Pickett Equation for the Description of Adsorption on Arbitrary Surfaces

The theory of multilayer adsorption of gases, namely the Pickett equation, has been developed to the case of adsorption on arbitrary surfaces in a molecular and a topological approach. We present the prediction of the fractal dimension for the surface of an adsorbent and for the set of interfaces generated by the growing of layers. The theoretical models correctly predict quantities and qualitative features of the experiment for two systems: adsorption of water vapor (T = 298 K) on the sample of lunar regolith and of nitrogen (T = 77 K) on a coal sample

Analytical equation for the mesopore size distribution function of open cylindrical capillaries

For the characterization of porous structures, besides the specific surface area, the pore size distribution is of special interest. In this paper, the pore size distribution of mesoporous structures is calculated from the adsorption branch of the hysteresis loop, whereby only loops of type H1 are considered. The modeling is done only for cylindrical capillaries and the calculation of the pore size distribution is done by a combination of the percolation theory and the theory of capillary condensation. By applying percolation theory to the adsorption process, the pressure dependence of pore filling during capillary condensation is described. Because of a lack of strictly theoretically based equations for the adsorption process by capillary condensation, a mathematical adaptation to measured data is done by the Bernoulli equation. This is proposed by the authors for the first time for a description of adsorption–desorption processes. Thus a new, strictly thermodynamic method to calculate the mesopore size distribution is gained. As an example, the pore size distribution is calculated. The results coincide well with other evaluation methods

SOME ADSORPTION ASPECTS OF CATIONITES GIDRATATION

Correlations dependences are set between the determining parameters the Pickett equation of multi-layer adsorption and hydration properties of carboxylic- and sul-phurcationites in form ions of alkaline and alkaline-earth metals

Scaling Approach for Estimating Pore Connectivity Coefficient for Open Slit-Like Capillaries

To estimate the pore connectivity coefficient for open slit-like capillaries, the qualitative and quantitative description of adsorption hysteresis based on the Frenkel–Halsey–Hill formalism is used. A scaling-related governing equation is derived that provides a generalized description of the desorption branch of the hysteresis loop. The proposed equation is shown to be capable for an adequate description of data for several experimental systems, which leads to reliable values of the pore connectivity coefficient

Van der Waals equation for the description of monolayer formation on arbitrary surfaces

The van der Waals equation is well known for the description of two-dimensional monolayers. The formation of a monolayer is the result of a compromise between the process of self-organization on the surface and the probabilities of spatial configurations of adsorbate molecules near the surface. The main reasons for the geometric heterogeneity of the monolayer are the geometric disorder and the energy inhomogeneity of the surface profile. A monolayer is a statistically related system and its symmetry causes correlations of processes at different spatial scales. The classical van der Waals equation is written for the two-dimensional, completely symmetric Euclidean space. In the general case, the geometry of the monolayer must be defined for the Euclidean space of fractional dimension (fractal space) with symmetry breaking. In this case, the application of the classical van der Waals equation is limited. Considering the fractal nature of the monolayer–solid interface, a quasi-two-dimensional van der Waals equation is developed. The application of the equation to experimental data of an activated carbon is shown

Irreversible Adsorption Deformation of Layer Structures

In the framework of macroscopic thermodynamics of deformation, expressions are proposed for the calculation of deformation isotherms along the adsorption and desorption branches of the hysteresis loop within the linear and elastic deformation domains. With the assumption of spatially homogeneous (in the statistical sense) medium and scale-invariant behaviour of the relaxation rate, the generalized equation is proposed for the calculation of the hysteresis loop throughout the entire range of the adsorbate pressure in the bulk phase. In this equation, the irreversibility parameter is the governing one. The proposed equations are verified for the benzene adsorption–desorption isotherm on the organosubstituted synthetic fluorhectorite

Non-Arrhenius form of the Henry adsorption on inhomogeneous substrates: The effect of frozen disorder

Usually, when considering sub-monolayer adsorption at different temperatures T, the logarithm of the Henry constant is represented as (Formula presented.) with some constant “heat of adsorption” U0 > 0. However, such Arrhenius-type form has a clear base only for an ideal translational-invariant crystal substrate. In more real situation, e.g. for a structurally disordered substrate, the “heat of adsorption” will be some random function of two-dimensional coordinates characterized by some distribution function of its different values. Starting from general principles of the theory of Gaussian fluctuations, we show that the adsorption at the substrate with bulk inhomogeneous structure leads to expression (Formula presented.) with some fluctuation quantity Δ. A possibility to observe such “non-Arrhenius” additive seems most favorable at rather low temperatures for substrates modeled by substitutional solid solutions. The theoretical predictions are illustrated by comparison with the experimental data obtained for some disordered adsorbents