Applied Surface Science (v.253, #13)
Sixth International Symposium by Władysław Rudziński; Małgorzata Witko (5565-5569).
Confinement effects on chemical reactions—Toward an integrated rational catalyst design by Erik E. Santiso; Milen K. Kostov; Aaron M. George; Marco Buongiorno Nardelli; Keith E. Gubbins (5570-5579).
Most chemical reactions of practical interest are carried out in nano-structured materials, which can enhance reactions due to their large specific surface area, their interactions with the reacting mixture and confinement effects. An experimental investigation of the role of each possible catalytic effect is challenging, since experimental measurements reflect an integration over multiple effects. In this work, we present a review of our most recent research on some of the factors that can influence a chemical reaction in confinement through the study of several model systems. We first consider the influence of steric hindrance on the equilibrium and kinetics for the rotational isomerizations of several small hydrocarbons [E.E. Santiso, M. Buongiorno Nardelli, K.E. Gubbins, Proc. Natl. Acad. Sci. U.S.A., (2007), in press]. These examples illustrate how reaction rates can vary doubly exponentially with the dimensions of the confining material (the ‘shape-catalytic’ effect). As a second example, we consider the unimolecular decomposition of formaldehyde on graphitic carbon pores of various sizes [E.E. Santiso, A.M. George, K.E. Gubbins, M. Buongiorno Nardelli, J. Chem. Phys. 125 (2006) 084711]. These results illustrate the influence of electrostatic interactions with the supporting material on the reaction mechanism and equilibrium yield for reactions involving a charge transfer. As a final example, we consider the interaction of a water molecule with a defective carbon substrate as an example of a chemical interaction that can be enhanced through a shape-catalytic effect. We first show using ab initio calculations how a vacancy site on a graphene surface can induce the thermal splitting of water at relatively low temperatures [M.K. Kostov, E.E. Santiso, A.M. George, K.E. Gubbins, M. Buongiorno Nardelli, Phys. Rev. Lett. 95 (2005) 136105]. We then examine the dissociation on a vacancy site on a nanotube surface, which shows the shape-catalytic effect of the surface curvature. These results are a first step toward the design of catalytic materials that take advantage of different enhancing effects simultaneously.
Keywords: Confinement effects; Catalyst design; Chemical reactions; Graphitic carbons;
Heat of adsorption and density distribution in slit pores with defective walls: GCMC simulation studies and comparison with experimental data by D.D. Do; D. Nicholson; H.D. Do (5580-5586).
The adsorption behavior (capacity, density distribution and packing density) and the isosteric heat versus loading in a slit pore whose walls contain defective graphene layers are investigated in this paper. The defective wall is characterized by the extent and size of the defect. Simulation results obtained with the Grand Canonical Monte Carlo method reveal complex patterns of isosteric heat, and this complex behavior is a result of the interplay between three factors: (i) the surface heterogeneity (solid–fluid interaction, sites with varying degree of affinity), (ii) fluid–fluid interaction and (iii) the overlapping of potentials exerted by the two defective walls. We illustrate this with argon adsorption in pores of various sizes, and results obtained from the simulation agree qualitatively with the experimental data at 77 K on Saran microporous S600H and micro-mesoporous S84 charcoals of Beebe et al. [R.A. Beebe, B. Millard, J. Cynarski, J. Am. Chem. Soc. 75 (1953) 839]. The S600H was found to contain pores predominantly in the neighborhood of 7 Å with 30% of defect and a defective size of 2.84 Å. This is consistent with the argument made by Beebe et al. that this sample is a microporous solid and most pores can accommodate only one layer. The other sample, S84, has larger pores than S600H, and it is found that it has a wider pore size distribution and the pore width is centered at about 12 Å.
Keywords: Grand Canonical Monte Carlo; Heat of adsorption; Density distribution; Simulation studies;
Applicability of classical methods of pore size analysis for MCM-41 and SBA-15 silicas by J. Choma; M. Jaroniec (5587-5590).
Two most popular ordered mesoporous silicas, MCM-41 and SBA-15, exhibiting uniform mesopores of approximately cylindrical shapes, have been used as model adsorbents for verification, improvement and/or development of adsorption-based methods for characterization nanoporous materials. While the applicability of the classical methods for pore size analysis was widely examined by employing MCM-41 materials, the large-pore materials such as SBA-15 did not find adequate usage for this type of studies. The current work addresses the issue of applicability of classical methods such as Barrett–Joyner–Hallenda (BJH) and Broekhoff–de Boer (BdB) methods for pore size analysis of mesoporous silicas by using MCM-41 and SBA-15 materials as model adsorbents. In addition, the Kruk–Jaroniec–Sayari (KJS) method, which is based on the BJH algorithm and experimental relations for the pore width and statistical film thickness, is discussed too. While the MCM-41 materials cover the range of small mesopores (about 2–7 nm), the inclusion of SBA-15 materials allowed us to examine the range of the pore diameters up to about 12 nm. The high quality MCM-41 and SBA-15 samples are used to discuss the applicability and limitations of the aforementioned characterization methods and to propose some recommendations for pore size analysis of these materials.
Keywords: MCM-41; SBA-15; Nitrogen adsorption; Ordered mesoporous silica; Pore size analysis;
Modeling of adsorption and phase diagrams for stepped surfaces: Transfer matrix approach by Alexander V. Myshlyavtsev; Marta D. Myshlyavtseva (5591-5595).
The simplest model of stepped surface has been constructed and scrutinized with different values of model parameters. The transfer matrix method was shown to be a very effective approach. Phase diagrams and local isotherms have been obtained. It was shown that the local coverage can be the non-monotonous function of the total coverage or the chemical potential.
Keywords: Modeling; Transfer matrix; Stepped surface; Phase diagrams; Isotherms;
Adsorption in cylindrical pores: Mixed lattice-site/off-site Monte Carlo simulations in pores with heterogeneous wall structure by B. Kuchta; L. Firlej; P. Boulet; M. Marzec (5596-5600).
We present results of grand canonical Monte Carlo simulations of adsorption in cylindrical pores with rough surface modeled by lattice-site approach. Each site is characterized by two parameters: structural and energetic, which locally modify the structure and energy properties of the surface. There are three types of sites, randomly distributed over the wall: attractive, neutral and repulsive with respect to the smooth pore model. The results presented here show how this model affects the mechanism of adsorption and how it changes the forms of adsorption isotherm. We compare our numerical results with the experimental data of adsorption of a simple fluid (CH4, T = 77 K) in cylindrical silica pore of diameter d = 4 nm (MCM-41 material).
Keywords: Nano-pores; Adsorption isotherm; Neutron diffraction; Computer simulations;
Melting mechanism of monolayers adsorbed in cylindrical pores: An influence of the pore wall roughness by B. Kuchta; L. Firlej; R. Denoyel; P. Boulet; S. Rols; M.R. Johnson (5601-5605).
We have analyzed the mechanism of melting of layers adsorbed in cylindrical pores of porous materials. The goal was to understand the melting mechanism of simple fluids adsorbed in pores with heterogeneous wall surface. The studied system was a monolayer of methane molecules adsorbed in MCM-41 pore of diameter d = 4 nm. Both experimental (neutron scattering) and simulation (Monte Carlo) results proved extremely strong influence of the wall roughness on the melting mechanism. The most striking difference between melting on smooth and rough surfaces was in the temperatures of the transition. The transformation between solid-like and liquid-like monolayer phases adsorbed on a rough surface was observed in a very large temperature range and the solid like properties were observed even above the bulk methane melting temperature.
Keywords: Nano-pores; Adsorption; Melting; Neutron diffraction; Monte Carlo;
Atomistic simulation of sorption in model pores with reduced spatial periodicity by Evangelia Pantatosaki; Aggelos Papaioannou; Athanassios K. Stubos; George K. Papadopoulos (5606-5609).
Grand Canonical Monte Carlo (GCMC) was used to study the sorption thermodynamics of carbon dioxide in model graphite slit-like pores and nanotubes by means of the Ewald technique, suitably adapted for the computation of long range (electrostatic) interactions of sorbates confined in pore systems exhibiting reduced periodicity in space. The computed thereby micropore size distributions extracted via mathematical elaboration of the simulation results with respect to real graphitic materials, reproduced successfully the experimentally measured isotherms of carbon dioxide in these materials at various temperatures. In the case of nanotubes, a direct Coulomb summation over a large number of periodic images proved to be a sufficient approximation leading to excellent agreement between the simulated and measured isotherms.
Keywords: Adsorption; Grand canonical Monte Carlo; Ewald technique; Graphite nanopores; Carbon dioxide;
Modeling of heterogeneous surfaces and characterization of porous materials by extending density functional theory for the case of amorphous solids by E.A. Ustinov; D.D. Do; V.B. Fenelonov (5610-5615).
