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Applied Surface Science (v.256, #17)

Editorial Board (pp. ii).

Comments on the seventh international symposium “Effects of surface heterogeneity in adsorption and catalysis on solids” by Władysław Rudziński Guest Editor; Małgorzata Witko Guest Editor (pp. 5127-5130).

Adsorption and diffusion of argon confined in ordered and disordered microporous carbons by Joshua D. Moore; Jeremy C. Palmer; Ying-Chun Liu; Thomas J. Roussel; John K. Brennan; Keith E. Gubbins (pp. 5131-5136).

We use a combination of grand canonical Monte Carlo and microcanonical molecular dynamics simulations to study the adsorption and diffusion of argon at 77K and 120K confined in previously generated models of a disordered bituminous coal-based carbon, BPL, and an ordered carbon replica of Faujasite zeolite (C-FAU). Both materials exhibit a maximum in the diffusion coefficient as well as anomalous (sub-diffusive) behavior in the mean-squared displacements at short times at some relative pressures. In BPL, the anomalous diffusion occurs at low relative pressures, due to the trapping of argon atoms in small pores. In C-FAU, the anomalous diffusion occurs at high relative pressures, due to competitive diffusion of atoms traveling through windows and constrictions which interconnect the pores. All diffusion eventually tends to Fickian diffusion at longer times.

Keywords: Adsorption; Diffusion; Activated carbon; Carbon replica; Faujasite

Diffusion in heterogeneous lattices by A. Tarasenko; L. Jastrabik (pp. 5137-5144).

We present here the results of our investigations of particle diffusion over different heterogeneous lattices with deep and shallow adsorption sites. A general analytical expression for chemical diffusion coefficient has been derived for a number of inhomogeneous lattices of different dimensionality and symmetry. We have calculated coverage dependencies of diffusion coefficients. The analytical data have been compared with the numerical data obtained by the kinetic Monte Carlo simulations. Almost perfect agreement between the respective results has been found.

Keywords: Lattice-gas systems; Diffusion; MC simulations

Application of mixed order rate equations to adsorption of methylene blue on mesoporous carbons by A.W. Marczewski (pp. 5145-5152).

Static and kinetic studies on adsorption of methylene blue on four synthesized mesoporous carbons are presented. The carbon properties are analyzed by means of nitrogen adsorption. The static experiments are analyzed by means of Langmuir–Freundlich and Freundlich isotherms. The Lagergren, pseudo-second-order and mixed order as well as the multi-exponent equations are used in analysis of kinetic equilibria. The properties of rate equations are compared and analyzed.

Keywords: Mesoporous carbon; Adsorption kinetics; Rate equations; Methylene blue

A new empirical rate equation for adsorption kinetics at solid/solution interface by Saied Azizian; Rahimeh Naviri Fallah (pp. 5153-5156).

It has been shown that most of the previously reported empirical rate equations for kinetics of adsorption at the solid/solution interface show high relative errors at the initial times of adsorption. In the present work we made a modification onto pseudo-first-order and pseudo-second-order models and presented a new empirical rate equation, called the modified pseudo- n-order (MP nO) model. The results of fitting to the experimental data show that the MP nO model has low relative errors in the whole range of adsorption time.

Keywords: Kinetics; Adsorption; Empirical rate equation

Applicability of the film-diffusion model for description of the adsorption kinetics at the solid/solution interfaces by Wojciech Plazinski (pp. 5157-5163).

The adsorption kinetics at the solid/solution interfaces has been described by using the kinetic model based on accepting the existence of the concentration gradient in the region of bulk solution close to the solid surface (external film-diffusion model). This model has also been adopted to explain some behaviours observed in the real adsorption systems. Simultaneously, the pseudo-first order (Lagergren) equation can be derived applying this model. The results indicate that the necessary condition to state that the “diffusion across the liquid film” mechanism is involved in controlling the rate of adsorption process is the linearity of the initial parts of kinetic isotherms plotted as the amount adsorbed vs. the time. The two methods have been proposed to distinguish between this mechanism and the classical Langmuir kinetics. The results presented here might be useful in identifying if the concentration gradient in the bulk solution influences the overall adsorption rate.

