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Adsorption: Journal of the International Adsorption Society (v.19, #2-4)

Editorial: Effects of surface heterogeneity in adsorption and catalysis on solids by Wladek Rudziński (pp. 209-210).

Charging of water at inert and hydrophobic surfaces. Effect on interfacial properties of silver halides by Nikola Kallay; Filip Šupljika; Tajana Preočanin (pp. 211-216).

Isoelectric point of silver halides depends on pH due to charging of interfacial water layer. The isoelectric point of water at inert and hydrophobic surfaces lies at pH≈3 so that water at surfaces is negatively charged in the pH region above 4. Consequently the electroneutrality point of silver halides pAg_eln in aqueous environment, with respect to adsorption of silver and halide ions, does not correspond to the isoelectric point pAg_iep measured at pH≈6, as previously assumed. The effect of assumed value of pAg_iep was examined. The equilibrium constants for adsorption of silver and halide ions on silver chloride and silver bromide were calculated for the range of assumed pAg_iep values ranging from isoelectric points measured at pH=6 to pH=3. The values of pAg_iep obtained at pH=3 was taken as pAg_eln and the corresponding equilibrium constants of interfacial reactions were obtained.

Keywords: Single crystal electrode; Silver chloride; Silver bromide; Surface potential; Electrical interfacial layer; Equilibrium parameters; Interfacial water layer

Zeta-potential measurements of OTS-covered silica samples by Johannes Lützenkirchen; Christine Richter (pp. 217-224).

We have carried out zeta-potential measurements on two different OTS (octadecyl-trichlorosilane)-covered silicas (fused silica, quartz 0001) prepared under identical conditions. Streaming current measurements on the fused silica supported OTS sample indicate a well reproducible IEP of 3.5. The major part of the study focused on the quartz 0001 supported sample with an IEP lower than that of the fused silica support and in agreement with that found in a spectroscopic study. The IEP in water (on addition of HCl) was found at around pH 3, and appeared to shift to lower values in three subsequent measurements. A final measurement after a separate series in KCl media gave the same IEP as obtained in the very first measurement, suggesting that the experiments did not significantly change the interfacial properties despite a large number of experiments. In one series of measurements care was taken to exclude any cations other than protons from the measurements, such that protons are the only counter-ions to the negative net charge.While our IEPs with the quartz support agree well with recent estimates from sum frequency generation (SFG) investigations, none of the zeta-potential vs pH curves would mimic a pattern experimentally observed in the amplitude of the “ice-like” water band between pH 3.5 and 5 in that SFG study. Furthermore, our results do not indicate any significant chloride-ion adsorption in KCl systems, but instead the shift of the IEP with increasing KCl to higher pH values rather indicates specific effects of potassium ions. Under conditions more relevant to the spectroscopic study (i.e. in absence of potassium) no specific pattern reminiscent of the SFG results was found. When tested it was found that surface conductivity was negligible.

Keywords: Hydrophobic surface; Hydroxide adsorption; OTS; Zeta-potential

In situ small angle X-ray scattering and benzene adsorption on polymer-based carbon hollow fiber membranes by Evangelos P. Favvas; Konstantinos L. Stefanopoulos; Sergios K. Papageorgiou; Athanasios C. Mitropoulos (pp. 225-233).

The structural changes and the mechanism of benzene adsorption on microporous carbon hollow fiber membranes with different surface and pore network properties have been investigated by in situ small-angle X-ray scattering (SAXS) and benzene adsorption. Benzene adsorption measurements have been carried out in situ with SAXS alongside an adsorption/desorption isotherm cycle at 293 K with the aid of a specially constructed adsorption sample cell. In addition low-pressure C₆H₆ and high-pressure CO₂, CH₄ and N₂ adsorption isotherms have been performed. Two carbon hollow fiber membranes, both prepared by controlled pyrolysis procedures of polyimide membrane precursor, were under study. During benzene adsorption the intensity of the SAXS curves changes in a way that depends on how the pores are filled and the contrast fluctuations occur. The SAXS data have been modeled by evaluating the form factor of lamellar micropores upon filling with C₆H₆. The existence of ultra micropores within the surrounding matrix was also taken into account. The results suggest that the arrangement of the ultra micropores on the non-activated membrane is in such a way that the access of benzene to the micropores is restricted, resulting in an incomplete filling. On the other hand, the activation process generates a more accessible pore network where the micropores are completely filled.

Keywords: In situ; SAXS; Carbon membranes; Adsorption; Lamellar pore; Form factor

Abnormally high heat generation by transition metals interacting with hydrogen and oxygen molecules by A. J. Groszek (pp. 235-240).

Abnormally high heats, exceeding 2000 kJ/mol (20 eV) per molecule of O₂, are generated by interaction of the oxygen with the hydrogen absorbed on palladium, gold and nickel particles at 25 °C to 220 °C. The highest heats were observed when the metals were treated with micromole quantities of argon, prior to absorption of hydrogen, as well as its interactions with metal particles reaching nanometer size. In the latter case the heat evolutions due to the interactions with hydrogen were approaching 5000 kJ/mol. The interactions with oxygen in inert gas environments, such as that of argon, yielded higher heat evolutions than those given by pure O₂ pulses injected into nitrogen carrier gas.The results revealed an important role of argon in increasing the intensity of atomic hydrogen-oxygen reactions to a level several times higher than the heat of water formation from molecular hydrogen and oxygen.

Keywords: Flowmicrocalorimetry; Heats of adsorption; Hydrogen absorption; Oxygen absorption; Hydrogen and oxygen absorption on palladium; Gold and nickel

The effect of organic sorbates on water associated with environmentally important sorbents: estimating and the LFER analysis by Mikhail Borisover (pp. 241-250).

The effect of organic sorbates on the water associated with naturally occurring sorbents is of significant interest since it probes the hydration of a sorbate-specific microenvironment and its role in a compound partitioning between various environmental compartments. This effect was described in a thermodynamically strict way by converting the sorption isotherms of organic vapors on variously hydrated sorbents into the derivatives relating the change in the amount of water associated with a sorbent to the change in the amount of an organic sorbate. Further, these derivatives were analyzed by means of the Linear Free Energy Relationship (LFER). The analysis included the sorption data for various organic vapors on such environmentally important sorbents as quartz, metal oxides, calcite, clay minerals and humic acid. From the LFER analysis it followed that (i) organic sorbate polarizability contributions from n- and π-electrons resulted in driving water into the sorbent phase; (ii) the increasing volume of the organic compounds involved expelling water molecules; (iii) the increasing hydrogen-bond acidity and basicity of organic sorbates resulted in expelling water from inorganic surfaces but in enhancing hydration of the humic phase. In contrast to inorganic surfaces, when sorbed on strongly hydrated humic acid, the majority of organic sorbates containing oxygen, nitrogen or sulfur atoms drive water into the sorbent phase. Several molecules of water may need to be cosorbed by a humic sorbent for each sorbed molecule of an organic compound thus supporting the possibility of the concomitant participation of a number of water molecules in organic sorbate–humic matter interactions.

Keywords: Sorption; Organic compounds; Distribution; Hydration effect; Mineral surfaces; Humic matter

Preparation of multi metal–carbon nanoreactors for adsorption and catalysis by Suranjana V. Mayani; Vishal J. Mayani; Jun Young Lee; Sung Hyun Ko; Soo Keun Lee; Sang Wook Kim (pp. 251-257).

Metal–incorporated composite carbon materials have engendered great progress in the fields of catalysis, energy storage and material science because of their size and chemical and physical properties. In this study, a modern technique was applied for the development of multi metal–carbon nanoreactors (MCNRs) from a pristine carbon cage (CC) using template method with nano silica ball (NSB), pyrolysis fuel oil (PFO) and metal nanocrystals such as gold, copper, nickel, potassium and manganese. The newly prepared Au, Cu, Ni, K and Mn deposited carbon nanoreactors were fully characterized by various analytical techniques. Due to their easy fabrication protocols and broad potential applications, the MCNRs were used successfully for the chemisorptions of hydrogen and ethylene gases alongside the solvent–free heterogeneous catalytic oxidation of a secondary alcohol. The MCNRs have exhibited dynamic adsorption performance and excellent catalytic activity.

Keywords: Adsorption; Heterogeneous catalysis; Metal–carbon; Nanoreactors; Pyrolysis fuel oil

Evaluation of surface potential from single crystal electrode potential by Tajana Preočanin; Nikola Kallay (pp. 259-267).

The new method of evaluation of the point of zero potential for the metal oxide exhibiting a saddle-like surface potential function Ψ ₀(pH), as obtained by acid base potentiometric titration using Single Crystal Electrode, was proposed. The electrode potential of sapphire single crystal electrode (A crystal plane, $11ar{2}0$ ) was measured, point of zero potential and surface potentials were evaluated, and the results were analyzed using the Surface Complexation Model. The electroneutrality point corresponding to the point of zero potential was found to be at pH_pzp=7.0. Thermodynamic protonation equilibrium constants for the first and the second step of protonation were obtained as $lg K_{1}^{circ} = 12.7$ ; $lg K_{2}^{circ} = 1.2$ .

Keywords: Single crystal electrode; Sapphire; Surface potential; Electrical interfacial layer; Surface complexation; Equilibrium parameters; Surface charging

Carbon nanotubes as potential material for drug delivery—experiment and simulation by Artur P. Terzyk; Marek Wiśniewski; Katarzyna Dulska; Agnieszka Bielicka; Piotr A. Gauden; Sylwester Furmaniak; Karolina Werengowska-Ciećwierz (pp. 269-272).

We discuss the factors influencing the properties of new drug delivery system, composed of carbon nanotubes and analgesic antipyretic drug—paracetamol. Basing on experimental data it is shown, that by a simple manipulation with the heating time at the stage of system preparation, one can easily change the rate of the drug delivery. Moreover, this rate can be changed in a very wide range. Finally, using Molecular Dynamics simulation we also discuss the orientation and properties of drug molecules at different stages of the hot melt deposition process.

Keywords: Drug delivery; Paracetamol; Nanotubes; Hot melt drug deposition

Sorption properties of activated carbons obtained from corn cobs by chemical and physical activation by Justyna Kaźmierczak; Piotr Nowicki; Robert Pietrzak (pp. 273-281).

The paper presents results of a study on obtaining activated carbon from common corn cobs and on its use as adsorbent for removal of pollution from liquid and gas phases. The crushed precursor was subjected to pyrolysis at 500 and 800 °C in argon atmosphere and next to physical or chemical activation by CO₂ and KOH respectively. The effect of pyrolysis conditions and activation method on the physicochemical properties of the materials obtained was tested. The sorption properties of the carbonaceous adsorbents obtained were characterized by determination of nitrogen dioxide and hydrogen sulphide sorption from gas stream in dry and wet conditions as well as by iodine and methylene blue removal from aqueous solution.The final products were microporous activated carbons of well-developed surface area varying from 337 to 1213 m²/g and showing diverse acid-base character of the surface. The results obtained in our study have proved that a suitable choice of the activation procedure for corn cobs permits production of cheap adsorbents with high sorption capacity toward toxic gases of acidic character as well as different pollutants from liquid phase.