A method of characterization of carbonaceous materials using nongraphitized carbon black as a reference is considered. The Tarazona density functional theory was applied to amorphous solids to describe nitrogen adsorption on nongraphitized carbon black. This allows us to describe energetic heterogeneity without the need to invoke any energy distribution functions. To derive the pore size distribution (PSD) of porous carbon whose pore walls are non-graphitized, we used the entropy concept in the regularization method. With this approach PSD is more well-behaved than that obtained with the usual means. We applied this new theory to study the effects of technological parameters on porous structure of a series of activated carbon.
Keywords: Density functional theory; Amorphous surface; Activated carbons; Characterization;
Complementary study of microporous adsorbents with DFT and LBET by Jan T. Duda; Linda Jagiełło; Jacek Jagiełło; Janina Milewska-Duda (5616-5621).
Results of pore structure analysis based on two essentially different interpretations of adsorption mechanisms and resultant mathematical models are discussed. The first model, exploiting the density functional theory (DFT), allows evaluating pore volume distribution with a presumed pore shape. The second, referred to as the LBET model, provides information on distribution of adsorbate clusters in micropores, which may be used to deduce the pore structure. To improve reliability of the structure evaluations, both models were fitted simultaneously to a set of adsorption isotherms of different probing adsorbates. Results of the analysis obtained, for two microporous carbons, by fitting their adsorption isotherms of Ar, N2, and H2 are discussed. Both DFT and LBET models gave relatively good fit to the experimental isotherms. The pore size distribution evaluated with the DFT model is qualitatively consistent with a picture of pore structure provided by the LBET description. The LBET approach yields less explicit information on the properties of pores, but it provides more detailed information about particular shapes of the isotherms.
Keywords: DFT; Pore size distribution; Adsorption energy distribution; Microporous materials;
Computer modeling of dissociative gas adsorption on laser-roughened surfaces by Paweł Szabelski; Tomasz Pańczyk (5622-5627).
A simple computer model of dissociative adsorption of diatomic molecules on a solid surface with laser-induced defects was proposed. The defects (ablation craters) were assumed to have either cubicoid or pyramidal shape, depending on the approximation level. Special attention was paid to the influence of a degree of structural disorder on the adsorptive properties of the surface. In particular, both equilibrium adsorption isotherms and temperature programmed desorption (TPD) spectra of non-interacting diatomic molecules from the surfaces subjected to a different number of laser pulses were simulated. The observed changes in the adsorptive properties of the surface were explained using simple geometric arguments linking the adsorption probability for a single molecule with the topography of the surface. For example, it was demonstrated that, for a sufficiently large number of laser pulses (N), the adsorption probability scales with 1 / N , regardless of the assumed crater shape. The obtained results also indicate that, in general, the surface roughness greatly affects the TPD spectra while it has minor influence on the shape of the adsorption isotherms.
Keywords: Laser ablation; Surface defects; Monte Carlo simulation; Dissociative adsorption; Thermal desorption;
Simulation study of argon adsorption on (0 0 1) faces of phyllosilicates by A. Palace Carvalho; J.P. Prates Ramalho; F. Villiéras (5628-5632).
Grand Canonical Monte Carlo molecular simulations have been performed for argon and nitrogen adsorption on the basal surfaces of phyllosilicates without surface cations. The results have been compared with derivative isotherms analysis of experimental data. An optimization of the surface–Ar interaction has been performed by varying the oxygen atom LJ ɛ/k B parameter and the optimized value was used to perform the nitrogen adsorption simulations. The analysis of the argon adsorption simulation indicates that adsorption mechanisms are more complex than may be suggested by experimental results obtained by low-pressure adsorption. The structure of the adsorbed film has a marked dynamic behaviour and the monolayer capacity strongly depends on the equilibrium relative pressure. For nitrogen adsorption, while high pressure behaviour is simulated adequately, some deviation is observed in low-pressure region of the isotherms suggesting that additional simulation and perhaps the use of a more sophisticated potential to model the nitrogen molecule can be necessary to understand fully the behavior of this gas on clay minerals.
Keywords: Phyllosilicates; Talc; Derivative adsorption isotherms; GCMC;
Study of structural irregularities of smectite clay systems by small-angle neutron scattering and adsorption by A. De Stefanis; A.A.G. Tomlinson; Th.A. Steriotis; G.Ch. Charalambopoulou; U. Keiderling (5633-5639).
Small angle neutron scattering (SANS) and its contrast-matching variant are employed in order to determine structural properties (inter-pillar distances and mass/surface fractal dimensions of the clay layers and pillars) of a series of smectite natural clays (montmorillonite, beidellite, and bentonite) and their pillared and pillared/ion-exchanged analogues. Moreover, a comparative analysis with the adsorption data is carried out on the basis of a systematic study of the structural changes induced by a particular treatment or modification (e.g. pillaring) of the clay systems.
Keywords: Pillared clays; Adsorption; Small angle neutron scattering; Fractal dimension;
Comparative analysis of heterogeneous solid and soft materials by adsorption, NMR and thermally stimulated depolarisation current methods by V.M. Gun’ko; V.V. Turov; R. Leboda; V.I. Zarko; J. Skubiszewska-Zięba; B. Charmas (5640-5644).
Structural characterisation of such bio-objects as fibrinogen solution, yeast cells, wheat seeds and bone tissues has been done using two versions of cryoporometry based on the integral Gibbs–Thomson (IGT) equation for freezing point depression of pore liquids and the measurements by 1H NMR spectroscopy (180–200 < T < 273 K) and the thermally stimulated depolarisation current (TSDC) method (90 < T < 273 K) of structured water. The IGT equation was solved using a self-consisting regularization procedure including the maximum entropy principle applied to the distribution function of pore size (PSD). Both methods give clear pictures of changes in the structural characteristics caused, e.g., by hydration and swelling of wheat seeds and yeast cells, coagulation and interaction of fibrinogen with solid nanoparticles in the aqueous media, and the human bone tissue disease.
Keywords: Fibrinogen; Yeast cells; Bone tissue; Structural characteristics; Pore water; 1H NMR; TSDC; Cryoporometry;
Excess surface work—A modelless way of getting surface energies and specific surface areas directly from sorption isotherms by Jürgen Adolphs (5645-5649).
Sorption isotherms can be easily transformed into excess surface work (ESW) isotherms, computed as the product of the adsorbed amount and the change in chemical potential. Plotted against the amount adsorbed at least one minimum is yield. Thermodynamically ESW is the sum of the surface free energy and the isobaric isothermal work of sorption. Therefore, ESW is not a model, instead it is just another way of presenting an isotherm. From the amount adsorbed in the first minimum one can obtain a specific surface area similar to the BET surface area. The depth of the ESW in the minimum gives a sorption energy, which corresponds approximately to the loss of degrees of freedom of the sorptive. In this contribution the ESW plots of various sorption isotherms on highly ordered alumina with cylindrical pores of 25 nm width and mesoporous SBA 15 will be presented and discussed.
Keywords: Sorption; Excess surface work; Sorption energy; Sorption model;
Studies on ordered mesoporous materials for potential environmental and clean energy applications by Yan Sun; Xiu-Wu Liu; Wei Su; Yaping Zhou; Li Zhou (5650-5655).
Two series of ordered mesoporous materials, SBA-15 silica and CMK-3 carbon were synthesized. The ordered nanostructure of these materials was confirmed by TEM and XRD analysis. Structural parameters including the specific surface area, pore volume and pore size distribution were determined on the basis of nitrogen adsorption data at 77 K. Potential applications of these materials were explored in relation to the CO2 sequestering, methane storage and fuel desulfurization. Initial studies of both materials showed their usefulness for environmental and clean energy applications. SBA-15 modified with triethanolamine showed a very good adsorption selectivity for CO2 while its adsorption reversibility was retained. Also, this material after CuCl deposition was useful for removal of fuel thiophenes. However, CMK-3 was shown to be promising material for storage of natural gas. As high as 41 wt.% of methane was stored in this material in the presence of appropriate amount of water.
Keywords: Mesoporous materials; Ordered mesostructures; SBA-15; CMK-3; Environmental applications; Clean energy applications;
Template-directed synthesis of highly ordered nanoporous graphitic carbon nitride through polymerization of cyanamide by Sohee Hwang; Seungho Lee; Jong-Sung Yu (5656-5659).