Keywords: Sorption; Kinetics; External film diffusion; Pseudo-first order

Studies of adsorption equilibria and kinetics in the systems: Aqueous solution of dyes–mesoporous carbons by A. Derylo-Marczewska; A.W. Marczewski; Sz. Winter; D. Sternik (pp. 5164-5170).

Two carbonaceous materials were synthesized by using the method of impregnation of mesoporous silicas obtained by applying the Pluronic copolymers as pore-creating agents. The isotherms of adsorption of methylene blue and methyl orange from aqueous solutions were measured by the static method. The profiles of adsorbate concentration change in time were obtained from the UV–vis spectra. The adsorption isotherms and kinetic dependence were discussed in the terms of theory of adsorption on heterogeneous surfaces.

Keywords: PACS; 61.43.Gt; 67.70.+n; 82.70.−Dd; 82.70.−GgDye adsorption; Mesoporous carbons; Adsorption equilibria and kinetics

Surface heterogeneity effects of activated carbons on the kinetics of paracetamol removal from aqueous solution by B. Ruiz; I. Cabrita; A.S. Mestre; J.B. Parra; J. Pires; A.P. Carvalho; C.O. Ania (pp. 5171-5175).

The removal of a compound with therapeutic activity (paracetamol) from aqueous solutions using chemically modified activated carbons has been investigated. The chemical nature of the activated carbon material was modified by wet oxidation, so as to study the effect of the carbon surface chemistry and composition on the removal of paracetamol. The surface heterogeneity of the carbon created upon oxidation was found to be a determinant in the adsorption capability of the modified adsorbents, as well as in the rate of paracetamol removal. The experimental kinetic data were fitted to the pseudo-second order and intraparticle diffusion models. The parameters obtained were linked to the textural and chemical features of the activated carbons. After oxidation the wettability of the carbon is enhanced, which favors the transfer of paracetamol molecules to the carbon pores (smaller boundary layer thickness). At the same time the overall adsorption rate and removal efficiency are reduced in the oxidized carbon due to the competitive effect of water molecules.

Keywords: Adsorption kinetics; Pharmaceuticals; Aqueous solution

Mechanism and kinetics of lithium vapor capture in a high-temperature packed bed of kaolinite by H.-C. Yang; H.-C. Eun; Y.-Z. Cho; H.-S. Lee (pp. 5176-5181).

This study investigated the characteristics of high-temperature lithium vapor-capturing reaction in a packed bed of calcined kaolin particles. The packed-bed sorption experiments were carried in the a temperature range of 700–900°C. The high-temperature reaction between LiCl vapor and calcined kaolin sorbent generated lithium aluminum silicate (Li₂O·Al₂O₃·2SiO₂). An increase in kaolin bed temperature results in an increase in lithium-capturing rate, but it has no effect on the maximum lithium uptake. The resistance of LiCl vapor diffusion into the pores of calcined kaolin particles was negligible, and the chemical reaction at the kaolin surface controlled the overall sorption reaction rates by up to 60% of metakaolinite conversion. The order of the reaction between metakaolinite and LiCl vapor was determined as 1.94 and its activation energy was estimated as 7.95kcal/mol according to the Arrhenius relationship.

Keywords: Lithium; Kaolinite; High temperature; Volatile metal capture

Effect of outgassing temperature on the performance of porous materials by Alessandro Figini-Albisetti; Leticia F. Velasco; José B. Parra; Conchi O. Ania (pp. 5182-5186).

This work illustrates the consequences of an inadequate outgassing temperature of porous materials of different nature (zeolites and activated carbons) on their performance on gas storage and wastewater remediation. Outgassing at low temperature in thermally stable materials leads to an incomplete cleaning of the porous surface; as a result, the gas storage ability based on adsorption isotherms is underestimated. In contrast, outgassing at elevated temperature in temperature-sensitive materials provokes irreversible changes in their composition and structure, which also affects strongly their stability and performance. Two examples illustrating wrong interpretation data on CO₂ capture on zeolites and wastewater treatment using activated carbons are addressed. The results show how the performance of a given material can be significantly modified or misunderstood after the outgassing pretreatment.

