The Adsorption of Organic Substances

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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. 

The properties of the diffuse double layer depend directly on the surface charge density and not on the potential. In order to correct for this effect quantitatively, one needs to convert the dependence of frequency on potential A/( ), observed experimentally, to its dependence on charge density, A/( q). Having the analogous dependence A/o( q) for the supporting electrolyte, it is possible to evaluate the real response of the EQCM to specific adsorption, 5f q) = A/( ) — A ( ), and use this response for interpretation of the data obtained. This approach was taken in [74, 108,111] for several systems as seen in Figs. 9 and 10. For all cases studied, the surface excess was known from independent electrochemical experiments. 

Consider first the influence of the nature of the metal on the response of the EQCM to specific adsorption. This can manifest itself in the shapes of the resulting dependence of bf (q) on q, because of a change of the pzc 

The function bf q) can be converted back to a dependence on potential bf E). The adsorption of organic substances has been discussed in the literature either as a function of potential (usually referred to as the pzc) or as a function excess surface charge q. The question regarding which of the two should be preferred has not been entirely resolved and will not be discussed here. 

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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. 

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... 

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.

Since hematite represents some aspects of the soil behavior, the aim of this study is to apply the proposed method to this colloid, and to obtain corresponding thermodynamic parameters. In addition, some results of the adsorption of organic substances on the hematite will be discussed. 

In the 1960s, a few Soviet scientists were allowed to visit Western countries. Vladimir Yevgenievich Kazarinov worked in the Bockris Laboratory in Philadelphia. He made radiotracer studies of the adsorption of organic substances on metals. Likewise, Lev Nikolayevich Nekrasov (22 February 1931-19 March 2010) trained for a year in Cleveland in the laboratory of Ernest B. Yeager (26 September 1924— 8 March 2002). However, the majority of Soviet scientists were not permitted to work overseas. 

Except for the adsorption of metal ions, chitosan gels can be applied in the adsorption of organic substances. Novel gels from phenylboronate derivatives of chitosan were prepared for the adsorption of saccharides hy Matsumoto et al. [40]. The adsorption characteristics of D-glucose and 1-methyl-a-D-glucoside on the gels were examined and compared with a commercial gel. The resulted showed that the chitosan gels were inferior to the commercial gel in their adsorption capacity. 

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