0 Copyright 1987
American Chemical Society
The ACS Joumal of
Surfaces and Colldds MAY/JUNE, 1987 VOLUME 3, NUMBER 3
Articles A. V. Kiselev's Contributions to Adsorption Science7 Kenneth S. W. Sing Department of Chemistry, Brunel Uniuersity, Uxbridge, Middlesex LIB8 3PH, England Receiued August 12, 1986
Andrei Vladimirovich Kiselev, who died in Moscow on July 17, 1984, must surely rank as one of the leading surface scientists of our time. His research output was extraordinary: he and his co-workers produced over 900 original papers and reviews and eight books-for the most part in the space of 30 years! One might imagine that Kiselev had very little time for other activities, but in fact he had wide-ranging interests in arts and crafts. Indeed, his Moscow apartment was a stately home in miniature-crammed with antique furniture, old clocks, French porcelain, and other ohjeta d'art. Kiselev was passionately fond of ecclesiastical architecture, and it was a rewarding experience to accompany him on a visit to an ancient church or cathedral. Kiselev's career and international reputation gained momentum shortly after World War II when as professor of physical chemistry he established his Laboratory of
Adsorption (later to become Adsorption and Chromatography) in the M. V. Lomonmv State University, M m w , together with the Laboratory of Surface Science in the Institute of Physical Chemistry of the USSR Academy of Sciences. Until the time of his death these two large groups of surface scientists continued to work together happily and successfully under his inspired leadership. Porous carbons and silica gels were the most popular adsorbents to be studied by Kiselev and others in the 193Os,but in the late 1940s Kiselev was one of the first to appreciate the opportunity offered by the development of the Aerosil grades of silica (in Germany) and the graphitized carbon blacks (in the USA) to study well-defined and reproducible, nonporous adsorbents. By 1957,when he made his first visit to Britain, Kiselev had already demonstrated the importance of surface structure in the context of physical adsorption and also he and his coworkers had obtained remarkahly good agreement between their calculated heats of adsorption and the corresponding experimental values for a range of organic molecules adsorbed on the basal plane of graphite. Furthermore, the Russian scientists were probably the first to present unequivocal evidence of the effect of pore narrowing in changing the isotherm shape from type I1 to type I. One cannot overemphasize the tremendous impact of all these results and ideas when they were brought to our attention at the Second Congress of Surface Activity' in 1957. The impression received was that physical adsorption had come of age! During the 1960s Kiselev and his eo-workers extended their detailed studies of the changes in adsorptive properties brought ahout by the removal of hydroxyl groups
'This Appreciation of A. V. Kiselev is intended to serve an an appropriata introduction to the collection of papem that come from the symposium that WBS held in his honor, on the masion of the Colloid and Surface Science Symposium, Atlanta, GA, June 15-28,
(1) Kiselev, A. V. In Second Intomtiom1 C o m s s on Surface Actiuity; sehuhnan,J. H., Ed.;Buttemrtk Lendon, 1957; VoL II,pp 168,
1986.
179, 202, 204, 208, 215, 228.
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308 Langmuir, Vol. 3, No. 3, 1987
from the surface of nonporous silica. These effects provided a basis for the concept of the specificity of physisorption*and the related classification of adsorbents and adsorbate^.^ By the end of the decade the broad picture seemed clear, but in fact any tendency toward complacency turned out to be short-lived. In the early 19709several new aspects came to light which appeared to cast doubt on Kiselev’s overall interpretation. It became evident4 in 1971 that some grades of silica Aerosil, previously regarded as pure, in fact contained small amounts of A1 and that the impurity had a marked effect on the surface properties of the dehydrated material. Thus, by the application of infrared spectroscopy it was shown that strong acid sites were produced by heat treatment of the Russian Aerosil at temperatures 1000 “C. To avoid this complication, another series of adsorption measurements was conducted5 on samples of pure silica which had been subjected to hydrothermal annealing, i.e., the so-called aerosilogel. The effect of high-temperature surface dehydroxylation of this new grade of nonporous silica was studied by adsorption calorimetry and infrared spectroscopy. The results obtained with polar adsorbates (e.g., benzene, diethyl ether, nitromethane, pyridine, and tetrahydrofuran) were qualitatively similar to those reported earlier, but it was found that nonpolar adsorbates (n-hexane, cyclohexane, and carbon tetrachloride) all exhibited much weaker interactions with the dehydroxylated silica than had been recorded previously. It was suggested5 that the polarization contribution was likely to have been considerably reduced as a result of the very low residual OH concentration. Although this explanation is questionable, the results were of considerable importance because they revealed that it was possible to produce silica having a high degree of surface uniformity (i.e., on which the differential heat of adsorption remains nearly constant over a wide range of surface coverage). In the 1960s and 19709 the attention of Kiselev and other Soviet surface chemists became increasingly focused on the adsorptive properties of molecular sieve zeolites. In the course of this work Kiselev drew attention6 to the limitations of the Dubinin-Fladushkevich and Dubinin-Astakhov equations and pointed out that a virial form of equation produced a more rigorous means of analyzing isotherm data obtained with both nonporous and microporous adsorbents. These studies led Kiselev and Poshkus7to develop their molecular statistical theory of adsorption for the Henry’s law region of the isotherm. The theoretical basis for the calculation of the Henry’s law constant, Kl, was provided by the customary treatment of the statistical distribution of adsorbate molecules at very low surface coverage. Thus
-
K1 = aj[exp(-+/kT)
- 11 dq
dw
where a is a coefficient dependent on the symmetry of the adsorbate molecule and the adsorbent, is the potential energy of interaction of the molecule with the adsorbent, and q and w represent respectively,the sets of coordinates of the center of mass and the Eulerian angles which
+
(2) Kiselev, A. V. Discuss. Faraday Soc. 1965,40, 205. (3)Kiselev, A. V. Gas Chromatography, 1964, Proc. Symp.: London, 1965; p 238. (4) Ash, S. G.; Kiselev, A. V.; Kuznetsov, B. V. Trans. Faraday Soc.