Keywords: Porous materials; Outgassing temperature; Gas adsorption; Wastewater treatment

Adsorption and structural properties of soft-templated mesoporous carbons obtained by carbonization at different temperatures and KOH activation by Joanna Górka; Aleksandra Zawislak; Jerzy Choma; Mietek Jaroniec (pp. 5187-5190).

Two series of phenolic resin-based mesoporous carbons were prepared by soft-templating strategy, which involves the formation of thermosetting carbon precursor by polymerization of phloroglucinol and formaldehyde in hydrophilic mesodomains of a thermally decomposable triblock copolymer used as a soft-template. It was shown that the volumes of mesopores and micropores in the resulting carbons can be tuned by varying carbonization temperature of phenolic resins in the range from 400 to 1000°C followed by the post-synthesis KOH activation at 700°C. The highly microporous carbons were obtained by KOH activation of phenolic resins pyrolyzed at lower temperature (∼500°C), while high temperature KOH activation (∼800°C) afforded microporous carbons with preserved mesoporosity.

Keywords: Mesoporous carbons; Soft-templating synthesis; KOH activation; Adsorption; Microporosity

Characterization of PSD of activated carbons by using slit and triangular pore geometries by D.C.S. Azevedo; R.B. Rios; R.H. López; A.E.B. Torres; C.L. Cavalcante; J.P. Toso; G. Zgrablich (pp. 5191-5197).

A mixed geometry model for activated carbons, representing the porous space as a collection of an undetermined proportion of slit and triangular pores, is developed, evaluated theoretically and applied to the characterization of a controlled series of samples of activated carbon obtained from the same precursor material. A method is proposed for the determination of the Pore Size Distribution (PSD) for such a mixed geometry model, leading to the unique determination of the proportion of pores of the two geometries fitting adsorption data. By using the Grand Canonical Monte Carlo (GCMC) simulation method in the continuum space, families of N2 adsorption isotherms are generated both for slit and triangular geometry corresponding to different pore sizes. The problem of the uniqueness in the determination of the PSD by fitting an adsorption isotherm using the mixed geometry model is then discussed and the effects of the addition of triangular pores on the PSD are analyzed by performing a test where the adsorption isotherm corresponding to the known PSD is generated and used as the “experimental” isotherm. It is found that a pure slit geometry model would widen the PSD and shift it to smaller sizes, whereas a pure triangular geometry model would produce the opposite effect. The slit and triangular geometry families of isotherms are finally used to the fit experimental N₂ adsorption data corresponding to a family of activated carbons obtained from coconut shells through a one-step chemical activation process with phosphoric acid in air, allowing for the determination of the micropore volume, the proportion of slit and triangular pores and the PSD corresponding to the mixed geometry. The same experimental data were fit using both the conventional slit pore model and the mixed geometry model. From the analysis of the effect of different preparation procedures on the resulting PSDs, it is concluded that the proposed mixed geometry model may probably better capture the morphology and energetics of activated carbons prepared by chemical activation under mild temperatures.

Keywords: PSD; Activated carbon; Phosphoric acid; Mixed geometry; Triangular pores

Studies on adsorption energy distributions computation from adsorption isotherms by the ansatz method by Steffen Arnrich; Grit Kalies; Peter Bräuer (pp. 5198-5203).

Since the well-knownadsorptionintegralequation (AIE) is an ill-posed problem, calculation of relevant energetic properties from gas and liquid adsorption isotherms on porous solids still remains a challenging field of research. There are two approaches for solving the AIE: (1) the numerical regularization method and (2) the fitting of the experimental adsorption data by functions possessing an analytical solution. Up to now the latter approach has been treated without consideration of the ill-posedness. The inclusion of ill-posedness in the approach leads to its specification which we call the ansatz method. By showing that a certain class of ansatz functions cannot be used for describing the total isotherms, we were urged to consider more general solutions being connected with the Stieltjes integrals. After applying a general inversion formula we can restrict the theoretically possible total isotherms and outline a feasible general ansatz.

Keywords: Adsorption integral equation; Gas and liquid adsorption; Ill-posedness; Stieltjes integral and transform; Ansatz method

BET surface area of carbonaceous adsorbents—Verification using geometric considerations and GCMC simulations on virtual porous carbon models by Piotr A. Gauden; Artur P. Terzyk; Sylwester Furmaniak; Peter J.F. Harris; Piotr Kowalczyk (pp. 5204-5209).