The fabrication of well-ordered nanoporous graphitic carbon nitride by condensation of cyanamide (CN–NH2) as a molecular precursor using a colloidal silica crystalline array as a template is described. The resulting sample exhibited a three-dimensionally extended highly ordered pore array as shown by transmission electron microscopy, scanning electron microscopy and nitrogen isotherms. The carbon nitride structure revealed high graphitic nature with C3N4 stoichiometry. In particular, the C3N4 network structure consists of tri-s-triazine rings (C6N7) cross-linked by trigonal N atoms.
Keywords: Carbon nitride; Graphitic nature; Highly ordered nanopores; Nanoporous carbon;
Adsorption studies of thermal stability of SBA-16 mesoporous silicas by R.M. Grudzien; B.E. Grabicka; M. Jaroniec (5660-5665).
Cage-like ordered mesoporous silicas, SBA-16, and ethane-silicas with cubic (Im3m) and (Fm3m) symmetry groups were synthesized with addition of sodium chloride by using tetraethyl orthosilicate (TEOS) as silica precursor, 1,2-bis(triethoxysilyl)ethane (BTESE) as bridged silsesquioxane and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) triblock copolymer Pluronic F127 (EO106PO70EO106) as template at low acid concentrations. The resulting samples were subjected to extraction in order to remove the polymeric template. The as-synthesized and extracted materials were calcined in the range of 350–900 °C to determine their thermal stability. Based on the XRD analysis and nitrogen adsorption data such as the BET specific surface area, volume of primary mesopores, pore wall thickness and pore size distributions, the SBA-16 silicas exhibit relatively high thermal stability because their mesostructural ordering was retained even up to 900 °C. However, an increase in the calcination temperature tended to decrease significantly the BET surface area, volumes of primary and complementary pores, and to less extent the pore size and pore wall thickness due to the structural shrinkage. Furthermore, the as synthesized samples subjected to a short extraction with acidic ethanol solution possessed even better thermal stability. On the other hand, calcination at 550 °C of ethane-silicas caused a complete removal of the ethane bridging groups from the periodic mesoporous organosilicas and their calcination above 800 °C led to the partial collapse of the structure.
Keywords: Adsorption; Cage-like mesoporous materials; Mesoporous ethane-silica; SBA-16; Thermal stability;
Characterization and adsorptive application of ordered mesoporous silicas by Rico Rockmann; Grit Kalies (5666-5670).
The adsorption behaviour of the n-octane/ethanol binary liquid mixture has been studied on ordered mesoporous silica materials. Adsorption excesses on SBA-15, SBA-16 and MCM-48 solids are measured and described by mathematical functions. The experimental adsorption excess isotherms are presented and discussed. The mesoporous silicas used for liquid-adsorption experiments are characterized by nitrogen adsorption before and after liquid adsorption by the powder X-ray diffraction (XRD) and by the sample controlled thermal analysis (SCTA).
Keywords: Adsorption excess; Binary liquid mixture; Liquid/solid interface; Ordered mesoporous solid; Characterization; Thermal analysis;
Theoretical studies of argon adsorption in MCM-41 mesoporous systems by Yu.K. Tovbin; A.G. Petukhov (5671-5675).
Adsorption isotherms are predicted for spherical adsorbates in cylindrical channels of MCM-41 mesoporous materials over a wide range of temperatures by using the “fragment method”. This prediction shows that an equilibrium capillary condensation is impossible for pores with diameters smaller than 2.5 nm. The adsorbate distribution in relatively large pore channels was described by the quasi-chemical approximation (QCA) that takes into account direct pair correlations between interacting molecules. In order to improve the lattice–gas model in the vicinity of the critical point, a calibration function that takes into account information from the fragment method, was introduced into the QCA equations. The influence of the size factor of pores on argon adsorption isotherms was demonstrated.
Keywords: Molecular theory; Lattice–gas model; Narrow pores; Phase transition; Quasi-chemical approximation; Argon–silica system; MCM-41;
Assessment of pore structure parameters for polymer-templated mesoporous molecular sieves by means of nitrogen and argon adsorption by I. Nowak; M. Jaroniec (5676-5681).
Pore size, wall thickness, and microporosity of polymer-templated mesoporous silica (PTMS) can be controlled by using different nonionic triblock copolymers as soft templates. The evolution of the pore structure of PTMS was studied by using nitrogen and argon adsorption at 77 K in addition to powder X-ray diffraction and transmission electron microscopy.
Keywords: SBA-15; Nitrogen adsorption; Argon adsorption; Structural characterization; Mesoporous silica; Block copolymers;
Comparative studies of p6m siliceous mesostructures by powder X-ray diffraction and nitrogen adsorption by S. Pikus; L.A. Solovyov; M. Kozak; M. Jaroniec (5682-5687).
Two-dimensional mesostructures with p6m symmetry such as MCM-41 and SBA-15 are the subject of intensive studies by using nitrogen and argon adsorption, transmission electron microscopy, and powder X-ray diffraction/scattering techniques. The latter may involve the X-ray diffraction (XRD) or small angle X-ray scattering (SAXS) measurements. The XRD/SAXS patterns for the aforementioned ordered mesostructures often exhibit four or more reflections, the most intensive one, 1 0 0 peak, and three less intensive peaks, 1 1 0, 2 0 0, 2 1 0. So far, analysis of these patterns was usually limited for the evaluation of the unit cell parameter and the identification of the observed peaks. In this work we present an attempt to analyze the XRD/SAXS patterns by including not only the position of observed peaks but also their intensity. It is shown that the intensity of these peaks, especially 1 1 0 peak, depends on the ratio of the pore diameter to the unit cell parameter. In particular, this dependence was studied for the intensity ratio of 1 1 0 and 2 0 0 peaks assuming 2 0 0 peak as a reference reflection because of its nearness to 1 1 0 peak (which minimizes the influence of other factors than the structural ones on the 1 1 0/2 0 0 intensity ratio analysis) and similar intensity to that of 1 1 0 peak. The values of the 1 1 0/2 0 0 intensity ratio were determined for many MCM-41 and SBA-15 samples and analyzed in relation to the pore width/unit cell ratio, where the pore width was estimated on the basis of nitrogen adsorption data or by the XRD/SAXS structure modeling. Comparative analysis of this intensity ratio for numerous MCM-41 and SBA-15 samples allows for a quick estimation of the pore width and provides some information about hexagonality of mesopores in these materials.
Keywords: Adsorption; Powder XRD; MCM-41; SBA-15; Structure characterization; SAXS;
Evidence of surface active sites on NaY zeolite by a model reaction by V. Santos; K. Barthelet; A.A. Quoineaud; T. Armaroli; I. Gener; P. Magnoux (5688-5691).
Owing to the development of a new test reaction, namely the isomerization of 1-dodecene, it becomes possible to characterize the activity of cationic zeolites under conditions close to those of industrial adsorption and separation processes (temperature around 150–200 °C and liquid phase). Indeed, 1-dodecene is highly active and still in a liquid state at 150 °C. Furthermore, by comparing the reactivity of NaY before and after treatments applied to reduce its activity ((i) passivation of the external surface by deposition of TetraEthylOrthoSiloxane (TEOS) and (ii) washing the zeolite with a basic or neutral solution), we are able to propose a nature and localization for the residual active sites of this zeolite. Indeed, the evolution of the NaY activity in their function indicates that the active sites are located both at the external and internal surfaces of NaY and that two types of sites can be described: OH groups and structure defects.
Keywords: Acidity; NaY; Surface modifications; Test reaction; 1-Dodecene isomerization;
Influence of isomorphous substitution in MFI-type materials on the diffusion of n-hexane: Molecular dynamic studies by J. Wloch (5692-5695).
Theoretical studies of the behaviour of an adsorption system MFI/n-hexane were performed with a molecular dynamic method. Investigation of influence of isomorphous substitution on diffusion coefficients was the main objective. It was found that the presence of metals other than silicon in the zeolite framework might cause an increase in the diffusion coefficients. However, it is small, independently of the adsorption level.
Keywords: Zeolites; Isomorphic substitution; Diffusion; MD simulation;
A new theoretical approach to the encapsulation of small molecules in zeolites by Mee Kyung Song; Jung Sup Kim; Kyoung Tai No (5696-5700).
We present a new theoretical method to study the encapsulation of small molecules such as H2, O2, N2, Ar and CH4 in the Cs3Na9-A zeolite. To study the properties of encapsulated molecules, we used the Fermi–Dirac like statistics. The density of states, the distribution function, average binding energy and the average activation energy of encapsulated molecules are calculated. As the number of encapsulated molecules in zeolite cavities increases, the higher energy states in the cavities are gradually filled and, consequently, the activation energy for decapsulation is lowered. We also calculated the fraction of molecules with higher energy than their activation energy, revealing that the activation energy for decapsulation depends not only on the temperature but also on the number of the encapsulated molecules.
