Adsorption of organic substances

Renewed Sn + Cd alloy surfaces have been studied by Safonov and Choba821 by impedance. The has been found to shift toward more negative E with time, suggesting that the content of Cd at the Sn + Cd alloy surface increases with time. For the alloy with 10% Cd, the time dependence of C for adsorption of organic substances is significantly different from that for Sn + Pb alloys. At relatively short times, E"1 shifts in the negative direction, which shows the increase of the Cd content in the Sn + Cd alloy surface layer. At longer times, an additional adsorption-desorption peak (step) has been observed, which has been explained by the formation of rather wide two-dimensional areas of Cd microcrystals at the alloy surface.824... 

Figure 26. Plot of the Gibbs energy of adsorption of organic substances at a = 0 vs. the interfacial parameter, AX. (1) 1-Hexanol, (2) 1-pentanol, and (3) acetonitrile. From Ref. 32, updated. Additional points (1) Au(l 11),910 Bi(l 11),152 and (2) Ga916...

FIGURE 10.8 Influence of the adsorption of organic substances (a) on the electrocapillary curve, (b) on the capacitance curve, and (c) on the plot of surface charge against potential (1) 0.1 M H2SO4 solution (2) the same, with 0.1 MC4H9OH. 

Damaskin, B.B.andFrumkffiA. N. (1974) Potentials of zero charge, interaction of metals with water and adsorption of organic substances—111. The role of the water dipoles in the structure of the dense part of the electric double layer. Electrochim. Acta, 19, 173-176. 

The quasi-reversihle electroreduction processes of Zn(II) in the absence and in the presence of Ai,Ai -dimethylthiourea (DMTU) were quantitatively compared by Sanecld [91], It has been shown that in the presence of DMTU enhanced response of cyclic voltammetry and normal pulse polarography was complex and could be resolved into its regular reduction part and a part caused by the catalytic influence of adsorption of organic substance. 

Fig 6.115. Gibbs energy change for adsorption of organic substances on different crystal faces of various metals, as a function of the corresponding potential of zero charge cyclohexanol (1), camphor (2), cyclohexanol (3), diethylether (4), and cyclohexanol (5). (Reprinted from S. Trasatti, Russ. J. Electrochem. 31 713, 1995, Fig. 7.)... 

Before adsorption of organic substances the adsorbents were placed into a measuring ampule 4 mm in diameter that was connected to a glass vacuum installation. Then the adsorbents were subjected to a thermal vacuum treatment at 500 K and 1 Pa for 3 h. following which the adsorbents were equilibrated with saturated vapours of organic substances at 293 K for 2 h (in the case of methane the adsorbate pressure in the system was equal to atmospheric pressure). When the adsorption process was completed, the ampules were sealed without contact with air and placed into the measuring element of the NMR spectrometer. 

Studies involving the adsorption of organic substances onto solid phases have largely centered around organic pesticides because of the environmental significance of these toxic substances. The extent of adsorption of Bromacil onto freshwater... 

Adsorption of Organic Substances at the Mercury Electrode-Solution Interface... 

Cosovic, B., and M. Branica (1973), Study of the Adsorption of Organic Substances at a Mercury Electrode by the Kalousek Technique, J. Electroanal. Chem. 46, 63-69. 

Figure 9. Plots of 0 vs.. cj (o o o and —) and (AG a)/RT vs., ( and —) due to ethylene glycol adsorption on a Hg electrode at concentrations 2, 1.6, 1.2, 1.0, 0.7, 0,5 and 0.2 mol dm (from top to bottom). Points are experimental data reprinted from J. Electroanal. them., 28, S, Trasatti, Effect of the Nature of the Supporting Electrolyte on the Thermodynamic Analysis of the Adsorption of Organic Substances on Mercury. Adsorption of Ethylene Glycol form 0.1 m Aqueous Solutions of Halides, p. 257, Copyright 1970, with permission from Elsevier Science. Curves were calculated from Eqs. (16), (21), and (23) using the parameters given in text.

An apphcation of the thermodynamic theory of Pt hydrogen electrode to the reversible adsorption of organic substances leads to a conclusion [87] that the maximum adsorption of neutral molecules should be observed in the potential region, where the adsorption of both hydrogen and oxygen is low (so[Pg.344]

Measurement of redox potentials is relatively inaccurate. As the redox potential measurements are easily influenced by adsorption of organic substances such as minute amounts of oil, it is essential to clean the electrode surface. This is best done with a mixture of calcium carbonate, detergent, and trisodium phosphate. 

A more elaborate theory of orientation effects was developed by Watts-Tobin and Mott and applied by Bockris, Devanathan, and Muller and Bockris and Habibto the calculation of isotherms for adsorption of organic substances. Solvent molecules were regarded as being present in the double layer in two orientations, up or down (cf. theories of ferromagnetism) at respective surface coverages of N or N[. The sum iVf + is equal to the total coverage of the electrode by solvent molecules. 

This relation enables the surface dipole potential d to be evaluated together with other functions for adsorption of organic substances which displace the field-oriented solvent dipoles. 

In more complex cases, e.g., isotherms with interaction terms, R/n can usually be evaluated by the method exemplified above. The results for several isotherms that have been investigated for adsorption of organic substances at electrodes are summarized in Table 2. 

Although the Faradaic process is frequently the primary subject of ac polarographic experiments, the simultaneous study of the capacity of the double layer which the method allows has provided valuable information upon the influence of adsorption of organic substances upon this capacity and... 

A. N. Frumkin and V. I. Melik-Gaykazyan [1951] Determination of the Kinetics of Adsorption of Organic Substances by a.-c. Measurements of the Capacity and the Conductivity at the Boundary Electrode-Solution, Dokl. Acad. Nauk 77, 855-858. 

Once the mass of replaced water molecules has been taken into account (or it was assumed a priori that this was negligible), the response of the EQCM can be used to compare surface excess Fa, obtained from the frequency shift with that derived from other techniques. However, the situation is complicated by the fact that the absolute value of the frequency shift caused by adsorption of organic substances is usually small, similar to that caused by electrostatic adsorption of ions in the diffuse double layer over the same range of potential, as seen, for example, in Fig. 9. Thus, the effect of the diffuse double layer must be considered as a background, and a suitable correction should be made. 

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