Keywords: Waste corn cobs; Activated carbons; Pyrolysis, activation; NO₂/H₂S removal; Iodine and methylene blue adsorption

Two-dimensional molecular sieves: structure design by computer simulations by Adam Kasperski; Paweł Szabelski (pp. 283-289).

Nanoporous molecular networks formed spontaneously by organic molecules adsorbed on solid substrates are promising materials for future nanotechnological applications related to separation and catalysis. With their unique ordered structure comprising nanocavities of a regular shape planar networks can be treated as 2D analogs of bulk nanoporous materials. In this report we demonstrate how the Monte Carlo simulation method can be effectively used to predict morphology of self-assembled porous molecular architectures based on structural properties of a building block. The simulated results refer to the assemblies created by cross-shaped organic molecules which are stabilized by different intermolecular interactions, including hydrogen bonding and van der Waals interactions. It is demonstrated that tuning of size and aspect ratio of the building block enables the creation of largely diversified extended structures comprising pores of a square and rectangular shape. Our theoretical predictions can be helpful in custom design of functional adsorbed overlayers for controlled deposition, sensing and separation of guest molecules.

Keywords: Self-assembly; Adsorption; Porous overlayers; Computer simulations

Effects of melting and ordering on the isosteric heat and monolayer density of argon adsorption on graphite by Eugene A. Ustinov; Duong D. Do (pp. 291-304).

The aim of this paper is to study the effects of temperature on the state of the adsorbed argon on an uniform graphite surface. We applied the kinetic Monte Carlo scheme to simulate adsorption over a very wide range of temperature, which allows us to model the vapor–solid, the vapor–liquid and the order–disorder transition of the monolayer. The main distinction of our methodology is that it accounts for the lattice constant change with loading in the case of formation of an ordered molecular layer by appropriately changing the simulation box size. To do this we enforced the equality of the tangential pressures obtained by the virial and thermodynamic routes, which corresponds to the minimum Helmholtz free energy of a system at a given number of molecules and volume. This criterion is a consequence of the Gibbs–Duhem equation. A significant result obtained by application of the new simulation method was a sharp contraction of the monolayer just after its completion and the onset of the second layer. It manifests itself in an additional heat release. We re-determined the 2D-melting and 2D-critical temperatures of the molecular layer of argon. We also analyzed the order–disorder transition above the 2D-melting and showed that it could occur at some temperatures above the 2D-critical temperature. In this case, a hexagonal lattice appears at a sufficiently large tangential pressure. The effects of loading on the lattice constant, the 2D-critical temperature of the order–disorder transition and the differential heat of adsorption are thoroughly discussed.

Keywords: Kinetic Monte Carlo; Adsorption on graphite; Monolayer phase transition; Heat of adsorption

Confined space effects driving to heterogenization of solutions at the interfaces by V. M. Gun’ko; V. V. Turov; R. Leboda; J. Skubiszewska-Zięba; B. Charmas (pp. 305-321).

Water and concentrated solutions of acids (HCl, H₃PO₄, and H₃PO₃) or H₂O₂ are clustered at the interfaces of nanosilicas and multi-layer graphene oxide (MLGO) as shown by low-temperature ¹H NMR spectroscopy. The acid solutions in contact with silica or MLGO powders placed in nonpolar (CCl₄) or weakly polar (CDCl₃) media form nanodomains and clusters of several types and sizes with different contents of water and solutes. This differentiation of the solutions is stronger at a surface of more compacted nanosilicas because of enhanced confinement effects in narrower pores (voids) between adjacent nanoparticles. For MLGO, the confined space effects are relatively weak but the formation of ice crystallites during freezing of the suspension changes the material texture. Obtained results are of importance for deeper insight into the mechanism of the interfacial behavior of complex solutions under different confined space effects and due to the influence of organic co-solvents.

Keywords: Nanosilica; Multilayer graphene oxide; Interfacial water; HCl solution; Phosporus oxyacids; H₂O₂ ; Low temperature ¹H NMR spectroscopy; Cryoporometry

Study of CO₂ adsorption in functionalized carbon by Diana P. Vargas; L. Giraldo; J. C. Moreno-Piraján (pp. 323-329).

We evaluated the ability of CO₂ adsorption in functionalized activated carbons granular and monolithic type, obtained by chemical activation of African palm stone with H₃PO₄ and CaCl₂. We made a comparison between two methods of incorporation of nitrogen groups: the impregnation method with NH₄OH solution and NH₃ gasification. The materials were texturally characterized by N₂ adsorption at 77 K, the isotherms shows obtaining microporous materials with surface areas between 545–1425 m² g⁻¹ and pore volumes between 0.22 to 0.53 cm³ g⁻¹. It was established that with the methodologies used for functionalization is increased content of nitrogen groups, was achieved a higher proportion of such groups when carrying out the process in liquid phase with NH₄OH. The incorporation of nitrogen groups in the material generates an increase of up to 65 % in the CO₂ adsorption capacity of the MCa2 (Monolith prepared with CaCl₂ solution at 2 %) sample. Was reached a maximum adsorption capacity of 344 mgCO² g⁻¹ in the MCa2FAL (sample MCa2 functionalized with NH₄OH solution) sample.

Keywords: Activated carbon; Chemical activation; Functionalization; CO₂ adsorption

In situ SAXS investigation of dibromomethane adsorption in ordered mesoporous silica by Evangelos P. Favvas; Konstantinos L. Stefanopoulos; Achilles Vairis; John W. Nolan; Karsten D. Joensen; Athanasios C. Mitropoulos (pp. 331-338).

A SAXS/WAXS apparatus with the aid of a specially designed sample cell capable for performing both SAXS and WAXS experiments was used for adsorption studies in nanoporous materials. The applicability of the instrument for structural investigations and its ability for adsorption experiments because of the advanced sample environment were demonstrated by carrying out in situ SAXS measurements during gas physisorption. SAXS profiles of ordered mesoporous silica were measured at selected equilibrium points alongside a dibromomethane (CH₂Br₂) adsorption isotherm at 293 K. SBA-15 was the adsorbent of choice because it consists of a regular 2D hexagonal array of cylindrical mesopores that gives rise to Bragg reflections in the small-angle regime. CH₂Br₂ was selected as a contrast-matching fluid because it has almost the same electron density as silica. We obtained high-quality data comparable to those resulting from experiments performed in synchrotron light sources which produce intense beams of x-rays and support advanced instrumentation for high-resolution diffraction and SAXS studies. The Bragg peaks of the pore lattice are clearly visible for the evacuated sample and at the early stages of the adsorption process. The intensity decrease and the elimination of the Bragg peaks for the saturated sample suggest that an almost perfect contrast matching was achieved. A model has been used for monitoring the fluid condensation and evaporation regime in SBA-15 by taking into account both the Bragg scattering and the diffuse scattering for spatially random pore filling. The results show the absence of spatial correlations between filled pores suggesting random pore filling.

Keywords: SAXS/WAXS; Adsorption cell; In situ; SBA-15; Hysteresis loop; Condensation/evaporation

CO and NO adsorption on VO x/SBA-15 catalysts: an FT-IR spectroscopic study by R. Bulánek; N. Drenchev; P. Čičmanec; M. Setnička (pp. 339-347).

The adsorption of CO and NO over VO x-SBA-15 mesoporous materials with different vanadium content was investigated by FT-IR spectroscopy. Vanadium complexes were reduced in situ by hydrogen atmosphere at 450 °C for 3 h. Spectra of reduced samples show increasing in intensity of silanol groups, caused by dissociation of V–O(Si) bonds and formation of new H–O(Si) bonds. Reduction occurs with formation of water. The band corresponds to overtone of V=O stretching modes decreases in intensity because of oxygen withdrawing from V=O species.Presence of V⁴⁺ and V³⁺ species was observed. Inspection of CO adsorbed IR spectra evidenced existence at least two different type of V³⁺–CO complexes on the silica surface differing in both stretching frequencies and complex stabilities. We did not found principal difference between spectra of absorbed CO at −196 °C on the samples with different concentration of vanadium, probably because of relative low degree of reduction. As well as heterogeneity of surface V³⁺ and V⁴⁺ species was evidenced by adsorption of NO. Both V³⁺ and V⁴⁺ ions possess two effective coordinative vacancies and as a result can adsorb two NO molecules forming dinitrosyls. A part of V³⁺ cations forms only mononitrosyls characterize by band at 1724 cm⁻¹. Results obtained after NO adsorption reveal existence of three different kinds of vanadium species. Probably two of them are isolated and associated vanadium sites. The third type of vanadium has different surrounding than other two types. It was demonstrated that NO is a better probe than CO for testing the oxidation and coordination state of reduced vanadium species.

Keywords: Vanadium; SBA-15; FT-IR; Carbonyls; Nitrosyls

Nanoporous carbons obtained by carbonization of copolymers impregnated by salts by M. Sobiesiak (pp. 349-356).

This paper demonstrates the results of research on influence of types of polymer and kinds of salts used for impregnation of the polymer on porous structure formation in the final carbonaceous product. The studies were performed in two stages. In the first stage, the role of polymer structure were mainly studied. To achieve the aim, three different porous copolymers (polyimide and two types of polyester) were impregnated with the same salts (NiSO₄, and the mixture of AgNO₃ and Gd(NO₃)₃). In the second part of the study, only one polymer (polyimide) was impregnated by three mixtures of salts (chlorides, nitrates and sulphates of K, Cu(II) and Fe(III)). This approach allowed to evaluate the impact of the mixture of salts on porosity of the carbons, which were to be prepared.The obtained results revealed that when the impregnation was applied as a method for activation and moulding of porosity of carbonaceous materials prepared from polymers, several factors should be taken into account. First of all, initial decomposition temperatures of the polymers and the salts should be compared to find out if carbonization and activation processes proceed simultaneously or not. If the copolymer was carbonized and gases were released from decomposing salts, they reacted each other and synergic effect of polymer and salts properties were observed. Such conditions favored the development of microporous structure of the obtained carbon. On the contrary, if the processes were separated in time because of high temperature of melting point of the salts more mesopores were retained.

Keywords: Nanoporous carbons; Impregnation of polymers; Salts impregnation; Carbon preparation; Porous structure formation; DFT

Abatement of hydrocarbons by acid ZSM-5 and BETA zeolites under cold-start conditions by B. Puértolas; J. M. López; M. V. Navarro; T. García; R. Murillo; A. M. Mastral; F. J. Varela-Gandía; D. Lozano-Castelló; A. Bueno-López; D. Cazorla-Amorós (pp. 357-365).

