Organic substances adsorption studies

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... 

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. 

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... 

Our conclusions concerning the use of the EQCM to study submonolayer or monolayer adsorption of organic substances are as follows ... 

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. 

First of all, there were two centers foimded and led by Fmmkin the Department of Electrochemistry of Fomonosov Moscow State University (MGU) and the Institute of Electrochemistry of the USSR Academy of Sciences (lEFAN). Their role was invaluable in the formation of modem theoretical concepts and also in the developments of applied electrochemistry. Organization of all aspects of EKhOS conferences, from selection of the principal theme to publication of the next volume of Progress of EKhOS, was held under the auspices of lEFAN. The Electrochemistry Department of the MGU published a textbook [21] focused on adsorption of organic substances on electrodes—an issue previously not addressed in any textbooks. Important contributions to the study of the adsorption of organic compoimds on the electrode were made by G.A. Tedoradze, A.B. Ershler, F.G. Feoktistov, and M.M. GoTdin, all at lEFAN (see G.A. Tedoradze [13], p. 23). 

While considering trends in further investigations, one has to pay special attention to the effect of electroreflection. So far, this effect has been used to obtain information on the structure of the near-the-surface region of a semiconductor, but the electroreflection method makes it possible, in principle, to study electrode reactions, adsorption, and the properties of thin surface layers. Let us note in this respect an important role of objects with semiconducting properties for electrochemistry and photoelectrochemistry as a whole. Here we mean oxide and other films, polylayers of adsorbed organic substances, and other materials on the surface of metallic electrodes. Anomalies in the electrochemical behavior of such systems are frequently explained by their semiconductor nature. Yet, there is a barrier between electrochemistry and photoelectrochemistry of crystalline semiconductors with electronic conductivity, on the one hand, and electrochemistry of oxide films, which usually are amorphous and have appreciable ionic conductivity, on the other hand. To overcome this barrier is the task of further investigations. 

Another significant application of GC is in the area of the preparation of pure substances or narrow fractions as standards for further investigations. GC also is utilized on an industrial scale for process monitoring. In adsorption studies, it can be used to determine specific surface areas (30,31). A novel use is its utilization to carry out elemental analyses of organic components (32). Distillation curves may also be plotted from gas chromatographic data. 

Wang et al. [607] studied the adsorption of dissolved organics from industrial effluents onto a commercial activated carbon. As illustrated in Table 20, they place emphasis on the pK, pK, or isoelectric point of the adsorbate and state that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. Based on their own work and analysis of the literature, they postulate that maximum adsorption of organic acids and bases occurs around their respective pK , or pKh value, even though they acknowledge, at least as the ionic organic compounds become more complex, that electrostatic adsorption forces between the adsorbent and the ionic adsorbate appear to govern. ... 

Humic substances, although a major fraction of soil DOM, do not facili- ate oxide dissolution in laboratory studies. The mobilization of metals in soils mav, however, be indirectly affected by humic substances. Solubilization of -metals may be inhibited by competitive adsorption of humic substances and LMW organic ligands. The opposite effect—an enhancement of metal morn ility—might result from the stabilization of dissolved metals as humate -omplexes. 

The majority of adsorption studies deal with the interactions between metal ions and either real or model sediment phases. Amorphous FeCOH), hydrous MnO.. clays (bentonite, illite, kaolinite), SiO., Al Oj and organic matter (often humic substances) are the solid phases most frequently studied. 

The fact that organic matter in natural and polluted water contains a complex mixture of different naturally occurring substances and pollutants, most of them at very low concentrations, represents an important reason for the adsorption study of mixtures. These can be done at natural and model phase boundaries. Selected well-defined and easily controlled model interfaces have some advantages for the study of very complex systems such as adsorbable organic matter in natural waters. 

Because of its nonpolar and hydrophobic character, the mercury-water may serve as a good model interface for the adsorption study and determination of the organic substances that are adsorbed primarily because of hydrophobic expulsion. There is generally a proportionality of adsorbability (free energy of adsorption) found at the mercury electrode to a number of -CH2 groups in paraffinic hydrocarbon residues in nonpolar surfactants and a similar relation between the octanol water partition coefficient and chain length. This was recently also illustrated in the case of adsorption of aliphatic fatty acids (Ulrich ct al., 1988). 

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