Keywords: Encapsulation; Cs3Na9-A zeolite; Potential energy surface; Fermi–Dirac like statistics; Activation energy;
Variable temperature FT-IR studies on hydrogen adsorption on the zeolite (Mg,Na)-Y by C. Otero Areán; G. Turnes Palomino; M.R. Llop Carayol (5701-5704).
Variable-temperature infrared spectroscopy was used for the thermodynamic studies on the adsorption of hydrogen on the zeolite (Mg,Na)-Y. Adsorption renders the H―H stretching mode infrared active, and simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, over a range of temperature, allowed adsorption enthalpy and entropy to be determined. The standard adsorption enthalpy and entropy resulted to be ΔH° = −18.2(±0.8) kJ mol−1 and ΔS° = −136(±10) J mol−1 K−1, respectively. The adsorption enthalpy is substantially higher than the hydrogen liquefaction heat, which suggests that magnesium-containing porous materials are potential candidates in the search for suitable adsorbents for reversible hydrogen storage.
Keywords: Adsorption enthalpy; Hydrogen adsorption; Hydrogen storage; Infrared spectroscopy; Zeolites;
Thermodynamics of nitrogen adsorption on the zeolite H-FER by M. Rodríguez Delgado; C. Otero Areán (5705-5708).
Adsorption (at a low temperature) of nitrogen on the protonic zeolite H-FER results in hydrogen bonding of the adsorbed N2 molecules with the zeolite Si(OH)Al Brønsted acid groups. This hydrogen bonding interaction leads to activation, in the IR, of the fundamental N―N stretching mode, which appears at 2331 cm−1. From the infrared spectra taken over a temperature range, while simultaneously recording integrated IR absorbance, temperature and nitrogen equilibrium pressure, the thermodynamics of the adsorption process was studied. The standard adsorption enthalpy and entropy resulted to be ΔH° = −20(±1) kJ mol−1 and ΔS° = −131(±10) J mol−1 K−1, respectively.
Keywords: Adsorption thermodynamics; Ferrierite; Infrared spectroscopy; Nitrogen adsorption; Zeolites;
Investigation of surface properties of lunar regolith: Part I by E. Robens; A. Bischoff; A. Schreiber; A. Dąbrowski; K.K. Unger (5709-5714).
This paper describes an initial investigation of the surface properties of three lunar soil samples from the Apollo 11, 12 and 16 missions, respectively. We report on density measurements using a helium pycnometer, adsorption isotherms of krypton applied for the determination of specific surface area of the samples and gravimetric measurement of the isotherms of water, heptane and octane. Electron-microscopic photographs are described and discussed.
Keywords: Moon; Regolith; Surface; Adsorption; Water;
Characterization of nanoporous carbons by combining CO2 and H2 sorption data with the Monte Carlo simulations by M. Konstantakou; Th.A. Steriotis; G.K. Papadopoulos; M. Kainourgiakis; E.S. Kikkinides; A.K. Stubos (5715-5720).
The Monte Carlo method in its grand ensemble variant (GCMC) is used in combination with experimental data in order to characterize microporous carbons and obtain the optimal pore size distribution (PSD). In particular, the method is applied in the case of AX-21 carbon. Adsorption isotherms of CO2 (253 and 298 K) and H2 (77 K) up to 20 bar have been measured, while the computed isotherms resulted from the GCMC simulations for several pore widths up to 3.0 nm. For the case of H2 at 77 K quantum corrections were introduced with the application of the Feynman–Hibbs (FH) effective potential. The adsorption isotherms were used either individually or in a combined manner in order to deduce PSDs and their reliability was examined by the ability to predict the experimental adsorption isotherms. The combined approach was found to be capable of reproducing more accurately all the available experimental isotherms.
Keywords: Activated carbons; Pore size distribution; GCMC simulations;
Effects of textural and surface characteristics of microporous activated carbons on the methane adsorption capacity at high pressures by M. Bastos-Neto; D.V. Canabrava; A.E.B. Torres; E. Rodriguez-Castellón; A. Jiménez-López; D.C.S. Azevedo; C.L. Cavalcante (5721-5725).
The objective of this study is to relate textural and surface characteristics of selected microporous activated carbons to their methane storage capacity. In this work, a magnetic suspension balance (Rubotherm, Germany) was used to measure methane adsorption isotherms of several activated carbon samples. Textural characteristics were assessed by nitrogen adsorption on a regular surface area analyzer (Autosorb-MP, by Quantachrome, USA). N2 adsorption was analysed by conventional models (BET, DR, HK) and by Monte Carlo molecular simulations. Elemental and surface analyses were performed by X-ray photoelectronic spectroscopy (XPS) for the selected samples. A comparative analysis was then carried out with the purpose of defining some correlation among the variables under study. For the system under study, pore size distribution and micropore volume seem to be a determining factor as long as the solid surface is perfectly hydrophobic. It was concluded that the textural parameters per se do not unequivocally determine natural gas storage capacities. Surface chemistry and methane adsorption equilibria must be taken into account in the decision-making process of choosing an adsorbent for gas storage.
Keywords: Surface chemistry; Methane adsorption; Adsorbent;
CO2 sorption on substituted carbon materials by P.A. Gauden; M. Wiśniewski (5726-5731).
Theoretical study of sorption of CO2 on the 4-ring graphene (“unmodified” or N-, O-, and OH-substituted) structures possessing one completely unsaturated edge zigzag site is reported using the DFT (B3LYP/6-31G(d,p)) method. Lactone and heterocyclic complexes (due to thermodynamic favourability) are taken into account. The analysis of theoretical results shows that the enthalpy of reaction strongly depends on the chemical nature, i.e. the position of the doping of atom(s) is crucial. All substitutions do not change or decrease the enthalpy in comparison with the “unmodified” graphene sheet. The well-known theoretical reactivity indices (ionization potential, electron affinity, global softness, and HOMO–LUMO gaps) are calculated for the studied adsorbents in order to explain the above-mentioned tendencies. Finally, the effect of the presence of heteroatoms on the enthalpy of reaction (ΔH 298) for all CO2–heteroatom–doping adsorbent complexes is shown. Thus, carbon dioxide molecules adsorb on the edge plane surface of N-, O-, OH-containing carbon surfaces similarly or much less favourably in comparison with the “unmodified” adsorbents. This confirms some experimental observations.
Keywords: Activated carbon; Chemisorption; Computational chemistry; Thermodynamic analysis; Reactivity; Gaussian 98; DFT;
Sorption of methane and carbon dioxide mixtures in Polish hard coals considered in terms of adsorption-absorption model by G.S. Jodłowski; P. Baran; M. Wójcik; A. Nodzeński; St. Porada; J. Milewska-Duda (5732-5735).
The measurements of gas mixture sorption of CO2 + CH4 (50%:50%) on hard coals were carried out using an original measurement method. The accuracy of the experimental data was controlled by using a gas chromatograph. Experimental sorption isotherms of individual gases were used for the simulation of sorption of their mixtures. A good agreement was obtained between the simulated and experimental data.
Keywords: Gas mixture sorption; Hard coals; Multisorption model; Thermodynamical analysis;
Phosphoric acid activation—Functionalization and porosity modification by A.M. Puziy; O.I. Poddubnaya; B. Gawdzik; M. Sobiesiak; M.M. Tsyba (5736-5740).
4,4′-Bis(maleimidodiphenyl) methane (BM) and divinylbenzene (DVB) copolymers with different compositions were used for production of carbons by carbonization and phosphoric acid activation. It has been shown that both BM and DVB polymers are good carbon precursors which show the same potential to produce carbonaceous material. However, despite cross-linked nature of all polymers, BM softens before formation of coke giving non-porous material. Phosphoric acid activation of polymer precursor increased the yield, surface area and pore volume as compared to acid-free heat treatment. Phosphoric acid activation of polymer precursor resulted in carbon material containing 6–8% of phosphorus and considerable amount of surface acidic groups of four types (total 2.6–3.2 mmol/g) which are responsible for metal ion adsorption from aqueous solutions.
Keywords: Polymer carbon; Carbonization; Chemical activation; Pore-size distribution; Acid–base properties; pK distribution;
Effects of activated carbon properties on the adsorption of naphthalene from aqueous solutions by C.O. Ania; B. Cabal; C. Pevida; A. Arenillas; J.B. Parra; F. Rubiera; J.J. Pis (5741-5746).