Simulated cold-start tests have been carried out to evaluate the performance of H-ZSM-5 and H-BETA zeolites as hydrocarbon traps under simulated gasoline car exhaust gases, paying special attention to the effect of water on their behaviour. It is concluded that the hydrothermal treatment of the zeolites in the acidic form contributes to the better performance of these materials as hydrocarbon traps since the stabilization of the zeolites takes place. Moreover, the decrease of the surface acidity of the zeolites results in an increase of the Si/Al ratio, which contributes to the decrease of the water affinity for adsorption sites. Thus, the competition with hydrocarbon molecules in the exhaust for the adsorption sites is reduced which increases their trap efficiency. The stabilized H-ZSM-5 is the zeolite that showed the best performance with a propene offset temperature of 240 °C, which should be high enough for the three-way catalyst to carry out its role as catalytic converter.

Keywords: Cold-start; Vehicle emissions; Zeolites; Hydrocarbon trap; Stability

Carbon dioxide and nitrogen adsorption on porous copolymers of divinylbenzene and acrylic acid by Carlos O. Arean; Elena Groppo; Wei Liu; Leticia F. Velasco; Jose B. Parra (pp. 367-372).

Porous copolymers of divinylbenzene (DVB) and acrylic acid (AA) having DVB:AA ratios of 6:4, 8:2 and 9:1 were prepared following a distillation-precipitation method, using toluene as the porogenic agent. The materials thus obtained, which showed specific surface area in the range of 380–600 m² g⁻¹ and pore volume in the range of 0.14–0.18 cm³ g⁻¹, were investigated as possible adsorbents for CO₂ capture from the flue gas of coal-fired power stations. For that purpose, the isosteric heat of adsorption (and CO₂ adsorption capacity) was analysed from N₂ and CO₂ adsorption equilibrium isotherms obtained over a temperature range. For CO₂, q _st resulted to be in the range of 27–31 kJ mol⁻¹ (the highest value corresponding to the 6:4 sample), while for N₂ a value of q _st ≈ 12 kJ mol⁻¹ was obtained. Equilibrium adsorption capacity for CO₂ (at ambient temperature and pressure) showed the value of about 1.35 mmol g⁻¹. These results are discussed in the broader context of corresponding literature data for CO₂ capture using protonic zeolites.

Keywords: Poly(DVB-co-AA) porous polymers; Gas adsorption; CO₂ capture

Experimental and theoretical study of D₂/H₂ quantum sieving in a carbon molecular sieve by A. Gotzias; G. Charalambopoulou; A. Ampoumogli; I. Krkljus; M. Hirscher; Th. Steriotis (pp. 373-379).

The present work aims at providing additional insight into the crucial effect of pore size and pressure on the adsorption of H₂ and D₂ in porous carbons by means of Grand Canonical Monte Carlo simulations in model slit micropores at 77 K. In order to address the quantum behavior of the molecules the Feynman–Hibbs corrected LJ interaction potential is used for fluid–solid and fluid–fluid interactions. Based on the GCMC isotherms for the two isotopes, D₂ selectivity over H₂ is deduced for pores with different sizes as a function of pressure. Furthermore, GCMC results are coupled with experimental high pressure H₂ and D₂ adsorption data at 77 K for a commercial carbon molecular sieve (Takeda 3A).

Keywords: H₂ adsorption; GCMC simulations; Pore size distribution; Carbon molecular sieves; Quantum sieving

Study of thermodynamic characteristics of CO adsorption on Li exchanged zeolites by P. Čičmanec; R. Bulánek; E. Frýdová; M. Kolářová (pp. 381-389).

The experimental thermodynamic characteristics of CO probe molecule adsorption on lithium exchanged zeolites of MFI, FAU, MCM-58, MCM-22, MCM-36 and MCM-49 structure was investigated by joint volumetry-calorimetry method. Consideration was given to the interpretation of the heat evolved when a probe molecule was adsorbed on the surface. In particular, the number and strength of adsorption sites were discussed as functions of zeolite structure and concentration of extra-framework cation. In addition, the obtained thermodynamic data and energy distribution functions were discussed together with results obtained from FTIR spectroscopy and theoretical DFT calculations.

Keywords: Carbon monoxide; Zeolites; Regularization; Calorimetry; Volumetry

Adsorption and desorption kinetics of benzene derivatives on mesoporous carbons by Adam W. Marczewski; Anna Deryło-Marczewska; Agata Słota (pp. 391-406).

Adsorption and desorption of benzoic and salicylic acids and phenol from a series of synthesized mesoporous carbons is measured and analyzed. Equilibrium adsorption isotherms are best described by the Langmuir–Freundlich isotherm. Intraparticle diffusion and McKay’s pore diffusion models, as well as mixed 1,2-order (MOE), integrated Langmuir kinetic equation (IKL), Langmuir–Freundlich kinetic equation and recently derived fractal-like MOE (f-MOE) and IKL models were compared and used to analyze adsorption kinetic data. New generalization of Langmuir kinetics (gIKL), MOE and f-MOE were used to describe desorption kinetics. Analysis of adsorption and desorption half-times shows simple relation to the size of carbon pores.

Keywords: Adsorption kinetics; Desorption kinetics; Langmuir kinetics; Generalized integrated Langmuir kinetic equation; Mixed order kinetic equation; Fractal-like kinetics; Intraparticle diffusion model; Pore diffusion model

Adsorption and diffusion of nitrogen, methane and carbon dioxide in aluminophosphate molecular sieve AlPO₄-11 by J. A. Delgado; V. I. Águeda; M. A. Uguina; J. L. Sotelo; Paz Fernández (pp. 407-422).

The knowledge about the adsorption and diffusion properties (specially about diffusion) of aluminophosphate molecular sieves is very scarce in the literature. These materials offer interesting properties as adsorbents as they have a polar framework and do not contain charge-balancing cations. In this work, the adsorption isotherms of nitrogen, methane and carbon dioxide over an AlPO₄-11 sample synthesized in our laboratories have been measured with a volumetric method at 25, 35, 50 and 65 °C over a pressure range up to 110 kPa. The adsorption capacities of each gas are determined by the strength of interaction with the pore surface (carbon dioxide > methane > nitrogen). The equilibrium selectivity to carbon dioxide is quite high with respect to other adsorbents without cations due to the polarity of the aluminophosphate framework. The adsorption Henry’s law constants and diffusion time constants of nitrogen, methane and carbon dioxide in the synthesized AlPO₄-11 material have been measured from pulse experiments. A pressure swing adsorption (PSA) process for recovering methane from a carbon dioxide/methane mixture (resembling biogas) has been designed using a dynamic model where the measured adsorption equilibrium and kinetic information has been incorporated. The simulation results show that the proposed process could be simpler than other PSA processes for biogas upgrading based on cation-containing molecular sieves such as 13X zeolite, as it can treat the biogas at atmospheric pressure, and it requires a lower pressure ratio, to produce high purity methane with high recovery.

Keywords: Carbon dioxide; Methane; Nitrogen; AlPO₄-11; Adsorption; Diffusion; Pressure swing adsorption

Adsorption of Ni(II) from model solutions using co-precipitated inorganic oxides by Filip Ciesielczyk; Przemysław Bartczak; Karolina Wieszczycka; Katarzyna Siwińska-Stefańska; Magdalena Nowacka; Teofil Jesionowski (pp. 423-434).

The aim of this work was to obtain an inorganic oxide system containing silica and magnesium oxide, and characterized by specific physicochemical properties, in particular well-defined adsorption parameters. The preparation process was carried out according to a co-precipitation method using solutions of sodium silicate and selected inorganic magnesium salt. The oxide system obtained (MgO·SiO₂) was used as a support (adsorbent) of nickel(II) ions, whose precursors were model solutions of nitrates. The effectiveness of the adsorption process was evaluated using many different analytical techniques, including atomic absorption spectroscopy, energy dispersive X-ray spectroscopy and equivalent point titration. Moreover the stability of adsorbent/adsorbate bonding was estimated. The oxide systems—adsorbents—used in the process were also analyzed according to their physicochemical properties, especially changes in adsorption parameters. The last part of the study involved evaluation of the kinetics of the adsorption process depending on time and the pH of the reaction system.

Keywords: Inorganic oxide adsorbent; Nickel(II) ions; Adsorption; Atomic absorption spectroscopy; Energy dispersive X-ray spectroscopy; Equivalent point titration

Adsorption of Triton X-100 and cetyltrimethylammonium bromide mixture with ethanol at nylon-6–solution interface with regard to nylon-6 wettability: I. The effect of adsorption on critical surface tension of nylon-6 wetting by Magdalena Bielawska; Bronisław Jańczuk; Anna Zdziennicka (pp. 435-444).

The contact angle measurements of the aqueous solutions of p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (TX-100) and cetyltrimethylammonium bromide (CTAB) mixture with ethanol on nylon-6 were made in the range of the total concentration of CTAB and TX-100 mixture from 1 × 10⁻⁶ to 1 × 10⁻³ M and ethanol from 0 to 17.13 M. In the CTAB and TX-100 mixture the mole fraction of TX-100 was equal to 0; 0.2; 0.4; 0.6; 0.8 and 1. On the basis of the obtained results, the critical surface tension of nylon-6 wetting was determined from the dependence of cosine of contact angle and the adhesion tension as a function of the surface tension of the solution. This tension was compared to the components and parameters of nylon-6 surface tension taken from literature and discussed in the light of the surface excess concentration of the surface active agents at the nylon-6–solution interface calculated from the Lucassen-Reynders equation and the Gibbs isotherm.

Keywords: Nylon-6; Triton X-100; CTAB; Ethanol; Wetting; Contact angle; Gibbs surface excess concentration

Adsorption of Triton X-100 and cetyltrimethylammonium bromide mixture with ethanol at nylon-6–solution interface with regard to nylon-6 wettability: II. Work of adhesion and activity of surfactants at interfaces by Magdalena Bielawska; Bronisław Jańczuk; Anna Zdziennicka (pp. 445-453).

On the basis of the values of the surface tension of the aqueous solutions of the Triton X-100 and CTAB mixture with ethanol, the surface tension of nylon-6 and the nylon-6–solution interfacial tension, the activity of the surfactant mixture and ethanol at the nylon-6–solution interface was calculated and compared to that at the solution–air one. For these calculations, the Sprow and Prausnitz equation was applied. The obtained values of the activity were used for the calculations of the work of adhesion of the solution to the polymer surface. The values of the work of adhesion obtained in this way were compared to those determined from the Young–Dupre equation by using the contact angle values of the aqueous solutions of the TX-100 and CTAB mixture with ethanol measured on the nylon-6 surface. The changes of the work of adhesion determined from the Young–Dupre equation were also considered as a function of the surface tension of the solution, its polar component and the interfacial interaction parameter.

Keywords: Contact angle; Wettability; Critical surface tension of solid wetting; Surface tension; Surfactants; Adhesion work; Nylon-6

Coordination of extraframework Li⁺ cation in the MCM-22 and MCM-36 zeolite: FTIR study of CO adsorbed by Roman Bulánek; Monika Kolářová; Pavla Chlubná; Jiří Čejka (pp. 455-463).

