understanding of this microstructure. As described in Section 2.2.2, the nucleation of P-quartz solid-solution crystals is heterogeneously initiated by ZrTiO nucleating agents. These ZrHO crystals represent the nucleus of the... 

Solid-state characterization techniques have been used to verify that the heterogenization procedure did not damage the catalyst. Fourier transform-infrared (FT-IR) spectra give useful indication about the structure of the catalyst heterogenized in the membrane. FT-IR spectra confirmed that the catalyst stmetore is preserved within the polymeric membrane (Fig. 27.1). The infrared spectrum of the catalytic membranes show the characteristic bands of Wio units (595, 803, 895, 958 cm ), as well as those typical of the employed alkylam-monium cation (2870 cm ). 

A Ru complex, Ru(dcbpy)3 where debpy is 4,4 -dicarboxyl-2,2 -bipyri-dine, was covalently anchored onto an insoluble Sephadex, and heterogeneous electron-transfer quenching of the excited state in the solid phase was studied in water containing or iVA -dimethylaniline [80]. The electron transfer was very efficient in polar solvents. Electron transfer of excited state Methylene Blue incorporated in a Nafion membrane by Fe has been reported [81]. The electron-transfer process involved excitation of the dye dimeric species or excimers. 

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