The aim of this work was to investigate the role of porous and chemical heterogeneities of activated carbons in the adsorption of naphthalene from aqueous media. A commercially available activated carbon was used as the adsorbent, and its surface heterogeneity was systematically altered by heat treatment at 450 and 850 °C, obtaining a series of carbons with various oxygen contents and similar surface functionalities. The results confirmed that the adsorption of naphthalene depends strongly on the pore size distribution of the adsorbent, particularly narrow microporosity. Moreover, oxygen functionalities reduced the accessibility and affinity of naphthalene to the inner pore structure via formation of hydration clusters. Consequently, the hydrophobic/hydrophilic character of the adsorbent is important, since it dominates the competitive adsorption of water. Adsorbents with a high non-polar character (i.e., low oxygen content) have proven to be more efficient for naphthalene adsorption.
Keywords: PAH; Adsorption; Liquid phase; Activated carbon;
Ethylene and phenylene bridged polysilsesquioxanes functionalized by amine and thiol groups as adsorbents of volatile organic compounds by A. Dąbrowski; M. Barczak; E. Robens; N.V. Stolyarchuk; G.R. Yurchenko; O.K. Matkovskii; Yu.L. Zub (5747-5751).
Ethylene and phenylene bridged polysilsesquioxane xerogels having amine and thiol groups attached to the surface have been obtained by the sol–gel method from 1,2-bis(triethoxysilyl)ethane or 1,4-bis(triethoxysilyl)benzene and functionalized silanes in the presence of an ammonium fluoride catalyst in an ethanol solution. The synthesized samples have a porous structure (700–850 m2/g) and a high content of functional groups (1.4–1.9 mmol/g). The obtained porous bridged polysilsesquioxanes exhibit a considerable affinity for adsorbing several organic compounds (n-hexane, n-heptane, benzene, cyclohexane, acetonitrile and triethylamine) from the gas phase. The sample with an ethylene bridge and amino groups in the surface layer has the highest uptake of all compounds. Data from adsorption measurements show that functionalized organosilicon materials can be used as effective adsorbents of organic contaminants from the gas phase.
Keywords: Sol–gel method; Bridged polysilsesquioxanes; Xerogels; Porosity; Hybrid materials; Adsorption;
The impact of carbon surface chemical composition on the adsorption of phenol determined at the real oxic and anoxic conditions by Artur P. Terzyk (5752-5755).
The results of phenol adsorption–desorption isotherms (at 310 K) measured on the series of activated carbons (D43/1, NORIT RO 0.8, D55/2) are presented. The effect of carbon surface chemical composition on phenol adsorption determined at real oxic and anoxic conditions is discussed. To obtain the real anoxic conditions the two station controlled atmosphere chamber with two catalyst heater units (Plas Labs, Lansing, MI, USA) was applied. It is shown that the adsorption under oxic conditions is always larger than that determined for anoxic ones for all studied carbons. The analysis of those differences shows that in the range of micropore filling they decrease with the equilibrium phenol mole fraction in solution. Contrary they increase after micropores being filled. The average differences between the adsorption properties are the linear function of the concentration of surface acidic groups (assigned from the Boehm's method as “carboxylic”) calculated per the apparent BET surface area of studied carbons.
Keywords: Adsorption from solution; Phenol adsorption; Activated carbon; Oxidative coupling;
Removal of aliphatic amino acids by hybrid organic–inorganic layered compounds by Fabiano Silverio; Márcio José dos Reis; Jairo Tronto; João Barros Valim (5756-5761).
Amino acids have been extensively used in several processes of the pharmaceutical and food industries. Treatments for the recovery and reuse of the wastewaters generated from these processes are few and little known. This work aims at studying the influence of variables like temperature, pH and ionic strength on the adsorption of the amino acids Asp and Glu, contained in aqueous solutions, on layered double hydroxides of the Mg–Al–CO3–LDH system. The adsorption experiments were performed at two different temperatures (298 and 310 K), two different pH values (7.0 and 10.0), and two ionic strength conditions (with or without the addition of NaCl). The adsorption isotherms exhibited similar profiles under the various conditions studied: an increase in temperature as well as an increase in the pH value decreased the amount of adsorbed amino acid while an increase in the ionic strength increased Asp and Glu adsorption. The PXRD analysis showed that the diffractograms obtained before and after the adsorption of amino acids have a similar pattern. The FT-IR spectra of the adsorbed material presented specific bands, which are related to the amino acids. The concentration range varied up to the anion solubility product and the extraction rate lay between 2.7 and 23.4% at higher equilibrium concentrations, showing that Mg–Al–CO3–LDH is efficient at removing the amino acids from the aqueous medium.
Keywords: Hydrotalcite; Layered double hydroxides; Aspartic acid; Glutamic acid; Adsorption;
Nitrate removal using natural clays modified by acid thermoactivation by C.J. Mena-Duran; M.R. Sun Kou; T. Lopez; J.A. Azamar-Barrios; D.H. Aguilar; M.I. Domínguez; J.A. Odriozola; P. Quintana (5762-5766).
Groundwater pollution by nitrates is a widespread problem in many locations in the world. The underground aquatic mantle of the Peninsula of Yucatan is highly vulnerable due to its karstic nature. Adsorption methods are a good choice for nitrate elimination. In this work, a natural calcium bentonite was modified by acid thermoactivation with HCl and H2SO4, and tested as a media for nitrate removal in an aqueous solution. The nitrate concentration in the solution was measured by FT-IR, using the Lambert–Beer law. Clay characterization was carried out by X-ray diffraction and FT-IR spectroscopy; surface area was measured by the BET method.
Keywords: Nitrates; Adsorption; Montmorillonites; Infrared spectroscopy; X-ray diffraction; BET;
Pore structures in an implantable sol–gel titania ceramic device used in controlled drug release applications: A modeling study by Aaron Peterson; Tessy Lopez; Emma Ortiz Islas; Richard D. Gonzalez (5767-5771).
Several process variables, which may be helpful in optimizing the rate at which drugs are released from implantable, sol–gel titania devices have been identified in this study. The controlled rate of drug release is compared for two different anticonvulsant drugs, valproic acid and sodic phenytoin. Contrary to what one might expect, when the concentration is increased in the titania reservoir the rate of initial drug delivery decreases. This is a desirable result, because it may reduce the danger of a high initial discharge, which may harm the epileptic rat. The structure of the porous structure within the titania network has been studied using a generalized form of the BET equation which considers only n layers. In general, following an initial discharge, the rate at which the drug is released will increase with the increasing concentration. Pore mouth blocking can present a problem. However, this problem tends to disappear following the initial discharge. The extent of drug loading is a useful variable parameter, which can be adjusted in order to deliver the amount of drug required in a given application.
Keywords: Epilepsy; Controlled drug release; Implantable devices; Pore structures; Titania;
Synthesis of an innovative calcium-alginate magnetic sorbent for removal of multiple contaminants by S.F. Lim; J. Paul Chen (5772-5775).
A new calcium-alginate magnetic sorbent has been prepared by an electrostatic extrusion technique. The sorbent has the calcium alginate as a bio-polymeric shell and iron oxides as magnetic cores. It is characterized by a multifunctional property: ease in separation via magnetic force, and effective adsorption of arsenic(V) and copper ions. It has been found that the equilibrium time of copper and arsenic(V) can be attained in less than 3 and 25 h, respectively. The maximum adsorption capacities of arsenic and copper ions are 6.75 and 60.24 mg/g, respectively, which are much higher than those of commercial adsorbents. Solution pH plays a key role in adsorption. The adsorption of arsenic increases as the pH is decreased. On the other hand, higher pH can enhance adsorption of copper ions.
Keywords: Calcium-alginate magnetic particles; Arsenic; Copper; Adsorption;
Modelling self-assembling of colloid particles in multilayered structures by Zbigniew Adamczyk; Paweł Weroński; Jakub Barbasz; Marta Kolasińska (5776-5780).
Simulations of particle multilayer build-up in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer having an arbitrary coverage of adsorption centers was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to 20) was simulated by assuming short-range interaction potentials for two kinds of particles of equal size. Interaction of two particles of different kind resulted in irreversible and localized adsorption upon their contact, whereas particles of the same kind were assumed to interact via the hard potential (no adsorption possible). Using this algorithm theoretical simulations were performed aimed at determining the particle volume fraction as a function of the distance from the interface, as well as the multilayer film roughness and thickness as a function of the number of layers. The simulations revealed that particle concentration distribution in the film was more uniform for low precursor layer density than for higher density, where well-defined layers of closely packed particles appeared. On the other hand, the roughness of the film was the lowest at the highest precursor layer density. It was also predicted theoretically that for low precursor layer density the film thickness increased with the number of layers in a non-linear way. However, for high precursor layer density, the film thickness increased linearly with the number of layers and the average layer thickness was equal to 1.58 of the particle radius, which is close to the closely packed hexagonal layer thickness equal to 1.73. It was concluded by analysing the existing data for colloid particles and polyelectrolytes that the theoretical results can be effectively exploited for interpretation of the LbL processes involving colloid particles and molecular species like polymers or proteins.