The applicability of BET model for calculation of surface area of activated carbons is checked by using molecular simulations. By calculation of geometric surface areas for the simple model carbon slit-like pore with the increasing width, and by comparison of the obtained values with those for the same systems from the VEGA ZZ package (adsorbate-accessible molecular surface), it is shown that the latter methods provide correct values. For the system where a monolayer inside a pore is created the ASA approach (GCMC, Ar, T=87K) underestimates the value of surface area for micropores (especially, where only one layer is observed and/or two layers of adsorbed Ar are formed). Therefore, we propose the modification of this method based on searching the relationship between the pore diameter and the number of layers in a pore. Finally BET; original and modified ASA; and A, B and C-point surface areas are calculated for a series of virtual porous carbons using simulated Ar adsorption isotherms (GCMC and T=87K). The comparison of results shows that the BET method underestimates and not, as it was usually postulated, overestimates the surface areas of microporous carbons.

Keywords: Computer simulation; GCMC; Virtual Porous Carbon; Surface area; BET

Influence of elastic strains on the adsorption process in porous materials. Thermodynamics and experiment by A. Grosman; C. Ortega (pp. 5210-5215).

If we disregard the shape of the boundary hysteresis loop, H1 for SBA-15, MCM-41 and KIT-6, H2 for p⁺-type porous silicon and porous glass, the hysteretic features inside the loop are qualitatively the same for all these systems and show that none of them are composed of independent pores whether the pores are interconnected or not. We hence believe that the physical parameter which couples the pores is not the interconnectivity but the elastic deformation of the porous matrix. The thermodynamic approach we develop includes the elastic energy of the solid. We show that the variation of the surface free energy, which is proportional to the deformation of the porous matrix, is an important component of the total free energy. With porous silicon, we experimentally show that a stress external to the porous matrix exerted by the substrate on which it is supported significantly increases the total free energy and the adsorbed amount and decreases the condensation pressure compared to that of the same porous matrix detached from its substrate which is the relaxed state of the supported layer. This stress can be partly relaxed by making thicker porous layers due to the breaking of Si–Si bonds. This results in the shift of the isotherms towards that of the membrane. We propose a new interaction mechanism occurring through the pore wall elastic deformation in which the external mechanical stress is imposed on a given pore by its neighbours.

Keywords: Porous material; Adsorption; Capillary condensation; Elastic strain

Nanostructured carbons for solid phase extraction by A.M. Puziy; O.I. Poddubnaya; B. Gawdzik; M. Sobiesiak; C.A. Reinish; M.M. Tsyba; T.P. Segeda; M.I. Danylenko (pp. 5216-5220).

Nanostructured carbons have been obtained by the template method using zeolite NaY and silica gels (SG60, Fluka and ZK, POCh) as structure directing agents. Texture and porous structure of carbons were characterized by TEM, XRD and nitrogen adsorption. Surface chemistry was investigated by the potentiometric titration method. It has been shown that all carbons show developed and uniform porous structure with mean size in the micropore range (1.1nm) for zeolite derived carbon and in the mesopore range (3.4 and 4.8nm) for silica gel derived carbons. The BET surface area of silica gel derived carbons is in the range 1230–1280m²/g whereas zeolite derived carbon possesses very high BET surface area, 3000m²/g. Potentiometric titration showed that carbons obtained by the template method contain significant amount of acid surface groups (carboxylic, lactone/enol and phenolic) with the total amount 1.1–1.5mmol/g. To study adsorption–desorption properties of nanostructured carbons towards phenol and chlorophenols the solid phase extraction method was used. High recoveries of chlorophenols were obtained (80–93%) at the breakthrough volumes 1700–3000mL. The recoveries are much higher than that obtained with commercially available carbon ACC (Supelco).

Keywords: Nanostructured carbon; Template method; Porous structure; Surface chemistry; Solid phase extraction

Carbon molecular sieves from carbon cloth: Influence of the chemical impregnant on gas separation properties by G. Rodríguez-Blanco; L. Giraldo; J.C. Moreno-Piraján (pp. 5221-5225).