Nature and population of Li⁺ cationic sites in MCM-22 zeolite and its pillared form (MCM-36) were investigated by means of adsorption of CO as a probe molecule. CO stretching frequency and adsorption heat were measured by FTIR spectroscopy and adsorption microcalorimetry. Intrazeolitic carbonyl complexes on Li⁺ cations in MCM-22 and MCM-36 are characterized by two main vibrational bands at 2,195 and 2,188 cm⁻¹. Band at higher wavenumbers is ascribed to carbonyls on Li⁺ ions coordinated only to two oxygen atoms at the intersection of 10-ring channels and interacting with CO molecule by energy around 45 kJ mol⁻¹. Band at 2,188 cm⁻¹ was assigned to the carbonyls on Li⁺ cations located on top of 5 or 6-rings on the channel walls and coordinated to three or four oxygen atoms, interacting with CO molecule by energy 33–36 kJ mol⁻¹. Effect of pillaring and layered form of zeolite on nature and population of Li⁺ cationic sites is also discussed, as well as the formation of dicarbonyl complexes.

Keywords: FTIR; CO; Adsorption microcalorimetry; MCM-22; MCM-36

Magnetite nanoparticles for removal of heavy metals from aqueous solutions: synthesis and characterization by Liliana Giraldo; Alessandro Erto; Juan Carlos Moreno-Piraján (pp. 465-474).

Fe₃O₄ magnetic nanoparticles were synthesized by co-precipitation method. The structural characterization showed an average nanoparticle size of 8 nm. The synthesized Fe₃O₄ nanoparticles were tested for the treatment of synthetic aqueous solutions contaminated by metal ions, i.e. Pb(II), Cu(II), Zn(II) and Mn(II). Experimental results show that the adsorption capacity of Fe₃O₄ nanoparticles is maximum for Pb(II) and minimum for Mn(II), likely due to a different electrostatic attraction between heavy metal cations and negatively charged adsorption sites, mainly related to the hydrated ionic radii of the investigated heavy metals. Various factors influencing the adsorption of metal ions, e.g., pH, temperature, and contacting time were investigated to optimize the operating condition for the use of Fe₃O₄ nanoparticles as adsorbent. The experimental results indicated that the adsorption is strongly influenced by pH and temperature, the effect depending on the different metal ion considered.

Keywords: Magnetite; Nanoparticles; Isotherms; Metal ions

Standard nitrogen adsorption data for α-alumina and their use for characterization of mesoporous alumina-based materials by Mietek Jaroniec; Pasquale F. Fulvio (pp. 475-481).

Nitrogen adsorption isotherm measured at −196 °C for a macroporous α-alumina (α-Al₂O₃) is reported. This isotherm is compared with the previously reported adsorption data measured on LiChrospher 1000 silica and with available reference isotherms measured at moderate and high relative pressures on macroporous aluminas. The isotherm reported in this work for α-Al₂O₃ and that recorded previously on LiChrospher 1000 silica were used as reference data for adsorption characterization of ordered and disordered mesoporous aluminas by α s-plot analysis and pore size analysis. It is shown that both reference isotherms provide almost identical adsorption characteristics of the aforementioned mesoporous aluminas, indicating that the available reference data for the silica surface are also suitable for adsorption analysis of alumina-based materials.

Keywords: Nitrogen adsorption; Mesoporous alumina; Standard adsorption data; α s-plot analysis; Porosity

Immobilization of multifunctional silsesquioxane cage on precipitated silica supports by K. Szwarc-Rzepka; B. Marciniec; T. Jesionowski (pp. 483-494).

Synthesis of octakis({3-glycidoxypropyl}dimethylsiloxy) octasilsesquioxane (G-POSS) was carried out based on a reaction involving the hydrosilylation of allyl glycidyl ether with octakis(dimethylsiloxy) octasilsesquioxane, using Karstedt’s catalyst and toluene. SiO₂/POSS hybrid systems were obtained via a method of immobilization by evaporation of the solvent, using hydrated or spherical silica obtained by precipitation in an aqueous or emulsion environment. The surface of the SiO₂ was modified using octakis({3-glycidoxypropyl}dimethylsiloxy) octasilsesquioxane (G-POSS). The effectiveness of the modification of the obtained hybrid materials was verified using Fourier transform infrared spectroscopy and nuclear magnetic resonance (²⁹Si and ¹³C CP MAS NMR). The tests showed that the interactions between the silica support and the modifier are of the nature of chemical adsorption. In addition a mechanism was proposed for the interactions between silica and oligosilsesquioxane. To test the final effect, the hybrid systems were subjected to morphological evaluation (transmission electron microscopy). Parameters of porous structure of the products were also determined: the specific surface area, pore diameter and pore volume. Thermal stability was tested for the pure silsesquioxane cage, the initial silica supports and the resulting systems. Elemental analysis was also carried out to determine the effect of surface modification on the degree of coverage with a particular POSS compound.

Keywords: Multifunctional silsesquioxane cage; Silica; Immobilization; Functionalization; Chemisorption

Devil’s staircase behavior of a dimer adsorption model by V. F. Fefelov; V. A. Gorbunov; A. V. Myshlyavtsev; M. D. Myshlyavtseva; S. S. Akimenko (pp. 495-499).

We have constructed the simple two-dimensional adsorption model with short range non-competing interactions which demonstrates devil’s staircase of phase transitions. The main factor which leads to the appearance of infinite amount of ordered structures in our model is two competing forms of adsorption. The ground state properties of the model have been analyzed.

Keywords: Devil’s staircase; Dimer adsorption; Phase transitions; Ground state

Effects of carbon nanotube functionalization on the agglomeration and sintering of supported Pd nanoparticles by Róbert Puskás; Ákos Kukovecz; Zoltán Kónya (pp. 501-508).

The size of carbon nanotube supported Pd and PdO nanoparticles was investigated on oxidatively functionalized multiwall carbon nanotubes. All samples were characterized by transmission electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy and Raman spectroscopy. The average particle diameter calculated from TEM image analysis was found to be inversely proportional with the duration of the oxidation in nitric acid. Crystallite sizes determined from XRD patterns confirmed this general tendency.

Keywords: Carbon nanotube; Functionalization; Palladium nanoparticle; Size dependence

Phase behavior of attractive k-mers on two-dimensional lattices: a study from quasi-chemical approximation by P. Longone; M. Dávila; J. L. Riccardo; A. J. Ramirez-Pastor (pp. 509-519).

The phase behavior of attractive linear rigid k-mers on two-dimensional lattices was studied by theoretical and simulation calculations in the framework of the lattice-gas model. Combining (i) the analytical expression for the partition function of non-interacting k-mers, and (ii) a generalization of the classical quasi-chemical approximation (QCA) in which the adsorbate can occupy more than one adsorption site, the main thermodynamic functions of the system were explicitly obtained. It was found that, for temperatures below a certain condensation temperature, the system undergoes a first-order phase transition which is observed as a clear discontinuity in the adsorption isotherms. The transition was studied in detail by calculating the temperature–density phase diagrams. Comparisons with analytical data from Bragg–Williams approximation and Monte Carlo simulations were performed in order to test the validity of the theoretical model. The results obtained allowed us not only to analyze the effect of introducing the lateral interactions by following the configuration-counting procedure of the QCA, but also to discuss the consequences of choosing the configurational factor associated to adsorption of non-interacting k-mers from different models developed to treat the multisite occupancy adsorption problem.

Keywords: Multisite occupancy adsorption; Phase transitions; Quasi-chemical approximation

NO₂ removal on adsorbents prepared from coffee industry waste materials by Piotr Nowicki; Paulina Skibiszewska; Robert Pietrzak (pp. 521-528).

A technology for obtaining carbonaceous adsorbents by physical and chemical activation of waste materials from coffee industry is described. The effect of pyrolysis temperature and type of activation procedure on the textural parameters, acid–base character of the surface and sorption properties of activated carbons has been tested. The resulting carbons were characterized by low-temperature nitrogen sorption, determination of pH and the number of surface oxygen groups. The sorption properties of the activated carbons obtained were characterized by evaluation of nitrogen dioxide adsorption in dry and wet conditions. The final products were adsorbents of specific surface area ranging from 5 to 2,076 m²/g and pore volume from 0.03 to 1.25 cm³/g, showing very diverse acidic–basic character of the surface. The results obtained in our study have proved that a suitable choice of the pyrolysis and activation procedure for coffee industry wastes permits production of adsorbents with high sorption capacity of nitrogen dioxide, reaching to 44.5 and 84.1 mg NO₂/g in dry and wet conditions, respectively.

Keywords: Activated carbon; Industrial waste materials; Chemical/physical activation; Nitrogen dioxide adsorption/reduction

What can positronium tell us about adsorption? by Agnieszka Kierys; Radosław Zaleski; Maciej Tydda; Jacek Goworek (pp. 529-535).

The condensation and evaporation of n-heptane at 298 K in mesopores of silica material obtained by the polymer templating method have been studied by PALS measurements. It is demonstrated that the ortho-positronium lifetimes and intensities provide valuable information on pore filling and emptying which are not accessible from a conventional adsorption experiment. The results confirm the specific adsorption mechanism of n-heptane in pores with narrow openings (ink-bottle shape) which is different from that known for other pore geometries. The results from PALS experiment are compared to those derived from the conventional n-heptane and nitrogen adsorption data.

Keywords: Silica gel; Positron annihilation lifetime spectroscopy (PALS); N-heptane adsorption

Application of quasi-equilibrated thermodesorption of hexane and cyclohexane for characterization of porosity of zeolites and ordered mesoporous silicas by Wacław Makowski; Maria Mańko; Anna Dudek; Kinga Mlekodaj (pp. 537-544).

Quasi equilibrated temperature programmed desorption and adsorption (QE-TPDA) of hexane and cyclohexane was applied for characterization of zeolites 5A, ZSM-5, 13X, Y, NaMOR and ordered mesoporous silicas MCM-41, MCM-41/TMB, SBA-15 and HMS. Similar QE-TPDA profiles of hexane and cyclohexane with a single desorption maximum were observed for the wide pore zeolites. No adsorption of cyclohexane for zeolite 5A and a single desorption maximum for ZSM-5 were found, while two-step desorption profiles of hexane were observed for these zeolites. Similar values of the adsorption enthalpy and entropy of hexane and cyclohexane were obtained by fitting the Langmuir model functions for the zeolites X and Y. For NaMOR and ZSM-5 larger differences in these parameters were found. A single desorption peak found at low temperatures in the QE-TPDA profiles of hexane and cyclohexane for the studied silicas was attributed to the multilayered adsorption on their mesopore surface. The adsorption isobars calculated from the thermodesorption profiles were fitted with the BET function. This way values of the specific surface area and the adsorption heat were calculated. Additionally values of the initial heat of adsorption were found by fitting the Henry’s law to the high-temperature sections of the linearized isobars. The largest deviations from the BET and Henry functions and the largest values of the adsorption heats found for SBA-15 indicated the greatest heterogeneity of the adsorption sites on its surface.