Keywords: Adsorption of colloid particles; Colloid adsorption; Deposition of particles; Hard sphere adsorption; Irreversible adsorption of colloid particles; Multilayer adsorption of particles; Polyelectrolyte adsorption; Random sequential adsorption; Simulations of multilayer adsorption; Self-assembling of colloid particles;
Self-assembled and fluorescence enhancement of semiconductor nanoparticles induced by surfactant adsorption by M. Quintana; E. Pérez (5781-5784).
When semiconductor colloidal CdS nanoparticles and nonylphenol are mixed together in dimethyl sulfoxide at room temperature, a self-assembling process is induced. In the course, the size tunable properties of CdS nanoparticles are amplified. A blue shift in the emission spectrum and a strong photoluminescence enhancement are observed without significant change in the absorption features of the colloidal nanoparticles. These results are attributed to the adsorption of nonylphenol onto the nanoparticles surface and to the association process of the surfactant molecules. The surfactant adsorption process provides a nanoparticle surface passivation and induces an associative phase that enlarges the photoluminescence stability. This strategy opens the possibility to improve simultaneously physicochemical and photoluminescence properties of nanocrystals in solution as well as to control their deposition on two-dimensional surfaces.
Keywords: Semiconductor nanoparticles; Photoluminescence enhancement; Blue shift; Surfactant adsorption;
Influence of surface heterogeneity in electroosmotic flows—Implications in chromatography, fluid mixing, and chemical reactions in microdevices by Alessandra Adrover; Massimiliano Giona; Francesca Pagnanelli; Luigi Toro (5785-5790).
We analyze the influence of surface heterogeneity, inducing a random ζ -potential at the walls in electroosmotic incompressible flows. Specifically, we focus on how surface heterogeneity modifies the physico-chemical processes (transport, chemical reaction, mixing) occurring in microchannel and microreactors. While the macroscopic short-time features associated with solute transport (e.g. chromatographic patterns) do not depend significantly on ζ -potential heterogeneity, spatial randomness in the surface ζ -potential modifies the spectral properties of the advection–diffusion operator, determining different long-term properties of transport/reaction phenomena compared to the homogeneous case. Examples of physical relevance (chromatography, infinitely fast reactions) are addressed.
Keywords: Microflows; Electroosmosis; Surface heterogeneity; ζ -Potential; Chromatography;
Modelling of ζ-potential of the montmorillonite/electrolyte solution interface by Piotr Zarzycki; Paweł Szabelski; Wojciech Piasecki (5791-5796).
The electrokinetic potential (ζ-potential) is calculated using the combination of the Poisson–Boltzmann equation and the Surface Complexation Models for energetically heterogeneous surface. This approach gives negative values of ζ for the whole pH region, which is in agreement with the published results of ζ-potential measurements. Moreover, the correct changes of ζ-potential values for different types of montmorillonite are observed. It is shown that electrokinetic properties of the considered systems are not as sensitive to surface heterogeneity as the adsorption isotherms and surface charge densities. As it was shown in our previous paper [P. Zarzycki, F. Thomas, J. Colloid Interface Sci. 302 (2006) 547–559], the presented model predicts parallel titration curves for reasonably small equilibrium constants of exchange processes. Here, we show further development of this model in order to predict ζ-potential.
Keywords: Surface heterogeneity; Zeta-potential; Montorillonite/electrolyte interface;
Mechanism of charging of the pyrite/aqueous interface as deduced from the surface potential measurements by Tajana Preočanin; Mihaela Tuksar; Nikola Kallay (5797-5801).
Surface potential of pyrite in an aqueous environment was measured by means of a single crystal pyrite electrode. The effect of the activity of S2− and Fe2+ ions as well as of pH, was examined. The results show that S2− and Fe2+ ions are the dominant potential determining ions. These ions are bound to surface sites with the extent depending on their activity in the bulk of the solution. Adsorption affinity of S2− ions is significantly higher than that of Fe2+ ions so that in most cases the pyrite surface is negatively charged. The results were explained on the basis of the surface complexation model. It was found that the surface potential depends also on pH.
Keywords: Pyrite; Surface charge; Surface potential; Adsorption;
Depletion potentials between colloids and patterned surfaces by Paweł Bryk; Stefan Sokołowski (5802-5806).
Effective interactions between the hard-sphere colloids and the patterned substrates created by depositing one or more hemispheres on the structureless walls are studied. The deposition of only one hemispherical cap gives rise to a new global minimum of the depletion potential but the difference from the planar hard wall case is moderate. On the other hand, when the hemispherical caps form a periodic array, multiple overlaps of the excluded volumes lead to formation of deep global minimum of the depletion potential. In some cases this minimum is deeper than − 10 k B T and this is more than triple of the potential minimum for the structureless wall. We conclude that templated surfaces affect depletion potentials significantly. This effect will have a major impact even when the residual attractive/repulsive interactions are present.
Keywords: Depletion forces; Density functional theory; Asakura–Oosawa approximation; Sterically stabilized colloids; Templated surfaces;
Flow microcalorimetry: Experimental development and application to adsorption of heavy metal cations on silica by Sébastien Lantenois; Bénédicte Prélot; Jean-Marc Douillard; Karol Szczodrowski; Marie-Christine Charbonnel (5807-5813).
Sorption of metal ions at the oxide mineral–water interfaces is a complex process involving many various contributions that can be explained using thermodynamics. The aim of this study is to obtain experimental thermodynamic data on adsorption of two heavy metal ions (Cd(II) and Pb(II)) on macroporous silica. Thermal signals of adsorption are studied by flow microcalorimetry which has been preferred because physico-chemicals conditions (pH, equilibrium concentration,…) can be controlled (the routine configuration was optimized in order to get a very stable pressure baseline and avoid important fluctuations in the determination of heat). Mechanisms driving the adsorption have been explained. The calculation of the effective charge of ions determined from the speciation diagrams and of the surface charges shows that the interactions between the two metals and the silica surface are mainly electrostatic. The differential enthalpies of adsorption Δads H have been experimentally measured. The heat of cadmium adsorption is low, endothermic and quantitatively equivalent to that of desorption. In the case of lead, the adsorption is athermal. Free energies and entropic effects related to cation adsorption have then been deduced according to the Gibbs’law. The entropy is positive during the adsorption process and at this temperature (298 K) is quite equivalent to free energy. This entropy is due to modification of hydration shell of the ions during their insertion into the interfacial region.
Keywords: Silica; Adsorption; Heavy metal; Flow microcalorimetry; Entropic effects;
Application of the statistical rate theory of interfacial transport to investigate the kinetics of divalent metal ion adsorption onto the energetically heterogeneous surfaces of oxides and activated carbons by W. Piasecki; W. Rudziński (5814-5817).
Divalent metal cation adsorption from solution onto oxides or activated carbons can be described by the Surface Complexation Model (SCM). We assumed that the adsorbent surface is strongly energetically heterogeneous and derived the adsorption isotherm using rectangular distribution of adsorption energy and condensation approximation for the local isotherm equation. Assuming additionally that the bulk concentration of divalent metal ion is low and does not change considerably during the adsorption process and next applying the Statistical Rate Theory of Interfacial Transport (SRT) we derived the Elovich equation—the experimental formula describing adsorption kinetics.
Keywords: Divalent metal ion; Adsorption kinetics; Oxides; Activated carbons; Statistical rate theory;
Kinetics and equilibrium of adsorption of organic solutes on mesoporous carbons by Adam W. Marczewski (5818-5826).
Static and kinetic studies on adsorption of nitrobenzene, 4-nitrophenol and 4-chlorophenol on two mesoporous carbons are performed. The carbon properties are analyzed by means of nitrogen adsorption. The adsorption experiments are performed in acidic buffer solutions in a wide range of concentrations. The static experiments are analyzed by means of Langmuir–Freundlich and Freundlich isotherms. The Lagergren, pseudo-second-order, intraparticle-diffusion and multi-exponent equations are used in the analysis of kinetic equilibria.
Keywords: Mesoporous carbon; Adsorption kinetics; Benzene derivatives;
Theoretical description of the kinetics of solute adsorption at heterogeneous solid/solution interfaces by Wladyslaw Rudzinski; Wojciech Plazinski (5827-5840).
