Krzysztof Nieszporek

On the theoretical origin and applicability of the potential theory approach to predict mixed-gas adsorption on solid surfaces from single-gas adsorption isotherms

Abstract A rigorous theoretical development of the Potential Theory Approach for predicting mixed-gas adsorption on solids from single-gas adsorption isotherms is given. That approach requires very simple computer calculations making it very attractive for process design and control in industrial applications of mixed-gas adsorption on solids. It is shown that the “coalescence” operation can be treated as a purely numerical operation not involving the knowledge or assumptions about some physical quantities the meaning of which is not clear. However, it is also shown that the traditional coalescence operation is not the best way to elucidate the values of the parameters which are necessary to predict mixed-gas adsorption equilibria. A more effective way to determine the values of these parameters better, based on a theoretical analysis of single-gas adsorption isotherms, is proposed.

Adsorption of phenols from aqueous solutions: Equilibria, calorimetry and kinetics of adsorption

The brief theoretical description of the phenols adsorption from aqueous solutions on carbonaceous adsorbents, i.e. activated carbons (ACs) and activated carbon fibers (ACFs) has been presented. The description includes adsorption equilibria, calorimetry as well as kinetics of adsorption. The generalized Langmuir-Freundlich (GLF) isotherm equation has been used to study of the cooperative effect of the surface heterogeneity and the lateral interactions between the admolecules. Theoretical isosteric heats of adsorption connected with the GLF model have been estimated too. Knowledge of both adsorption equilibria and heats of adsorption is fundamental for adequate description of any adsorption process. To correlate the kinetic data of the studied systems, the theoretical equations developed from Statistical Rate Theory (SRT) of Interfacial Transport were applied. The most advantageous of the proposed model of calculations is the set of common parameters appearing in each type of expressions, which significantly extends the possibility of their interpretation. Theoretical studies were fully reviewed using the literature experimental adsorption data. They included the data of phenols adsorption both on ACs and ACFs surfaces.

On the Correct Use of the Dubinin-Astakhov Equation to Study the Mixed-Gas Adsorption Equilibria

This paper presents the possibilities of Integral Equation (IE) approach to study the mixed-gas adsorption equilibria. As a result, the generalizations of Dubinin-Astakhov equation for the case of mixed-gas adsorption are presented. These new equations are examined using a few adsorption systems recently published in literature.

Application of the Integral Equation Approach to the Study of Enthalpic Effects Accompanying Mixed-Gas Adsorption on Heterogeneous Solid Surfaces

The possibilities of the Integral Equation approach for describing mixed-gas adsorption equilibria are presented. In this study, the energetic heterogeneity was described through the use of the Gaussian-like adsorption energy distribution function. As a result, very simple equations describing the isosteric heats of mixture components were obtained. The advantage of the model presented is the possibility of predicting the phase diagrams and enthalpic effects accompanying mixed-gas adsorption from a theoretical viewpoint based on pure-component adsorption data. New equations for isosteric heats of component mixtures were examined using the experimental data obtained by Dunne et al. (1996a, b, 1997), i.e. C2H6, CH4 adsorbed on silicalite and CO2, C2H6 adsorbed on NaX zeolite. The calculations are relatively simple and can be applied industrially.

The Balance between Diffusional and Surface Reaction Kinetic Models: A Theoretical Study

In this work we considered the factors determining the rate of adsorption. By assuming the balance between the surface reaction and diffusional mechanisms we discussed the possibility to conclude which model is the rate-controlling step. By using the pseudo first-order Lagergren equation we showed the theoretical interpretation of the Lagergren coefficient. If this parameter is time-dependent, the diffusional model should be assumed to represent the kinetics of adsorption. Such property can be utilized practically to resolve the rate-determining step. We also discussed the influence of surface energetic heterogeneity on the mechanism of the rate of adsorption.