Carbon materials with molecular sieve properties (CMS) were prepared by pyrolysis of cotton fabrics by chemical activation procedures. To evaluate the changes in the chemical and textural properties, the impregnants AlCl₃, ZnCl₂ and H₃PO₄ were used at 1123K. The materials were characterized using adsorption of nitrogen and carbon dioxide, TPD, and immersion calorimetry in C₆H₆. Adsorption kinetics of O₂, N₂, CO₂, CH₄, C₃H₈ and C₃H₆ were measured in all the prepared materials to determine their behaviour as molecular sieves. The results confirm that the chemical used as impregnant has a significant effect on the resulting CMS separation properties. All materials exhibit microporosity and low oxygen surface group contents; however, the sample impregnated with zinc chloride, with an immersion enthalpy value of 66.4Jg⁻¹ in benzene, exhibits the best performance in the separation of CH₄–CO₂ and C₃H₈–C₃H₆ at 273K.

Keywords: Activated carbon cloth; Microporous material; Chemical activation; Immersion calorimetry; Molecular sieve; Gas separation

Grand canonical Monte Carlo simulations of hydrogen adsorption in carbon cones by A. Gotzias; H. Heiberg-Andersen; M. Kainourgiakis; Th. Steriotis (pp. 5226-5231).

The Monte Carlo method in its grand ensemble variant (GCMC) is used in order to study the hydrogen adsorption (77K) characteristics of novel carbon structures, namely Carbon Cones (CCs). CCs are conical shaped curved graphitic sheets, with five different apex angles. CC structures with correct bonding topology were developed via atomistic-molecular simulations, while GCMC simulations of hydrogen adsorption were carried out on the five different apex angle structures. Emphasis has been given on the adsorption properties inside the cones and it was found that cone tips are characterized by enhanced adsorbability. The results were also compared with similar calculations on carbon nanotubes.

Keywords: PACS; 81.05.Rm; 82.20.Wt; 61.43.Gt; 68.43.−hCarbon cones; H; ₂; adsorption; GCMC simulations

Preparation and ozone-surface modification of activated carbon. Thermal stability of oxygen surface groups by J. Jaramillo; P.M. Álvarez; V. Gómez-Serrano (pp. 5232-5236).

The control of the surface chemistry of activated carbon by ozone and heat treatment is investigated. Using cherry stones, activated carbons were prepared by carbonization at 900°C and activation in CO₂ or steam at 850°C. The obtained products were ozone-treated at room temperature. After their thermogravimetric analysis, the samples were heat-treated to 300, 500, 700 or 900°C. The textural characterization was carried out by N₂ adsorption at 77K, mercury porosimetry, and density measurements. The surface analysis was performed by the Bohem method and pH of the point of zero charge (pH_pzc). It has been found that the treatment of activated carbon with ozone combined with heat treatment enables one to control the acidic–basic character and strength of the carbon surface. Whereas the treatment with ozone yields acidic carbons, carbon dioxide and steam activations of the carbonized product and the heat treatment of the ozone-treated products result in basic carbons; the strength of a base which increases with the increasing heat treatment temperature. pH_pzc ranges between 3.6 and 10.3.

Keywords: Cherry stones; Activated carbon; Ozone treatment; Oxygen surface groups; Thermal stability

Factors affecting the adsorption of trichloroethylene onto activated carbons by A. Erto; R. Andreozzi; A. Lancia; D. Musmarra (pp. 5237-5242).

In this work, an experimental study aimed at the assessment of the factors affecting the adsorption of trichloroethylene (TCE) from water solutions onto activated carbons is presented. The influence of sorbent properties, such as B.E.T. surface area, micropore volume, chemical composition and acid/basic surface functional groups on TCE adsorption capacity is experimentally assessed by testing a set of 12 sorbents. Moreover, the effect of the presence of other species in solution, such as sodium acetate and tetrachloroethylene (PCE), is studied through parametric TCE adsorption isotherms realization. The experimental results show that the TCE adsorption capacity is promoted by a high B.E.T. surface area, micropore volume and C content and it is significantly affected by the presence of a non-ionic compound of similar structure (PCE), however it does not depend on the presence of an organic salt (sodium acetate). These results confirm that neither TCE–carbon ionic interaction nor sorbent ionization phenomena are involved in the TCE adsorption, since its mechanism is based on dispersion forces (London–Van Der Walls interaction). A thorough analysis of the experimental data set suggests that, in consideration of the TCE adsorption mechanism, the maximization of basal plane extent (as the B.E.T. surface area) and its effective fraction (as the C content) is a valid criterion to select or synthesize a new suitable sorbent for TCE adsorption from waters.