One of these steps is the slowest and controls the rate of sorption. Depending on the assumption which of these steps is the rate-controlling one, a variety of equations have been proposed in literature to describe that kinetic step. The knowledge of the nature of that kinetic and its theoretical description are very crucial for practical applications, as a key to design the adsorption equipment and conditions for an optimum efficiency to be achieved.So, first some laboratory experimental tests and next their subsequent theoretical analyses are carried out to elucidate the nature of the rate-controlling kinetic process. Such studies may involve a variety of experiments whose time dependence of adsorption is the most fundamental information. Sometimes accompanying studies of the corresponding adsorption equilibria are also carried out, but it seems that the importance of these studies has not been sufficiently recognized.Only such combined study creates a chance to distinguish correctly between one and another kinetic model to be assumed. However, the most essential condition is using proper theoretical expressions to represent the features of some kind of kinetics. Here we will show how the above-mentioned conditions may affect distinguishing between the kinetics which is governed by the intraparticle diffusion, and that in which surface reactions control the rate of sorption in an adsorption system. This is because these two kinetic models are most frequently assumed in the theoretical interpretation of experimental kinetic data.
Keywords: Adsorption; Kinetics; Intraparticle diffusion; Surface reaction;
Time-resolved gas chromatography applied to submonolayer adsorption by E. Metaxa; T. Agelakopoulou; I. Bassiotis; S. Margariti; V. Siokos; F. Roubani-Kalantzopoulou (5841-5845).
The reversed-flow inverse gas chromatographic method was used to study the local adsorption parameters of the action of five hydrocarbons on one hand, namely, ethane, ethene, ethyne, propene and 1-butene and of ozone, on the other, on two known and widely used oxides, CaO and SiO2, respectively. Five physicochemical parameters concerning adsorption have been obtained for each of 20 heterogeneous systems studied, namely local adsorption energy, local adsorption isotherm, local monolayer capacity, probability density function for adsorption energies and energies from lateral interactions. Thus, the RF-IGC method is engaged to provide a new pathway for heterogeneous surface characterization, which is the basis of many scientific investigations and technological applications.
Keywords: Reversed-flow gas chromatography; Inverse gas chromatography; Hydrocarbon/oxide interface; Hydrocarbon-ozone/CaO interface; Hydrocarbon-ozone/SiO2 interface; Local adsorption quantities;
Molecular dynamics study of the equilibrium flux of gas molecules to a fractal/rough surface by T. Panczyk; T. Warzocha; W. Rudzinski (5846-5850).
The frequency of collisions of ideal gas molecules (argon) with a rough surface has been studied. The rough/fractal surface was created using the random deposition technique. By applying various depositions the surface roughness was controlled and, as a measure of irregularity, the fractal dimensions of the surfaces were determined. The surfaces were next immersed in ideal gas and the numbers of collisions with these surfaces were counted. The calculations were carried out using the simplified molecular dynamics simulation technique (only hard core repulsions were assumed). The calculations were performed for various ratios of gas phase atoms diameter to the surface substrate atoms diameter. The results obtained showed that the size of a gas phase atom has crucial influence on the relation between the frequency of collision and the surface fractal dimension
Keywords: Roughness; Fractal; Frequency of collisions; Adsorption kinetics; Geometric irregularity;
Isothermal adsorption kinetics on heterogeneous surfaces by Xinyu Xia; Raoul Naumann d’Alnoncourt; Jennifer Strunk; Sergey Litvinov; Martin Muhler (5851-5855).
Adsorption kinetics on energetically heterogeneous surfaces under isothermal conditions is analyzed using the uniform energy distribution model. Considering the quasi-equilibrium of surface diffusion between the adsorption sites with different energy, the kinetic equations d Θ / d t = ( k a p − A d K diff ) ( 1 − Θ ) for first-order adsorption and d Θ / d t = k a p ( 1 − Θ ) 2 − A d K diff Θ ( 1 − Θ ) for dissociative adsorption are obtained, where K diff is a coefficient describing the surface diffusion equilibrium, which depends on the coverage and the energy distribution. Under isochoric conditions with p decreasing due to adsorption, surface diffusion accelerates the rate towards equilibrium significantly, as observed in static calorimetric adsorption experiments. An approximate solution in Lagergren form is derived for this condition.
Keywords: Adsorption; Microkinetic analysis; Surface heterogeneity; Surface diffusion; Microcalorimetry;
Study of oscillations and pattern formation in the CO + O2 reaction on Pt(1 0 0) surfaces through dynamic Monte Carlo simulation by S.J. Alas; G. Zgrablich (5856-5863).
Oscillations and pattern formation driven by a surface reconstruction are studied for the catalytic oxidation of CO on Pt(1 0 0) single-crystal surfaces through dynamic Monte Carlo simulations at low pressure and relatively high temperatures conditions. Sustained, modulated, irregular and damped oscillations are observed in our analysis as well as the formation of cellular, target, double spiral, spiral wave and turbulent patterns. The effect and the importance of the hex ⇆ 1 × 1 surface phase transition and partial pressure of the reactants in the gas phase on the behavior of the system are discussed.
Keywords: CO oxidation; Kinetic oscillations; Pattern formation; Surface reconstruction; Dynamic Monte Carlo simulation;
Surface status and size influences of nickel nanoparticles on sulfur compound adsorption by Chang Hyun Ko; Jung Geun Park; Ji Chan Park; Hyunjoon Song; Sang-Sup Han; Jong-Nam Kim (5864-5867).
Metallic nickel nanoparticles were incorporated on mesoporous silica to remove sulfur compounds in diesel selectively. In the first method, nickel nanoparticles were formed on mesoporous silica SBA-15 by impregnation and subsequent reduction of nickel nitrate. The sulfur adsorption capacity was strongly dependent on the nickel loading and the average nickel particle size. In the second method, nickel nanoparticles were synthesized in solution in the presence of a capping agent and then incorporated in mesoporous silica MCF by sonication. Although these particles maintain their sizes on the MCF surface after heat treatment, capping agent remaining on the Ni particle surface might interfere the adsorption of sulfur compounds.
Keywords: Sulfur adsorption; Desulfurization; Nickel nanoparticle; Mesoporous silica;
Influence of pretreatment methods on adsorption and catalytic characteristics of toluene over heterogeneous palladium based catalysts by Wang Geun Shim; Sang Chai Kim; Hyun Chul Kang; Seung Won Nahm; Jae Wook Lee; Hee Moon (5868-5875).
The adsorption and catalytic characteristics of heterogeneous palladium based catalyst and its modified catalysts with gases (air and hydrogen) and acidic aqueous solution (HCl) were studied for evaluating the influence of pretreatment methods for toluene. The structural and energetic adsorption properties of the parent and pretreated catalysts were analyzed by means of nitrogen adsorption isotherms and gravimetric methods. The light-off curve and the XPS investigation were used for analyzing the catalytic activity and the surface state of palladium. It was clearly shown from the experimental results that hydrogen pretreated catalysts having metallic surface state exhibited the highest adsorption capacity and catalytic activity compared to that of parent and modified catalysts. The adsorption equilibrium data for toluene were obtained at three different temperatures and correlated successfully with the two-site Langmuir molecular isotherm model (L2m). It was also found that the palladium phase has more adsorption affinity for toluene molecules than the alumina support. The isosteric heat of adsorption calculated by using the Clausius–Clapeyron equation significantly changed with the coverage and the lateral interactions between the adsorbate–adsorbate molecules control the system. Furthermore, comparative analysis of the adsorption energy distribution revealed that the parent and its modified catalysts have different types of surface energetic heterogeneities.
Keywords: Adsorption; Catalytic oxidation; Palladium; Pretreatment; VOCs;
Intermittent temperature-programmed desorption study of perovskites used for catalytic purposes by F. Gaillard; J.P. Joly; A. Boréave; P. Vernoux; J.-P. Deloume (5876-5881).
A differential desorption technique, called intermittent temperature-programmed desorption (ITPD), was used to give new insights into the properties of La1−x Sr x Co0.8Fe0.2O3 perovskites as a contribution to improve their performances with respect to various important application fields such as catalysis, electrocatalysis and solid oxide fuel cells (SOFC). Both ITPD and interrupted TPD (carried out at different heating rates) evidenced two distinct oxygen adsorbed states, desorbing at temperatures lower than 400 °C, corresponding to less than 5% of a compact monolayer of oxide ions. The first one, for low desorption temperatures (lower than 290 °C) exhibits a heat of adsorption (ΔH) distribution from 101 to 121 kJ mol−1. The second one, for higher desorption temperatures (between 290 and 400 °C) corresponds to ΔH = 146 ± 4 kJ mol−1. Additionally, for temperatures higher than 400 °C, we observed a continuous desorption of oxygen species, probably originating from the sub-surface or semi-bulk, with an associated activation energy of desorption ≥175 kJ mol−1.
