Dubinin-Serpinski

The Dubinin-Serpinski (DS) equation, which was based on this model, can be expressed in the form... 

The surface chemical properties of the carbon materials were characterized as follows measurement of pH of carbon slurries (in 0.1 M NaCl solution) [89] neutralization with bases of different strength and dilute HCl according to Boehm s method [63,66] determination of total oxygen/nitrogen content by elemental analysis (with an accuracy of 0.2%) [170] mass loss of carbon samples after heat treatment in a vacuum. Additionally, the number of primary adsorption centers (a,)) was determined from water vapor adsorption isotherms according to the Dubinin-Serpinsky method [171], as was the heat of immersion in water for selected samples [111,172]. The results of these operations are pre.sented in Table 3. For all samples transmission Fourier Transform Infrared (FTIR) spectra and X-ray photoelectron spectra (XPS) were recorded. 

Dubinin-Serpinski Equation for Water Adsorption on Carbon... 

This adsorption equation, known as the Dubinin-Serpinsky (D-Se) equation, exhibits a type V isotherm as shown in Figure 4.2-5 for c mmole/g and three... 

Figure 4.2-5 Plot of the Dubinin-Serpinski equation versus P/Pq with c = 3, C o = 1 mmol/g...

Being a three parameter equation, the Dubinin-Serpinsky equation (4.2-15) can be used directly in a nonlinear optimisation routine to determine the optimal parameters. Alternatively, the initial adsorption data can be used with eq. (4.2-17) to determine the constant c and the concentration of the primary site, and the equation for the maximum capacity (4.2-19) then can be used to determine the remaining parameter k. 

Figure 4.2.6 shows plots of the above data as well as fitted curves (obtained from the ISO FITl program) from the Dubinin-Serpinski equation and the DA equation. Both of these equations fit the data reasonably well although the Dubinin-Serpinski equation provides a better fit in the lower range of the pressure. This could be attributed to the correct description of the water clustering in the lower pressure range. 

Figure 4.2-6 Fitting the Dubinin-Serpinski equation to water/activated carbon data...

The adsorption of water vapour has been studied with a range of microporous carbons, zeolites and aluminophosphates in order to elucidate the relative influence of surface chemistry, pore size and pore shape upon the form of the water isotherm. It was possible to separate the adsorbents into three groups on the basis of their affinity and capacity for water vapour. The porous carbons were further examined using the BET and Dubinin-Serpinsky equations. The results show that the adsorption of water vapour at low p/p° is largely dependent upon specific adsorbent-adsorbate interactions whilst at higher relative pressures the micropore size and shape control the extent of adsorption. It is proposed that hydrogen-bonded layers of water can be more readily accommodated in the narrow slit shaped pores (-0.5nm) of molecular sieve carbons than in tubular pores of similar width (e.g. Silicalite/ZSM-5). 

In order to further elucidate the complex pore filling process in microporous carbons, the empirical Dubinin-Serpinsky (DS) equation (refs. 14-15) was used to assess the influence of polar sites on the shape of the isotherm. This equation was developed from the concept of adsorption of water molecules at uniform high energy primary adsorption centres. Molecules adsorbed on these sites act as secondary adsorption centres via a hydrogen-bonding mechanism. Thus, this model does not refer explicitly to the role played by pore size. The DS equation may be written in its modified form (ref. 15) as ... 

Fig. 5. Quadratic fit of the Dubinin-Serplnsky fjg g. Quadratic fit of the Dubinin-Serpinsky equation to JF144 experimental data. equation to KCC1 experimental data.

H.H. Dubinin, V.V. Serpinsky and K.O. Murdmaa (Eds.), Adsorption and Adsorbents (Russ.) (Proc. 6th Allunion Conf. Adsorption Theory, Moscow, November 18-21, 1985), Nauka, Moscow, 1987. 

Dubinin M M (1975) In Progress in Surface and Membrane Science, vol 9 (D A Cadenhead, ed), Academic Press, New York, p 1 Dubinin M M (1980) Carbon 18, 355 Dubinin MM and Serpinski V V (1981) Carbon 19,402 Emmett PH and DeWitt T (1941) lnd Eng Chem Anal Ed 13,28 Everett DH andPowlJC (1976)/ Chem Soc. Faraday Trans 172,619 Everett DH and Ward RJ (1986)/ Chem Soc. Faraday Trans 782,2915 Femandez-Cohnas J, Denoyel R, Gnllet Y, Rouquerol F and Rouquerol 1 (1989a) Langmuir S, 1205 Femandez-Colinas J, Denoyel R and Rouquerol J (1989b) Adsorption Sci Techn 6,18 Freeman J J and Sing KSW (1991) In Adsorptive Separation (M Suzuki, ed), Institute of Industrial Science, Tokyo, p 261... 

Dubinin, M.M., Bering, B.P., Serpinsky, V.V., and Vasil ev, B.N. (1958). The properties of substances in the adsorbed state studies of gas adsorption over a wide temperature and pressure range. In Surface Phenomena in Chemistry and Biology (J.F. DanieUi, K.G.A. Pankhunt and A.C. Riddiford, eds). Pergamon Press, pp. 172-88. 

Dubinin (Institute of Physical Chemistry, the U.S.S.R. Academy of Sciences, Moscow) and colleagues (Zaverina, Radushkevich, Timofeev, Bering, Serpinsky, Zhukovskaya, Nikolaev, Sarakhov, Isirikyan, Zolotarev, Yakubov, Bakaev, Onusaitis, Voloshchuk, and others) conducted a theoretical analysis of the sorption phenomena in porous substances, including silica, and applied these phenomena in practice (6-11). 

A. Kiselev developed the adsorption-structural method of investigation (129), which made possible a rational classification of adsorbents (130-132). Dubinin, Radushkevitch, Bering, Serpinsky, and others have developed on the basis of their experimental results a theory on the physical adsorption of gases and vapors in microporous adsorbents that they call the theory of volume filling of micropores. The theory is applicable to almost all the adsorption systems, including microporous silica gels and porous glasses (133, 134). 

Larionov, O. G. Kurbanbekov, E. In Physical Adsorption from Multi-Component Phases Dubinin, M. M., Serpinsky, V. V., Eds. Nauka Moscow, 1972 p... 

---