Keywords: Adsorption; Activated carbon; B.E.T. surface area; Micropore volume; Surface functional groups

Application of clustering based gas adsorption models to analysis of microporous structure of carbonaceous materials by Jan T. Duda; Mirosław Kwiatkowski; Janina Milewska-Duda (pp. 5243-5248).

The paper presents the results of research on possible application of an original clustering based mathematical description of gas adsorption processes to analysis of microporous structures of activated carbons. The LBET class model used is based on the classical BET approach to the multilayer adsorption process modelling, but it takes into account geometrical restrictions for the clusters size and a geometrical and energetic heterogeneity of surface. The effects of adhesive forces on the creation of second and higher layers are handled explicitly. An original fluid state model is used to make calculations possible for gas adsorption isotherms. Fitting of the LBET model to the empirical data is proposed to detect active constraints for multilayer adsorption and so to get information on the structure of micropores. Application of the formulae to the analysis of nitrogen and methane isotherms on an active carbon is discussed.

Keywords: Mathematical modelling of adsorption; Microporous structures; Fluid state equation

Synthesis of carbon-encapsulated nickel nanoparticles by U. Narkiewicz; M. Podsiadły (pp. 5249-5253).

Carbon-encapsulated metal nanoparticles (CEMNs) were obtained by the catalytic decomposition of hydrocarbons (CH₄, C₂H₆, C₂H₄) on nanocrystalline nickel. Nanocrystalline nickel was obtained by precipitation from nickel nitrate solution, followed by calcination and reduction under hydrogen. A small amount of structural promoters (aluminium and calcium oxide) was added to avoid recrystallisation of fine nickel particles at elevated temperatures. Reduction and carburisation of the samples was carried out in a differential reactor with mass control. The rate of decomposition of methane, ethane and ethylene on nanocrystalline nickel was measured and the apparent activation energy of the process was determined. The obtained samples were characterised using the XRD, SEM and HRTEM methods.

Keywords: Carbon nanocapsules; Nanocrystalline nickel; Carbon-encapsulated nanometals

Role of activated carbon features on the photocatalytic degradation of phenol by Leticia F. Velasco; José B. Parra; Conchi O. Ania (pp. 5254-5258).

In this work we have investigated the role of porous carbon material used as a photocatalyst and a catalyst support in the carbon/titania composite in the photodegradation of phenol, and compared the results to those of bare titanium oxide. The immobilization of titania on an activated carbon provoked acceleration of the degradation rate under UV irradiation, which is likely to be attributed to the porosity of the carbon support. The identification of the degradation intermediates detected in the solution showed that the presence of the carbon support affects the nature of phenol degradation mechanism through the formation of different intermediates. Additionally, phenol photodecomposition rate over the carbon support outperformed that attained in the carbon/titania composite, suggesting an important self-photoactivity of the carbon support.

Keywords: Photodegradation; Phenol; Activated carbon; Composite

Variable-temperature FT-IR studies on the thermodynamics of carbon dioxide adsorption on a faujasite-type H-Y zeolite by C. Otero Areán; M. Rodríguez Delgado (pp. 5259-5262).

Adsorption of carbon dioxide on a faujasite-type H-Y zeolite (Si:Al=2.6:1) was studied by variable-temperature (200–290K range) infrared spectroscopy. Adsorbed CO₂ molecules interact with the Brønsted acid Si(OH)Al groups located inside the zeolite supercage, bringing about a characteristic bathochromic shift of the O–H stretching mode from 3645cm⁻¹ (free OH group) to 3540cm⁻¹ (hydrogen-bonded CO₂ adsorption complex). Simultaneously, the asymmetric ( ν₃) mode of adsorbed CO₂ is observed at 2353cm⁻¹. From the observed variation of the integrated intensity of the 3645 and 2353cm⁻¹ IR absorption bands upon changing temperature, corresponding values of standard adsorption enthalpy and entropy were found to be Δ H°=−28.5(±1)kJmol⁻¹ and Δ S°=−129(±10)Jmol⁻¹K⁻¹. Comparison with the reported values of Δ H° for CO₂ adsorption on other zeolites is briefly discussed.