Keywords: Hexane; Cyclohexane; Adsorption heat; Zeolite; Mesoporous silica; Surface heterogeneity

A geometrical model of random porous structures to adsorption calculations by Jan T. Duda; Janina Milewska-Duda; Mirosław Kwiatkowski; Magda Ziółkowska (pp. 545-555).

This paper describes a new approach to identification of random porous structures (e.g. present in cheap natural adsorbents, active carbons). It comes from a clustering based description of adsorption process assuming an exponential distribution of adsorbate stack size (the LBET model), combined with the new consistent mathematical relationships between the pore geometry, adsorption isotherm parameters and physical properties of adsorptive. The newly derived formulae are discussed, and results of their application to analysis of an active carbon structure are shown.

Keywords: Adsorbents; Micropores; Isotherms; Models; Numerical analysis

Enhanced and suppressed effects of ionic liquid on the photocatalytic activity of TiO₂ by Lifang Qi; Jiaguo Yu; Mietek Jaroniec (pp. 557-561).

The effects of a room temperature ionic liquid, 1-butyl-3-methylimidazolium terafluoroborate ([Bmim]BF₄), on the photocatalytic performance of Degussa P25 TiO₂ were investigated. Also, the photocatalysis mechanism was systematically analyzed by conducting different reactive radical trapping experiments. The results showed that photogenerated electrons were the main reactive species involved in the photocatalytic degradation of methyl orange (MO), while •OH radicals and photogenerated holes played an important role in the photocatalytic decomposition of rhodamine B (RhB). The addition of ionic liquid (IL) could slightly enhance the photocatalytic degradation rate of MO because adsorption of [Bmim]⁺ ions on the TiO₂ surface not only enhanced traping and transfer of photogenerated electrons, but also facilitated adsorption of negatively charged MO. On the contrary, IL suppressed the degradation rate of RhB because [Bmim]⁺ on the TiO₂ surface not only hindered the access of positively charged RhB to TiO₂, but also restricted the diffusion of positively charged holes to the TiO₂/solution interface.

Keywords: Titania (TiO₂); Photocatalytic activity; Ionic liquid; Adsorption

Organic acid-assisted soft-templating synthesis of ordered mesoporous carbons by Jerzy Choma; Katarzyna Jedynak; Michal Marszewski; Mietek Jaroniec (pp. 563-569).

A series of soft-templated ordered mesoporous carbons (OMCs) was synthesized by using resorcinol and formaldehyde as carbon precursors, triblock copolymer Pluronic F127 as a soft-template, and an organic acid (acetic, benzoic, citric, oxalic, or succinic) as a polymerization reaction catalyst. The aforementioned organic acids were strong enough to facilitate the formation of ordered mesophases by the block copolymer template used and to catalyze the polymerization reaction of resorcinol and formaldehyde in this template. The use of weak organic acids instead of strong inorganic acids such as HCl eliminated inorganic anions from the reaction environment and resulted in high surface area OMCs. Basically, the resulting carbons showed the surface areas and pore volumes comparable to those reported for the carbons prepared under similar conditions but in the presence of strong inorganic acids. Electron microscopy analysis proved the presence of ordered mesopores, whereas thermogravimetric analysis showed a good thermal stability of these carbons.

Keywords: Adsorption properties; Soft-templating synthesis; Mesoporous carbons; Organic acid-assisted synthesis; Block copolymers

Adsorption of triangular-shaped molecules with directional nearest-neighbor interactions on a triangular lattice by V. A. Gorbunov; S. S. Akimenko; A. V. Myshlyavtsev; V. F. Fefelov; M. D. Myshlyavtseva (pp. 571-580).

Using Monte Carlo and transfer-matrix methods the lattice gas model of adsorption of triangular-shaped molecules on a triangular lattice is studied. The constructed model takes into account the directionality of pairwise nearest-neighbor interactions between the adsorbed molecules. It is shown that a predominant character of "tip-to-tip" attractive interactions w ₁ always leads to the formation of the honeycomb structure in the adsorption monolayer with local density ρ = 0.66(6). While, the values of "side-to-side" w ₂ and "tip-to-side" w ₃ interactions define the structure of close-packed phase. Depending on the values of the interactions the close-packed phase may have: (a) completely disordered structure; (b) frustrated honeycomb structure which is formed by Langmuir like adsorption onto 2D pores of the honeycomb structure; (c) ordered close-packed structure consisted of the molecules which all have the same orientation relative to each other and relative to the surface.

Keywords: Lattice gas model; Trimesic acid self-assembly; Molecular porous network Monte Carlo; Transfer-matrix

Comparison of ordered mesoporous materials sorption properties towards amino acids by Joanna Goscianska; Anna Olejnik; Robert Pietrzak (pp. 581-588).

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.

Keywords: Adsorption of l-phenylalanine; l-histidine; Amino acids; Mesoporous carbons; Furfuryl alcohol

Amino-functionalized pore-expanded SBA-15 for CO₂ adsorption by A. Olea; E. S. Sanz-Pérez; A. Arencibia; R. Sanz; G. Calleja (pp. 589-600).

The adsorption of CO₂ on pore-expanded SBA-15 mesostructured silica functionalized with amino groups was studied. The synthesis of conventional SBA-15 was modified to obtain pore-expanded materials, with pore diameters from 11 to 15 nm. Post-synthesis functionalization treatments were carried out by grafting with diethylenetriamine (DT) and by impregnation with tetraethylenepentamine (TEPA) and polyethyleneimine (PEI). The adsorbents were characterized by X-ray diffraction, N₂ adsorption–desorption at 77 K, elemental analysis and Transmission Electron Microscopy. CO₂ capture was studied by using a volumetric adsorption technique at 45 °C. Consecutive adsorption–desorption experiments were also conducted to check the cyclic behaviour of adsorbents in CO₂ capture. An improvement in CO₂ adsorption capacity and efficiency of amino groups was found for pore-expanded SBA-15 impregnated materials in comparison with their counterparts prepared from conventional SBA-15 with smaller pore size. PEI and TEPA-based adsorbents reached significant CO₂ uptakes at 45 °C and 1 bar (138 and 164 mg CO₂/g, respectively), with high amine efficiencies (0.33 and 0.37 mol CO₂/mol N), due to the positive effect of the larger pore diameter in the diffusion and accessibility of organic groups. Pore-expanded SBA-15 samples grafted with DT and impregnated with PEI showed a good stability after several adsorption–desorption cycles of pure CO₂. PEI-impregnated adsorbent was tested in a fixed bed reactor with a diluted gas mixture containing 15 % CO₂, 5 % O₂, 80 % Ar and water (45 °C, 1 bar). A noteworthy adsorption capacity of 171 mg CO₂/g was obtained in these conditions, which simulate flue gas after the desulphurization step in a thermal power plant.

Keywords: Pore-expanded SBA-15; Amino-functionalization; Diethylenetriamine; Polyethyleneimine; Tetraethylenepentamine; CO₂ capture

Effect of the pore geometry in the characterization of the pore size distribution of activated carbons by J. P. Toso; J. C. A. Oliveira; D. A. Soares Maia; V. Cornette; R. H. López; D. C. S. Azevedo; G. Zgrablich (pp. 601-609).

In this work, the characterization of Activated Carbons (AC) by using the independent pore models is discussed, with special emphasis on the issue of how the assumed pore geometry can affect the resulting Pore Size Distribution (rPSD) and on the problem of the unicity of the PSD when different probe molecules are used in adsorption experiments. A theoretical test was performed using virtual solids based in the so-called Mixed Geometry Model (MGM) (Azevedo et al. 2010). The MGM uses a kernel of adsorption isotherms generated by GCMC for different pore sizes and two pore geometries: slit and triangular. The adsorption isotherms of a virtual MGM solid were fitted with both the traditional Slit Geometry Model (SGM) and the Mixed Geometry Model (MGM). It is demonstrated that, by assuming a different pore geometry model from that of the real sample, different PSDs may be obtained by fitting adsorption isotherms of different probe gases. Finally, experimental results are shown which both point toward the MGM as an acceptable extension of the SGM and confirm that the MGM is a closer representation of the actual porous structure of most activated carbons.

Keywords: Activated carbon; Independent pores model; Monte carlo simulation; Unicity of PSD

Effects of surface heterogeneity of carbon nanotubes in adsorption of colloid nanoparticles studied by means of computer simulations by Tomasz Panczyk; Wladyslaw Rudzinski (pp. 611-618).

This work deals with a construction of an implicit solvent model which can be used in molecular dynamics simulations of systems comprising colloid nanoparticles and carbon nanotubes. Such systems, due to finite sizes of both components, cannot be accurately approximated by a smaller slab geometry and thus represent a particularly difficult case in terms of computer simulations. Adsorption of large colloid nanoparticles on the surfaces of carbon nanotubes were studied and we determined the adsorption energy profiles of the nanoparticles on the carbon nanotubes surfaces. We also determined the adsorption isotherms which help to understand a preferred location of the nanoparticles on the nanotubes surfaces.

Keywords: Carbon nanotube; Colloid nanoparticle; Implicit solvent model; Molecular dynamics; Adsorption

TiO₂-assisted photocatalytic degradation of diclofenac, metoprolol, estrone and chloramphenicol as endocrine disruptors in water by Bożena Czech; Katarzyna Rubinowska (pp. 619-630).

The photocatalytic oxidation of diclofenac, metoprolol, estrone and chloramphenicol was tested in the tube reactor using different commercially available TiO₂. The photocatalysts were characterized using BET, XRD and SEM. The studied photocatalysts differed in S_BET, pore volume and rutile presence. It was observed that generally anatase TiO₂ possessed the highest activity in the photocatalytic oxidation of diclofenac, chloramphenicol and estrone. The presence of rutile enhanced the photooxidation of metoprolol. In case of the other pollutants, however, rutile diminished the photooxidation efficiency. The most effective in the reduction of the COD parameter of treated water was anatase with 21 nm crystals. The photooxidation of all studied pollutants can be described by the pseudo-first order kinetics with the values ranging from 0.46 × 10⁻² min⁻¹ in case of estrone removal over Tytanpol (Z.A. Police, Poland) to 1.87 × 10⁻² min⁻¹ for the removal of chloramphenicol over TiO₂ 21 nm (Sigma-Aldrich). The highest initial reaction rates were obtained for metoprolol removal over TiO₂ 21 nm (Sigma-Aldrich) 1.9 × 10⁻⁶ mol dm³ min⁻¹ being three times higher than that determined for estrone photocatalytic oxidation over TiO₂ (Sigma-Aldrich).

