Oxidation potentials absorbance maxima

The interaction of PANI with dichromate is of particular interest because of possible application in waste water treatment systems [499]. Figure 52 (top) shows a UY-vis spectrum of a potassium dichromate solution. The main absorbance band is located at ca. A = 350 nm. It does not interfere with the major absorbance band of the oxidized (emeraldine) form of PANI. Figure 52 (bottom) shows spectra obtained at different time intervals after the immersion of the PANI-coated ITO glass electrode into the dichromate solution. Immediately after immersion of the PANI-coated electrode, a shift of the absorbance maximum of PANI film is observed. As compared to the spectrum of PANI obtained at Erhe = +0-8 V (spectnun A in Fig. 52 (bottom)], the absorbance maximum shifts from A = 750 nm to ca. A = 660 nm. Earlier, a comparable shift of the absorbance maximum after switching the electrode potential from rhe = +0.8 Y to RHE = +1-1 or +1-2 Y was found [509]. Consequently, the shift indicates that a redox reaction between dichromate ions and the PANI film proceeds. Because of the high value of Eq for dichromate ions foe PANI film becomes oxidized and shows the corresponding spectral features of the oxidized state found at high electrode potential values. 

Nafion film coated on an ITO electrode to understand the structural transformations of the dimer in the Nafion coating during the catalytic water oxidation process . The absorption spectral changes observed during the oxidation scan from 0.4 to 1.4 V (s. SCE) (Fig. lOA) showed a decrease in the absorbance at 655 nm with simultaneous increase in the absorbance at around 450 nm with clear isosbestic points at 430 and 545 nm. In the reductive scan from 1.4 to 0.4 V (vs. SCE) (Fig. lOB), the absorbance at 655 nm increased and a simultaneous decrease in the absorbance at 450 nm was observed with an isosbestic point at 555 nm. The absorbance at 655 nm was almost recovered back. Initially the oxidation of the dimer complex H20-Ru" -Ru "-0H2 leads to the formation of H20-Ru "-Ru -0H2 with an absorption maximum at around 450 nm and further oxidation at higher positive potentials must lead to Ru -Ru formation in a successive oxidation process. The Ru -Ru would be rapidly reduced by water molecules to produce H20-Ru -Ru -0H2 at pH 1. The same in situ spectrocyclic voltammetry experiments at pH 9.3 showed an absorption maximum at around 500 nm with the formation of H20-Ru" -Ru -OH in the Nafion film. In relevant to the absorbances at 450... 

Multilayer Lay-Up Prior to Lamination. In addition to the oxide and oxide alternative processing discussed in the previons section, the hold time between this process and multilayer lay-up and lamination is also important.This is due not only to the possibihty of oxidation of the innerlayer surfaces, but to the potential for moistnre absorption by the exposed resin surfaces on the innerlayer, for the reasons already discnssed. This hold time should be minimized, and the storage of the innerlayers prior to lay-np shonld be in a temperature- and hnmidity-controUed environment to rednce the likelihood of absorbing moisture. Typical environmental conditions for this storage are 68°F or 20°C, and a maximum of 50 percent relative hnmidity (RH), although lower humidity levels are recommended. 

A = absorbance b = path length e = electron E = electrode potential = reversible electrode potential p = peak potential E = anodic peak potential p, = cathodic peak potential = Faraday constant (96 485 C mol" ) k = rate constant eq - equilibrium constant n = number of electrons O = oxidized form R = reduced form R - gas constant (8.315 J K i mol ) t = time T = temperature in kelvin f = molar extinction coefficient = wavelength of maximum absorbance. 

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