Keywords: Perovskite; Oxygen; Temperature-programmed desorption; ITPD;
Hydrogen and noble gas interactions with iron nano-flakes by A.J. Groszek (5882-5887).
Exposure of pure iron nano-flakes to hydrogen generates a high heat evolution associated with hydrogen uptakes shown by flow-through microcalorimetry. A large part of the hydrogen was found to be irreversibly absorbed by the iron flakes at 220 °C and atmospheric pressure, but an increased desorption of hydrogen was achieved by noble gases, such as helium and argon. Thus the iron surfaces displayed strong affinity for hydrogen, but also, surprisingly, for the noble gases, which were found to be able to displace hydrogen from the iron surfaces.The uptake of hydrogen by the iron flakes was observed to reach 9 wt.% after exposure for 5 h, which may be of interest in hydrogen storage applications. Desorption with the help of argon may provide an acceptable method of hydrogen recovery.
Keywords: Hydrogen; Noble gas; Nano-flakes; Flow-through Microcalorimetry;
Hydrogenolysis of methylcyclopentane over the bimetallic Ir–Au/γ-Al2O3 catalysts by R.J. Chimentão; G.P. Valença; F. Medina; J. Pérez-Ramírez (5888-5893).
The gas-phase hydrogenolysis of methylcyclopentane (MCP) was investigated over the bimetallic Ir–Au/γ-Al2O3 catalysts. The bimetallic systems containing the atomic Au/Ir ratios in the range of 0.125–8 and a fixed total metal content of 8 wt.%, were prepared by the sequential impregnation (SI) and co-impregnation (CI) methods. The corresponding monometallic Ir/γ-Al2O3 and Au/γ-Al2O3 catalysts were also prepared. The materials were characterized by ICP, XRD, N2 adsorption, TEM, and H2 chemisorption. Highly dispersed Ir nanoparticles were obtained in all cases, while the size of Au nanoparticles increased (up to 50 nm) upon the increasing Au content in the catalyst. The monometallic gold catalyst did not adsorb H2. The incorporation of Au increased the amount of irreversible adsorbed H2 in the Ir–Au/γ-Al2O3 catalysts with respect to the monometallic ones. The products obtained in the MCP hydrogenolysis were 2-methylpentane (2-MP), 3-methylpentane (3-MP) and n-hexane (n-H). The initial rate (molecules of MCP reacted s−1 gIr −1) increased with the Au content. The deactivation was lower for bimetallic catalysts, particularly for the CI ones. The addition of Au played a significant effect on chemisorption and catalytic properties of Ir.
Keywords: Bimetallic; Catalysts; Chemisorption; MCP; Hydrogen; Hydrogenolysis; Ir; Au;
Impact of potassium on the heats of adsorption of adsorbed CO species on supported Pt particles by using the AEIR method by Salim Derrouiche; Paul Gravejat; Badr Bassou; Daniel Bianchi (5894-5898).
The heats of adsorption at several coverages of the linear and bridged CO species (denoted L and B, respectively) adsorbed on the Pt0 sites of the 2.9 wt% Pt/10% K/Al2O3 catalyst are determined using the Adsorption Equilibrium Infrared spectroscopy method. The addition of K on 2.9% Pt/Al2O3 modifies significantly the adsorption of CO on the Pt particles: (a) the ratio L/B is decreased from 8.4 to 1, (b) a new adsorbed CO species is detected with an IR band at 1763 cm−1, (c) the heats of adsorption of L and B CO species are significantly altered and the positions of their IR bands are shifted. The heats of adsorption of L CO species are decreased: i.e. 206 and 105 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively. Two B CO species denoted B1 and B2, with different heats of adsorption are observed on Pt/K/Al2O3. The heats of adsorption of B2 CO species (major B CO species) are significantly larger than those measured in the absence of K: i.e. 94 and 160 kJ/mol at low coverages on Pt/Al2O3 and Pt/K/Al2O3 respectively, whereas those of B1 CO species (minor species) are similar: 90 kJ/mol at low coverages. These values are consistent with the qualitative High Resolution Electron Energy Loss Spectrometry literature data on Pt(1 1 1) modified by potassium.
Keywords: Adsorption Equilibrium Infrared spectroscopy; Potassium; Platinum; Heat of adsorption; Carbon monoxide;
On the mechanism of reactive adsorption of dibenzothiophene on organic waste derived carbons by C.O. Ania; J.B. Parra; A. Arenillas; F. Rubiera; T.J. Bandosz; J.J. Pis (5899-5903).
The mechanism of reactive adsorption of dibenzothiophene (DBT) on a series of modified carbons derived from the recycled PET was investigated. The influence of the oxygen functionalities of the adsorbent on the DBT adsorption capacity was explored. The results revealed that adsorption of DBT on activated carbons is governed by two types of contributions: physisorption on the microporous network of the carbons and chemisorption. Introduction of surface acidic groups enhanced the performance of the carbons as a result of their specific interactions with DBT. The nature of the acidic groups is a decisive factor in the selectivity of the reactive adsorption process.
Keywords: Desulfurization; Dibenzothiophene; Reactive adsorption; PET waste;
Variation of the vanadium oxidation state within a VPO catalyst layer in a membrane reactor: XPS mapping and modelling by Y. Suchorski; B. Munder; S. Becker; L. Rihko-Struckmann; K. Sundmacher; H. Weiss (5904-5909).
Recently, the feasibility of butane oxidation in an electrochemical membrane reactor (EMR) using a vanadium phosphorus oxide (VPO) catalyst layer on a tubular anodic electrode has been reported. This novel application of EMR gives rise to questions about the vanadium oxidation state (Vox) under working conditions and about its spatial distribution in the catalyst layer. It has now been determined by means of position-resolved XPS measurements. In addition, model calculations on the spatial Vox distribution have been performed for the first time. The simulations reveal a non-uniform 3D distribution of Vox due to the relative rate of reduction and re-oxidation processes in the catalyst layer, in good agreement with the experimental XPS data.
Keywords: VPO catalysts; Electrochemical membrane reactor; XPS; Modelling;
Spectroscopic studies of alumina-supported nickel catalysts precursors by S. Pasieczna-Patkowska; J. Ryczkowski (5910-5913).
Nickel alumina-supported catalysts were prepared from acidic solutions of nickel nitrate by the CIM and DIM methods (classical and double impregnation, respectively). The catalysts exhibited different nickel species due to the existence of various metal–support interaction strengths. As a consequence, the reducibility and other surface properties changed as a function of the preparation method. The aim of this work was to study the interaction between the metal precursor and the alumina surface by means of FT-IR (Fourier transform infrared) and FT-IR/PAS (FT-IR photoacoustic spectroscopy).
Keywords: Nickel catalysts; Alumina; Adsorption; FT-IR; FT-IR/PAS;
Etching reaction of methylchloride molecule on the GaAs (0 0 1)-2 × 4 surface by M. Ozeki; Y. Iwasa; Y. Shimizu (5914-5919).
Adsorption process of methylchloride (CH3Cl) on the GaAs (0 0 1)-2 × 4 surface was studied by a scanning tunnelling microscopy (STM) measurement. The arsenic rich 2 × 4 surface, which was prepared by molecular beam epitaxy (MBE), was exposed to a supersonic molecular beam of CH3Cl with a kinetic energy of 0.06 eV. New bright spots appeared on the CH3Cl exposed surface. They were largely observed at the “B-type” step edge and divided into two types according to their locations. It was suggested that new spots were due to weakly adsorbed CH3Cl molecules without any dissociation. The adsorption mechanism of CH3Cl molecule was also studied by an ab initio Hartree-Fock calculation, which explained the experimental results well.
Keywords: GaAs; Etching; Adsorption; STM; Hartree-Fock;
Evaluation of semiconducting sensor materials on the basis of catalytic test reaction by Wincenty Turek; Mieczyslaw Lapkowski; Agnieszka Krowiak; Helena Teterycz; Roman Klimkiewicz (5920-5924).
Oxidative–reductive properties on the acid–base surfaces of the oxide compositions Sn–Ce–Rh–O and Zr–Mg–Y–O, active as catalysts in the ketonization of secondary alcohols were determined based on the isopropanol conversion selectivity. The kinetics of isopropanol conversion was measured in the oxygen-free atmosphere. Activation energies for both directions of conversion (dehydration to propylene and dehydrogenation to acetone) were calculated. The results were compared with the kinetics over SnO2 and ZrO2. Both oxide compositions, Sn–Ce–Rh–O and Zr–Mg–Y–O are oxidative–reductive catalysts containing Lewis acid centers.
Keywords: Isopropanol; Dehydration; Dehydrogenation; Kinetics; Zirconium oxide; Cerium oxide; Tin oxide; Lewis acid centers;