1971,67,3118. (5) Curthoys, B.;Davydov, V. Ya.; Kiselev, A. V.; Kiselev, S. A.; Kuznetaov, B.V. J. Colloid Interface Sci. 1974,48, 58. (6) Avgul, N. N.; Bezus, A. G.; Dobrova, E. S.; Kiselev, A. V.J. Colloid Interface Sci. 1973,42, 486. (7)Kiselev, A. V.;Poshkus, D. P. Trans. Faraday SOC.1963,59,176.
characterize the molecular orientation. This approach assumes quasi-rigidity of the adsorbate molecule and involves multiple integration of the exponential term for all possible configurationsof the molecule with respect to the adsorbent structure. Obviously, the exact computational procedure and allowable approximations must depend on the nature of the system and in particular on the complexity of the adsorbent. It was not surprising therefore that the treatment was found to be more successful when applied to molecules adsorbed on the basal plane of graphite8 than by X or Y zeolite^.^ In order to obtain agreement between the theoretical and experimental values of K1, Kiselev introduced an empirical scaling factor 6 for the correction of 4. Values of p were proposedgin the range 0.84-0.94, but the theoretical basis for this adjustment remained obscure and it was recognized that more work would be required on a number of carefully prepared zeolite crytals before a clear picture could emerge of the disposition and orientation of adsorbate molecules within the zeolite intracrystalline pore structure. Kiselev was one of the first to appreciate the advantages of gas chromatography for studying adsorption at the gas/solid interface and his pioneering work3J0in the 1960s attracted considerable attention. However, it was in the closing stage of his career that he introduced” a novel method for structural characterization, which he called “chromatoscopy” (or chromatostructural analysis). The method entailed gas chromatographic determination of the Henry’s law constant in conjunction with application of the molecular statistical theory of adsorption: its utility depended on the fact that the intermolecular interaction of an isolated adsorbed molecule with a homogeneous, flat adsorbent surface was dependent on the molecular geometry of the adsorbate. At present it is impossible to predict the full scopy of chromatoscopy, but the method has already been shown12 to be of value for investigating the structures of a variety of organic molecules adsorbed on graphitized carbon black. If the full potential of this interesting approach is to be realized, it will be necessary to improve the degree of surface homogeneity of a range of well-characterized adsorbents. We have seen that Kiselev was not always fortunate in his choice of adsorbents, but there is no doubt that he had the good fortune (or perhaps the perspicacity) to have brought together an extremely loyal and talented group of co-workers-some of whom remained with him for over 30 years. In this short review it has been possible to mention only a few of Kiselev’s scientific achievements and this is hardly likely to convey an adequate impression of the monumental quality of his work. Looking back over a period of 30 years, one can admire the work of a master craftsman and it is tempting to compare Kiselev’s approach to science with that of the architect setting out to design a cathedral. There is every reason to suppose that the scale and attention to detail of Kiselev’s work will long be remembered. Those who were fortunate enough to know him will recall a modest and friendly person with a strong sense of humor and old-world courtesy. (8) Kiselev, A. V.; Poshkus, D. P.; Grumadas, A. J. J. Chem. Soc., Faraday Trans. 2 1979,75,1281, 1288. (9)Kiselev, A. V. J. Chem. Tech. Biotechnol. 1979,29,673.Kiselev, A. V.;Quang Du, Pham. J . Chem. Soc., Faraday Trans. 2 1981,77,17. (10)Kiselev, A. V. In Advances in Chromatography; Giddings, J. C., Keller, R. A., Eds.; Marcel Dekker: New York, 1967;p 113. (11) Kiselev, A. V. Chromatographia 1978,11, 691. (12)Kiselev, A.V.; Poshkus, D. P. Faraday Symp., Chem. Soc. 1980, No. 15, 13.