Keywords: Photocatalysis; TiO₂ ; PPCPs; AOPs; EDCs

Capillary condensation in mesoporous silica with surface roughness by Hideki Tanaka; Tatsumasa Hiratsuka; Natsumi Nishiyama; Kengo Mori; Minoru T. Miyahara (pp. 631-641).

We construct an atomistic silica pore model mimicking templated mesoporous silica MCM-41, which has molecular-level surface roughness, with the aid of the electron density profile (EDP) of MCM-41 obtained from X-ray diffraction data. Then, we present the GCMC simulations of argon adsorption on our atomistic silica pore models for two different MCM-41 samples at 75, 80, and 87 K, and the results are compared with the experimental adsorption data. We demonstrate that accurate molecular modeling of the pore structure of MCM-41 by using the experimental EDP allows the prediction of experimental capillary evaporation pressures at all investigated temperatures. The experimental desorption branches of the two MCM-41 samples are in good agreement with equilibrium vapor–liquid transition pressures from the simulations, which suggests that the experimental desorption branch for the open-ended cylindrical pores is in thermodynamic equilibrium.

Keywords: MCM-41; Electron density profile; Surface roughness; Capillary condensation; Molecular simulation

Supercritical hydrogen adsorption in nanostructured solids with hydrogen density variation in pores by Jessica E. Sharpe; Nuno Bimbo; Valeska P. Ting; Andrew D. Burrows; Dongmei Jiang; Timothy J. Mays (pp. 643-652).

Experimental excess isotherms for the adsorption of gases in porous solids may be represented by mathematical models that incorporate the total amount of gas within a pore, a quantity which cannot easily be found experimentally but which is important for calculations for many applications, including adsorptive storage. A model that is currently used for hydrogen adsorption in porous solids has been improved to include a more realistic density profile of the gas within the pore, and allows calculation of the total amount of adsorbent. A comparison has been made between different Type I isotherm equations embedded in the model, by examining the quality of the fits to hydrogen isotherms for six different nanoporous materials. A new Type I isotherm equation which has not previously been reported in the literature, the Unilan-b equation, has been derived and has also been included in this comparison study. These results indicate that while some Type I isotherm equations fit certain types of materials better than others, the Tόth equation produces the best overall quality of fit and also provides realistic parameter values when used to analyse hydrogen sorption data for a model carbon adsorbent.

Keywords: Hydrogen adsorption; Porous solids; Isotherm equations

The influence of energetic surface heterogeneity on proton desorption during capillary filling of silica nanochannels by W. Piasecki; R. Charmas (pp. 653-658).

We applied the surface complexation model to describe the deprotonation of silica nanochannel walls as a function of pH and ionic strength of filling solution. We took into account energetic heterogeneity of silanol groups. We found that more heterogeneous walls of silica nanochannel will be more charged and can interact more strongly with ionic solutes. The modeling of nanochannels coated with 3-cyanopropydimethylchlorosilane is uncertain because charging mechanism of coated silica should take into account increased autolysis of interfacial water.

Keywords: Silica; Nanochannels; Nanofluidics; Deprotonation; Energetic heterogeneity; Surface complexation

Equilibrium and kinetic modeling of metal ion biosorption: on the ways of model generalization for the case of multicomponent systems by Wojciech Plazinski (pp. 659-666).

The paper is devoted to the problem of multicomponent sorption of metal ions on the algae-based biosorbents. The basic methods of generalization of the single-component adsorption models are reviewed or introduced and commented for both biosorption equilibrium and kinetics. The problem of similarities and difference between the competitive adsorption and the ion-exchange models is discussed and analyzed to state that both these approaches give the same results providing that only equilibrium properties are considered.

Keywords: Modeling; Sorption; Adsorption; Equilibrium; Kinetics; Multicomponent

The balancing of VOC concentration fluctuations by adsorption/desorption process on activated carbon by L. Kuboňová; L. Obalová; L. Skovranek; I. Troppová (pp. 667-673).

Volatile organic compounds (VOCs) are mostly toxic and carcinogenic substances. The technologies for cleaning of exhaust gases containing the constant concentrations of VOCs are commercially available. However, if concentration fluctuations occur in the range of several orders of magnitude, it can cause problems for a subsequent gas cleaning e.g. by thermal or catalytic oxidation. The balancing of VOC concentrations in flue gases can be a great simplification of a subsequent reduction of VOC emissions from sources with time-variable concentrations. Paint shops belong to the important sources of VOCs and are an example of periodic processes with time-variable concentrations of VOCs. One of the main aims was to experimentally determine the conditions, such as the minimal mean residence time, to balance out the fluctuations of inlet VOC concentrations at the laboratory model. After that, the verification of obtained results was applied for a real exhaust gas from a paint shop.

Keywords: Volatile organic compounds; Concentration fluctuations; Balancing; Activated carbon; Adsorption

Removal of lead(II) and zinc(II) ions from aqueous solutions by adsorption onto activated carbon synthesized from watermelon shell and walnut shell by Jonathan Julián Moreno-Barbosa; Catalina López-Velandia; Andrea del Pilar Maldonado; Liliana Giraldo; Juan Carlos Moreno-Piraján (pp. 675-685).

Activated carbons from watermelon shell (GACW) and walnut shell (GACN) were synthesized through chemical activation with phosphoric acid 40 % w/w, as an alternative low-cost adsorbent for the removal of lead(II) and zinc(II) ions from aqueous solutions. The yield of production was 85 and 80 % for GACW and GACN respectively. To compare the differences and similarities between the two activated carbons the following tests were performed: surface and pore width with SEM, nitrogen adsorption isotherms at −196 °C (77 K), IR spectroscopy, TGA, point of zero charge (PZC) and Boehm titration. The GACN has 10 % more surface area (789 m² g⁻¹ for GACN and 710 m² g⁻¹ for GACW) and 13 % more pore volume than GACW. Also, GACN has a better resistance to high temperatures than GACW (the loss of mass at 900 °C was 20 % for GACN, while for GACW was 31 %). The effect of the initial concentration of lead(II) and zinc(II) ions on the adsorption process was studied in a batch process mode. To quantify the adsorption of lead and zinc adsorption isotherms of both metals in aqueous solution were performed for each carbon using analytic technique of atomic absorption. The adsorption isotherm data were better fitted by Langmuir model. Experimental results suggests that one gram of GACW adsorbs more milligrams of lead(II) and zinc(II) than one gram of GACN; it is suggest that the pore distribution is a significant variable in the adsorption process because GACW present mesopores and micropores, while GACN has only micropores. Also, the surface chemistry is an important variable in the adsorption process because GACW presents a lower pH_PZC than GACN (3.05 for GACW and 4.5 for GACN) and the solution’s pH of each metal was adjusted in 4.5, for that it could be suggested that the electrostatic interactions were increased between the ion and the carbon surface.

Keywords: Adsorption from solution; Activated carbon; Watermelon; Walnut; Lead; Zinc

Effect of planetary ball milling process parameters on the nitrogen adsorption properties of multiwall carbon nanotubes by Ibolya Zita Papp; Gábor Kozma; Róbert Puskás; Tímea Simon; Zoltán Kónya; Ákos Kukovecz (pp. 687-694).

The dependence of multiwall carbon nanotube (MWCNT) length distribution and some nitrogen derived morphological descriptors on various planetary ball milling process parameters was investigated. Ball milling was found to cut nanotubes into smaller pieces, narrow their length distribution and increase their specific surface area and surface fractal dimension. Typical length reduction was from 1300 to 200 nm, specific surface area increase from 160 to 340 m²g⁻¹ and surface fractal dimension increase from 2.47 to 2.70. The pore size distribution of pristine MWCNTs exhibited a mesoporous character dominated by intertube channels. A sharp maximum appeared at d = 3.6 nm diameter when the milling power was increased. This increase was attributed to the opening of intratube voids. Processes involving graphitic platelet detachment, tube wall amorphization or carbonaceous debris accumulation appear to play only minor roles under the studied experimental conditions of planetary milling. Control over the morphology of the milled material is best achieved by varying the diameter and the mass ratio of the grinding balls as well as the classical process parameters like disk rotational speed, milling time and number of balls.

Keywords: Carbon nanotube; Ball mill; Nitrogen adsorption; Fractal dimension

Fine tuning the surface acidity of titanate nanostructures by D. Madarász; I. Szenti; L. Nagy; A. Sápi; Á. Kukovecz; Z. Kónya (pp. 695-700).

The effect of protonation on the surface acidic properties of titanate nanowires (TiONWs) was investigated. Nanowires were synthesized by the alkali hydrothermal method which resulted in one dimensional nanostructures of large external surface area and well-defined lamellar interlayer structure. The Na⁺/H⁺ ratio in the structure can be tuned by ion-exchange. Our aim was to characterize the morphology of the as-synthesized nanostructures by HRTEM and SEM measurements and assess their surface acidity using in situ infrared spectroscopic measurements and temperature programmed desorption. It was found that the numbers of Lewis and Brönsted acidic sites in the Na-form and the H-form of the TiONWs is different. The ratio and the nature of acidic sites can be tuned by the ion exchange process. The wire-like morphology and the tunable acidity are features of titanate nanowires that may render them a promising material in various heterogeneous catalytic applications.

Keywords: Titanate nanowires; Surface acidity; Pyridine adsorption; Solid acids

Misleading information on homogeneity and heterogeneity obtained from sorption isotherms by József Kónya; Noémi M. Nagy (pp. 701-707).

In this paper, the applications and the differences among the widely applied sorption isotherms (Langmuir isotherm for adsorption, competitive adsorption, ion exchange, Freundlich isotherm) are shown. The misleading information obtained by the formal applications of the isotherms is demonstrated using a simple mathematical model of homovalent ion exchange on homogeneous surface. This model calculation clearly reveals that when studying surface accumulation processes, the mechanism of the sorption process has to be determined. The correct thermodynamic interpretation of the data of sorption experiments is possible only if the isotherm is adapted to the sorption mechanism. It is emphasized that the regression values of the applied models themselves provide correct information neither on the surface heterogeneity nor the interactions among the sorbed species. The curved shape of an inadequate applied isotherm gives no information about the heterogeneity. In order to study the energy distribution of surface sites, the thermodynamic equations, including isotherms, has to be selected on the basis of sorption mechanism. All variable quantities involved in the given model (concentrations of the competing substances in all phases) have to be measured experimentally and included into the isotherm.

Keywords: Accumulation; Adsorption isotherm; Ion exchange isotherm; Homogeneous surface; Heterogeneous surface

Enhanced sorption of perfluorooctane sulfonate and Cr(VI) on organo montmorillonite: influence of solution pH and uptake mechanism by Qin Zhou; Gang Pan; Wei Shen (pp. 709-715).