The application of NIAS approach to describe enthalpic effects accompanying mixed-gas adsorption

Abstract The possibilities of the non-ideal adsorbed solution (NIAS) approach to study enthalpic effects accompanying mixed-gas adsorption equilibria is presented. Besides heterogeneity the interaction effects are taken into account. The obtained theoretical expressions for predicting isosteric heats of adsorption in the gas mixture are relatively simple and accurate. To predict phase diagrams and calorimetric effects in the mixed-gas adsorption only the knowledge of single-gas adsorption isotherms and accompanying calorimetric effects is required.

Multimodal, pH Sensitive, and Magnetically Assisted Carrier of Doxorubicin Designed and Analyzed by Means of Computer Simulations

This work deals with an analysis of drugs carriers based on the structure of a carbon nanotube using large-scale atomistic molecular dynamics simulations. The analyzed systems link several functions in a single architecture. They are as follows: (i) the sidewalls and tips of carbon nanotubes are covalently functionalized by polyethylene glycol-folic acid conjugates, and this approach allows for creation of hydrophytic and biocompatible systems; (ii) doxorubicin is kept in the internal space of a carbon nanotube as a mixture with dyes (p-phenylenediamine or neutral red)-it allows for pH-controlled release or alteration of the interaction topology; (iii) the mixture of doxorubicin and dyes in the nanotube interior is additionally sealed by fullerene nanoparticles which act as pistons at acidic pH and loosen the tangle of polyethylene glycol chains at the nanotube tips. This enhances the release of doxorubicin from the nanotube when compared to the analogous system but without the fullerene caps; (iv) another function of the carrier can be activated by filling of the fullerenes by magnetic material-then, the carrier can be visualized by means of magnetic resonance imaging, it can realize magnetic hyperthermia of tumor cells, and intense rotation of the nanoparticles can be induced by the application of an external magnetic field. That rotation enhances the release of doxorubicin from the nanotube and leads to the increase of the rotational temperature. The studies show that the proposed design of the drug-doxorubicin carrier reveals very promising properties. Its fabrication is absolutely feasible, as all individual stages necessary for its construction have been confirmed in the literature.

Adsorption of Binary Gas Mixtures on Strongly Heterogeneous Surfaces

The integral equation (IE) approach coupled with a rectangular adsorption energy distribution and Mean Field Approximation (MFA) is used to describe the adsorption of single gases and their binary mixture on a heterogeneous solid surface. In particular, it is important to stress that all theoretical expressions shown are the exact solution of IE approach. During the analysis of single-gas adsorption isotherms also accompanying calorimetric effects are investigated. The problem of correlations between the best-fit parameters describing energetic heterogeneity and energy of intermolecular interactions is discussed. The predictions of the theory are compared with the experimental literature data. It is shown that the new theoretical adsorption isotherms give the results that are very close to the experimental data.

Comparative Study of the Theoretical Predictions of Mixed-gas Adsorption Equilibria from Pure Component Adsorption Data: Vacancy Solution Theory

Simple methods for describing mixed-gas adsorption equilibria based on a knowledge of single gas adsorption are still needed for gas separation processes. The present paper describes the possibilities of the Vacancy Solution Theory (VST) approach. The VST predictions are compared with results obtained using the IAS, IE and PT approaches as presented earlier by the author.

The inhibition effect of water on the purification of natural gas with nanoporous graphene membranes

Molecular dynamics simulations are used to investigate the inhibiting effect of water on the natural gas separation with nanoporous graphene. The membrane separation process involves CH4 + N2 mixtures with and without the addition of water. The results show that water is able to form hydrogen bonds with nitrogen atoms located in a nanopore rim. This effect causes a decrease of separation selectivity as well as a reduction of gas permeation. In the extreme case, when the nanopore rim contains only nitrogen atoms, water agglomerates at the center of the nanopore and effectively closes down the permeation path. The conclusions are confirmed by the analysis of stability and kinetics of hydrogen bonds.