An effective sorbent to remove the perfluorooctane sulfonate (PFOS) and hexavalent chromium (Cr(VI)) simultaneously from simulating plating wastewater was prepared in this study. The removal of Cr was pH-dependent. However, PFOS removal on organo-montmorillonites (Mts) was not sensitive to pH changes. The presence of micelles and hemi-micelles resulted in an enhanced PFOS sorption capacity which reached 1,000 mg/g on the hexadecyltrimethylammonium bromide (HDTMAB) modified montmorillonite. The cationic surfactants on organo-Mts were largely responsible to the hydrophobic partition. For Cr(VI), the stable coordination compounds between amido, sulfhydryl groups and HCrO₄ ⁻ were beneficial to its sorption on AET–Mt and AET–HDTMAB–Mt (AET, 2-aminoethanethiol hydrochloride). The result indicated that the AET–HDTMAB–Mt was highly effective for removing both PFOS and Cr(VI) simultaneously, and their sorption capacities reached 890 and 14 mg/g respectively.

Keywords: Perfluorooctane sulfonate (PFOS); Hexavalent chromium; Hydrophobic partition; Electrostatic attraction; Sorption; Simultaneous

Structural and surface heterogeneity of phosphorus-containing polyimide-derived carbons: effect of heat treatment temperature by A. M. Puziy; O. I. Poddubnaya; M. Sobiesiak; B. Gawdzik (pp. 717-722).

Phosphorus-containing carbons have been obtained by carbonization of porous copolymer of 4,4′-bis(maleimidodiphenyl)methane (50 mol%) and divinylbenzene (50 mol%) in presence of phosphoric acid at temperatures 400–1000 °C. Porous structure was analyzed by nitrogen adsorption isotherms while surface chemistry was investigated by potentiometric titration method. It has been shown that carbons obtained at 500–1000 °C are micro-mesoporous with pore sizes of 1–1.1, 2–3 and 5.4 nm. The most developed porosity was achieved at 600 °C reaching BET surface area 890 m²/g and total pore volume 0.45 cm³/g. Carbons obtained by carbonization of polyimide precursor in presence of phosphoric acid showed acidic character with 30–40 % of phosphate surface groups. Maximum total amount of acidic surface groups was achieved at 800 °C reaching 3.2 mmol/g. Assignment of strongly acidic surface groups to phosphates was corroborated by pK value, phosphorus content and thermal gravimetric analysis.

Keywords: Activated carbon; Polyimides; Porous structure; Potentiometric titration; Surface groups

Textural characteristics of sulphided hydrotreatment catalysts prepared using Co–Mo complex compounds by K. A. Leonova; O. V. Klimov; E. Yu. Gerasimov; P. P. Dik; V. Yu. Pereyma; S. V. Budukva; A. S. Noskov (pp. 723-731).

Sulphided Co–Mo catalysts prepared by supporting (CoL)₂[Mo₄(C₆H₅O₇)₂O₁₁]·xH₂O on γ-Al₂O₃ were studied. Pores with diameters less than 40 Å in the catalysts preliminary dried at 120 °C were observed. The volume of these pores is proportional to the amount of carbon-containing decomposition products of the citrate ligands. No narrow pores in preliminary calcined catalysts were observed, whereas a sulphided active component was uniformly distributed in pores with diameters greater than 50 Å, independent of the active-metal concentration. The morphology of the active component particles depends on the conditions of the heat pretreatment. Catalysts that contain particles with an average of 2.1 ± 0.2 layers in a stack and pores with diameters of 60–120 Å are the most active in the hydrotreatment of diesel fuels.

Keywords: Hydrotreating; Localisation of active compound; Micropores

Amorphous and ordered organosilicas functionalized with amine groups as sorbents of platinum (II) ions by Mariusz Barczak; Ryszard Dobrowolski; Joanna Dobrzyńska; Emil Zięba; Andrzej Dąbrowski (pp. 733-744).

Two groups of amine-functionalized organosilicas have been synthesized: amorphous polysiloxane xerogels (APX) and ordered mesoporous organosilicas (OMO) by co-condensation of tetraethoxysilane and appropriate alkoxysilanes: aminopropyltriethoxysilane and N-[3-(trimethoxysilyl)propyl]ethylenediamine. The obtained materials were characterized by sorption measurements, X-ray diffractometry, elemental analysis, transmission electron microscopy, and scanning electron microscopy. The OMO samples have well developed porous structure—the values of specific surface area are in the range 740–840 m²/g. While the APX samples are less porous having the corresponding values in the range 280–520 m²/g. The sizes of the ordered mesopores of OMO are in the range 5.9–6.5 nm while for the APX they are 2.9–12.1 nm indicating structural differences between both groups of the samples. All samples were tested as the sorbents of Pt(II) ions. The influence of various parameters such as pH, contact time, equilibrium concentration on Pt(II) adsorption ability onto prepared adsorbents was studied in detail. Additionally, the effect of chloride concentration on Pt(II) adsorption was investigated. The values of static sorption capacities were in the range of 32–102 mg_Pt(II)/g and 20–139 mg_Pt(II)/g for OMO and APX series, respectively.

Keywords: Sol–gel; Polysiloxanes; Organosilicas; Functionalization; Adsorption; Platinum

Effect of surface functionalities on gas adsorption in microporous carbons: a grand canonical Monte Carlo study by A. Gotzias; E. Tylianakis; G. Froudakis; Th. Steriotis (pp. 745-756).

In an attempt to offer a more realistic picture of adsorption in highly heterogeneous porous systems, such as oxygen functionalized porous carbons, we consider a series of carbon surfaces baring different amounts of oxygen functionalities (hydroxyl and epoxy). These surfaces are used to construct “oxidized” slit pores of varying width and functionality. With the aid of such inhomogeneous structures we study the interaction of Ar (87 K) inside “functionalized” pores and report grand canonical Monte Carlo adsorption simulations results. Based on our simulation data, we discuss the role of chemical heterogeneity on adsorbed/gas phase equilibrium properties such as density, heat of adsorption, and molecular packing within the pores. Comparisons are made with the case of the oxygen–free (completely homogeneous) slit pore models and conclusions on the suitability of Ar based pore size distributions for functionalized porous carbons are drawn.

Keywords: Argon adsorption; Oxidized carbon; Heterogeneity; Confinement; Monte Carlo simulation

Investigation of equilibrium, kinetic, thermodynamic and mechanism of Basic Blue 16 adsorption by montmorillonitic clay by Ahmet Günay; Bahri Ersoy; Sedef Dikmen; Atilla Evcin (pp. 757-768).

The adsorption of a cationic dye, Basic Blue 16 (BB16), by montmorillonitic clay was studied in detail. Changes in the molecular structure during adsorption were analyzed by FTIR spectroscopy. BB16 adsorption onto the clay mainly results from hydrogen bonding between OH and NH₂ groups of dye molecules and OH groups of clay and electrostatic interaction between the negatively charged clay surface and cationic dye. The montmorillonitic clay dose had an inverse effect on the adsorption performance, while the highest dye removal was 305 mg/g at pH 3.6. An increase in temperature and dye concentration positively enhanced the adsorption capacity of the montmorillonitic clay. Temperature had no effect on the adsorption at a dye concentration less than 500 mg/L, while dye adsorption was positively enhanced at elevated dye concentrations. Three-parameter equations provided higher better fitting than two-parameter equations while the Freundlich model had the highest correlation coefficient and the lowest error values with experimental data. The BB16 adsorption was well followed by pseudo-second order model and the rate of adsorption process was controlled by surface and intraparticle diffusion. Thermodynamic evaluations revealed that the adsorption process was spontaneous and endothermic, while the randomness increased during adsorption. Experimental results indicate that montmorillonitic clay from Eskisehir is a promising adsorbent for the removal of cationic dye molecules from aqueous solutions.

Keywords: Montmorillonitic clay; Basic dye; Isotherm; Kinetic; Thermodynamic parameters

Laws and mechanism of adsorption of cations by different ion-exchange forms of silica gel by Sandor Barany; Vladimir Strelko (pp. 769-776).

Using radioactive tracer method, the regularities of adsorption of over 30 mono-, di- and trivalent cations including transition metal and lanthanide ions on the H, Ca- and Al-forms of silica gel are established. It has been shown that the affinity of cations of the same charge to the silica gel surface depends both on the nature of the adsorbing ion and the nature of exchangeable cation on the surface. Adsorption of alkali earth metal ions on the Ca-form of silica gel increases with a decrease of their radius i.e. an inversion of the sequence of adsorption compared to H- or Al-form of this adsorbent or polymeric cation-exchange resins takes place. For lanthanide ions the sequence of adsorption is the same for all ion-exchange forms of the silica gel studied, namely, an increase of adsorption with a decrease of their crystallographic radius, i.e. from La ³⁺ to Lu ³⁺ takes place. The laws observed are explained by taking into account the fact that adsorption of cations by silica gel is determined by both electrostatic interactions and additional covalent/donor–acceptor interactions between the surface and cations. The latter is due to formation of π-bonds between the electron pair in surface oxygen and vacant p-, d- or f-orbital of adsorbing cations.

Keywords: Silica gel; H-, Ca-and Al-forms; Mono-, di- and trivalent cations; Radioactive tracers; Adsorption; Laws; Mechanism; Surface bonds

Carbon slit pore model incorporating surface energetical heterogeneity and geometrical corrugation by Jacek Jagiello; James P. Olivier (pp. 777-783).

In our recent paper (Jagiello and Olivier, Carbon 55:70–80, 2013) we considered introducing energetical heterogeneity (EH) and geometrical corrugation (GC) to the pore walls of the standard carbon slit pore model. We treated these two effects independently and we found that each of them provides significant improvement to the carbon model. The present work is a continuation of the previous one, as we include both effects in one comprehensive model. The existing standard slit pore model widely used for the characterization of activated carbons assumes graphite-like energetically uniform pore walls. As a result of this assumption adsorption isotherms calculated by the non-local density functional theory (NLDFT) do not fit accurately the experimental N₂ data measured for real activated carbons. Assuming a graphene-based structure for activated carbons and using a two-dimensional-NLDFT treatment of the fluid density in the pores we present energetically heterogeneous and geometrically corrugated (EH–GC) surface model for carbon pores. Some parameters of the model were obtained by fitting the model to the reference adsorption data for non-graphitized carbon black. For testing, we applied the new model to the pore size analysis of porous carbons that had given poor results when analyzed using the standard slit pore model. We obtained an excellent fit of the new model to the experimental data and we found that the typical artifacts of the standard model were eliminated.

Keywords: Characterization of porous carbons; Pore size distribution; Non-local density functional theory; Modification of the standard carbon slit pore model

Porosity of closed carbon nanotubes compressed using hydraulic pressure by Piotr A. Gauden; Artur P. Terzyk; Sylwester Furmaniak; Marek Wiśniewski; Piotr Kowalczyk; Agnieszka Bielicka; Wojciech Zieliński (pp. 785-793).

Experimental data of nitrogen adsorption (T = 77.3 K) from gaseous phase measured on commercial closed carbon nanotubes are presented. Additionally, we show the results of N₂ adsorption on compressed (using hydraulic press) CNTs. In order to explain the experimental observations the results of GCMC simulations of N₂ adsorption on isolated or bundled multi-walled closed nanotubes (four models of bundles) are discussed. We show that the changes of the experimental adsorption isotherms are related to the compression of the investigated adsorbents. They are qualitatively similar to the theoretical observations. Taking into account all results it is concluded that in the “architecture” of nanotubes very important role has been played by isolated nanotubes.

Keywords: Carbon nanotubes; Adsorption from gaseous phase; Nitrogen; GCMC simulations; Porosity

Relative stability of icosahedral and cuboctahedral metallic nanoparticles by A. V. Myshlyavtsev; P. V. Stishenko (pp. 795-801).

The size and form of metallic nanoparticles (NPs) significantly affects their adsorptive, chemical, and catalytic activity. One of the most interesting nanoscale size effects is the transition from icosahedral to octahedral forms with growth in the NP size. We compared the stability of icosahedral, decahedral and cuboctahedral NPs made from eight metals Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au using the local optimization of total energy, which was computed from the tight-binding second moment approximation and quantum Sutton–Chen potentials. The obtained results predicted that the icosahedral form would be most stable for Ni, and least stable for Au. For Rh, and especially for Ir, a strong dependency of the stability of the different forms on the NP size was revealed.

Keywords: Nanoparticles; Icosahedral; Cuboctahedral; Energy minimization

A hydrogen sorption study on a Pd-doped CMK-3 type ordered mesoporous carbon by D. Giasafaki; G. Charalambopoulou; A. Bourlinos; A. Stubos; D. Gournis; Th. Steriotis (pp. 803-811).

An ordered mesoporous carbon of CMK-3 type was prepared and modified by metal doping with Pd nanoparticles. The hydrogen sorption performance of the pristine and composite materials was studied at different temperature and pressure conditions in order to provide insight into the underlying storage mechanism. It was shown that metal doping can lead to enhanced hydrogen storage at 298 K as a result of a weak chemisorption process initiated by the so-called “spillover” effect.

Keywords: Hydrogen storage; Ordered mesoporous carbons; Metal doped carbons; Spillover

Comparative analysis of sorption of small molecule hydrocarbons and polar substances in polish hard coals by Grzegorz Jodłowski; Marta Wójcik (pp. 813-819).

The subject of the article is the thermodynamic analysis of the sorption of aliphatic hydrocarbons in hard coals from polish mines. The analysis is based on a Multisorption model designed for describing small molecule sorption in different types of carbonaceous materials (e.g. hard coals, lignites or active carbons). Experimental isotherms of hydrocarbons: hexane, heptane, octane and benzene, in hard coals of different rank, together with water and methanol vapor isotherms measured at room temperature (25 °C), are taken as comparative data for simulations. Results of the analyses reveal the complicated behavior of linear molecules in the sorption system. The location of molecules on the sorbent surface brings a spectrum of problems associated with the incomplete filling of pores, the coiling up of chains, the formulation of plates or globules, and the blocking of micropores. All these effects have an influence on the level and character of sorption, often in opposing ways. The sorption of small inorganic molecules is taken into account in the objective of achieving a more precise identification of the structure of coal. Semi-simultaneous computations for all types of sorbates have already been carried out.

Keywords: Sorption; Adsorption; Absorption; Modeling; Hard coal; Organic solvent

The role of the cation in the oxygen isotopic exchange in crystalline sulfate salt hydrates by S. Attia; L. Hevroni; A. Danon; D. Meyerstein; J. E. Koresh; Y. Finkelstein (pp. 821-833).

The oxygen isotopic exchange during dehydration and decomposition of five sulfate salt hydrates (CoSO₄·6H₂O, NiSO₄·7H₂O, ZnSO₄·7H₂O, CaSO₄·2H₂O, Li₂SO₄·H₂O) was studied in detail by temperature programmed desorption mass spectrometry (TPD-MS) in a supersonic molecular beam (SMB) inlet mode. Crystals of the ¹⁸O-enriched salts were grown and the detailed desorption steps of the various gaseous products released during dehydration and decomposition of these compounds were recorded. The desorption patterns confirmed the known characteristic stepwise dehydration of these salts, where regardless of the crystalline structure and composition, in all the salts (excluding the Li and Ca sulfates) a major group of n − 1 loosely bounded water of crystallization molecules (out of total of n molecules in the fully hydrated form) are released at adjacent temperatures in a typical low temperature range (<200 °C), while the last, most strongly bounded water molecule, consistently desorbs at relatively higher temperatures (240 < T < 440 °C). Interestingly, it is established that the oxygen isotopic exchange occurs exclusively between that latter, most strongly bound water molecule, and the salt anion. Remarkably, the results point out that the exchange process is mostly of solid-solid nature. Finally, the results point out that the probability of the isotopic exchange increases with the increment in the desorption temperature of the last dehydration step, i.e. with the bond strength in the monohydrate, between the last water molecule of crystallization and the cation.

Keywords: Temperature programmed desorption; ¹⁸O; Isotopic exchange; Water of crystallization; Sulfate hydrate

Direct contact free real-time acquisition of temperature profiles in adsorbent bed during vacuum swing adsorption by Maxim S. Mel’gunov; Artem B. Ayupov; Vladimir B. Fenelonov; Boris G. Vainer (pp. 835-840).

Real-time temperature co-axial profiles in a bed of mesoporous alumosilicate were recorded by means of FPA-based infrared thermography during air drying vacuum swing adsorption cycles. The good correlation between experimentally measured temperature profiles and profiles simulated on the basis of linear driving force model of mass and heat transfer in nonadiabatic regime is observed.

Keywords: Non-isothermal adsorption; Vacuum swing adsorption; FPA-based infrared thermography; Temperature profiles

Determination of the textural characteristics of carbon samples using scanning electronic microscopy images: comparison with mercury porosimetry data by A. C. Alvarez; N. Passé-Coutrin; S. Gaspard (pp. 841-850).

In this paper, scanning electron microscopy (SEM) images of carbon samples were analysed, and some textural characteristics were obtained and compared with those determined using mercury porosimetry data. Fractal dimensions were calculated from both mercury porosimetry and SEM images as methods for characterising the porous distribution (heterogeneity) of the samples. Lacunarity is easily determined from SEM images as a measure of the degree of heterogeneity of a porous surface. A relationship between the lacunarity and the fractal dimensions calculated using both methods is shown. Pore-size distributions were also determined from the analysis of SEM images. We show that the analysis of SEM images is a valuable complement to mercury porosimetry measurements and a useful tool for the characterisation of porous surfaces. This method offers the possibility of evaluating the features of porous materials and comparing the results to those obtained using mercury intrusion analysis.

Keywords: Fractal dimension; Lacunarity; Activated carbons; Scanning electronic microscopy; Pore size; Mercury porosimetry

Physical sorption and thermogravimetry as the methods used to analyze linear polymeric structure by Paweł Mergo; Małgorzata Gil; Wiesław Podkościelny; Marta Worzakowska (pp. 851-859).

An increased interest in polymer optical fibers can be observed in the last years. One of the main problems in the technology of these fibers is achieving good optical and thermal stability of used polymer materials. This paper presents a series of manufactured poly(methyl methacryalte) samples which quality was investigated using the physical sorption and the thermogravimetry methods. Studies were carried out to optimize the composition of the starting mixtures used to obtain proper polymer optical fibers.

Keywords: Optical fibers; Thermogravimetry; Adsorption; Polymer; Technology

Thermodynamic and structural properties of water adsorbed film on MgO (100) ionic surface by J. P. Coulomb; B. Demirdjian; D. Ferry; M. Trabelsi (pp. 861-867).

We have investigated by adsorption isotherms and neutron diffraction measurements, respectively the thermodynamic and structural properties of water physisorbed film on MgO (100) powder. Thanks to a high temperature thermal treatment, under vacuum, our MgO powder samples are characterized by a highly homogeneous (100) MgO surface. We have determined the structure of the (2D) water film physisorbed on such an ionic surface. This one is a commensurate P(2×3) structure which is very similar to the (110) planes of ice-VII. Recall that ice VII, which is stable at very high pressure, is characterized by a quite large density (d = 1.6).

Keywords: Water physisorption; MgO (100) powder; Adsorption isotherms; Neutron diffraction; P(2×3)commensurate structure; Ice-VII; (2D) High density water solid phase

Grand canonical monte carlo modeling of hydrogen adsorption on phosphorus-doped open carbon framework by A. Mohammadhosseini; P. Boulet; B. Kuchta (pp. 869-877).

Mechanism of hydrogen adsorption in high surface area carbon-based porous materials has been studied. Influence of chemical modification of the adsorbing surface has been simulated using grand canonical Monte Carlo method. Special attention has been paid to the competition between increasing the surface of open carbon frameworks and heterogeneous distribution of the energy of adsorption. Additionally, it has been shown that the molecular mass of atoms which substitute carbon atoms is an important factor determining the final hydrogen uptake.

Keywords: Hydrogen adsorption; Carbon-based adsorbents; Polycyclic aromatic hydrocarbons (PAHs); Density functional theory (DFT); Grand-canonical Monte Carlo simulation; Phosphorus

Adsorption kinetics and isotherm parameters of naphthalene onto natural- and chemically modified bentonite from aqueous solutions by E. Mine Öncü Kaya; A. Safa Özcan; Özer Gök; Adnan Özcan (pp. 879-888).

Polycyclic aromatic hydrocarbons (PAHs) have widely been studied and a special concern because of their mutagenic and carcinogenic activities. In this study, natural- and chemically modified-bentonite were characterized by means of N₂ adsorption method, XRD, SEM, FT-IR, elemental and thermal analysis and zeta potential techniques and their adsorption behavior were then investigated toward naphthalene, which is the first member of the PAHs. The effects of various experimental parameters such as pH, contact time and temperature on adsorption were tested in the experiments. The optimum pH values for naphthalene adsorption onto natural bentonite (NB) and hexadecyltrimethylammonium bromide modified bentonite (HB) were found to be as 4.00 and 5.97, respectively. The equilibrium contact time was 60 min for both of the adsorbent. A comparison of the linear and nonlinear method of three widely used kinetic models, which are Lagergren-first order, the pseudo-second-order and Elovich kinetics, and the most popular isotherms, which are Langmuir and Freundlich, were examined to the experimental data of the adsorption of naphthalene onto NB and HB. The kinetic results indicated that the pseudo-second-order kinetic model with high correlation coefficients was more suitable than the other kinetic models e.g. Lagergren first-order and Elovich. All results showed that the modified bentonite can be used as an adsorbent to remove PAHs from aqueous solutions by using adsorption method due to its effectiveness, simplicity and low-cost than the other conventional methods.

Keywords: Adsorption; Bentonite; Characterization; Naphthalene; Modification

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Adsorption: Journal of the International Adsorption Society (v.19, #2-4)

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Adsorption: Journal of the International Adsorption Society (v.19, #2-4)