Keywords: Adsorption enthalpy; Adsorption entropy; Carbon dioxide; Infrared spectroscopy; Zeolites

Morphological, structural and adsorption features of oxide composites with silica and titania matrices by V.M. Gun’ko; V.M. Bogatyrev; M.V. Borysenko; M.V. Galaburda; I.Y. Sulim; L.V. Petrus; O.M. Korduban; E.V. Polshin; Ya.V. Zaulychnyy; M.V. Karpets; O.O. Foya; I.F. Myronyuk; V.L. Chelyadyn; U.Ya. Dzhura; R. Leboda; J. Skubiszewska-Zięba; J.P. Blitz (pp. 5263-5269).

Morphological, structural, electronic, and adsorption characteristics of complex oxides such as fumed silica/alumina and silica/titania, fumed silica with deposited oxides of Mg, Ti, Mn, Ni, Cu, Zn and Zr, silica gel with grafted ZrO₂, sol–gel titania doped by 3d-metals (Cr, Fe, Mn, V) were compared using adsorption, TEM, AFM, XRD, XPS, Mössbauer and Raman spectroscopy data. It was shown that surface, volume, and phase compositions of oxides, particle size distributions (5nm–3μm), specific surface area ( S_BET∼50–500m²/g), and porosity ( V_P∼0.1–2cm³/g) affected by synthesis technique and subsequent treatment determine electronic structure (bandgap, valence band and core levels structure) of the materials, adsorption of molecules and metal ions as well as other characteristics.

Keywords: PACS; 61.43.Gt, 61.46.Df, 61.46.Hk, 61.10.Nz, 68.47.GhFumed oxides; Silica gel; Titania; Alumina; Oxide deposits; Dopants; Structural and adsorption characteristics; Electronic structure; Nonuniformity

Influence of structural heterogeneity of nanoporous sorbent walls on hydrogen storage by B. Kuchta; L. Firlej; Sz. Roszak; P.Pfeifer; C. Wexler (pp. 5270-5274).

Heterogeneity is an ubiquitous aspect of adsorption, often modifying substantially the observed behaviour of the adsorbate–adsorbent system. In this paper, the influence of heterogeneity is explicitly analyzed for the case of the adsorption of molecular hydrogen onto nanoporous carbon. Grand Canonical Monte Carlo simulations were used to study the mechanism of adsorption in the models of the adsorbate that include both energetic and structural modifications of graphene-based slit pores. In particular, a partial substitution of carbons by boron modifies both the symmetry of the energy landscape and the strength of hydrogen physisorption; which results in considerable increases of the amount of adsorbed gas without major modification of the mechanism of adsorption. Additional heterogeneity arises from structural modifications of the adsorbent by neutron irradiation of boron-doped samples, where the boron fission products generate additional surface area for adsorption. Simulations of adsorption in such pores show that hydrogen uptake is strongly dependent on the chemical nature of the modified pore walls.

Keywords: Hydrogen; Adsorption; Boron; Computer simulations

Nonuniformity of starch/nanosilica composites and interfacial behaviour of water and organic compounds by V.M. Gun’ko; V.V. Turov; V.N. Barvinchenko; A.A. Turova; A.A. Rugal; V.I. Zarko; R. Leboda (pp. 5275-5280).

Hydrated starch alone and in composition with nanosilica A-300 and quercetin (natural antioxidant) was studied in the form of powders (mechanical mixture) and gels using¹H NMR (at 200–280K), FTIR (293K), TG (293–573K), TSDC (90–265K) and quantum chemistry methods. Influence of weakly polar (chloroform-d, CDCl₃) and polar ((CD₃)₂SO, DMSO) deuterated solvents on bound water structure in these systems was also analysed at 200–280K. The energetic and structural boundaries between weakly (unfrozen at 250–260< T<273K) and strongly (unfrozen at 200

Keywords: Fumed silica; Starch; Quercetin; Bound water; Interfacial behaviour; NMR

Hydrogen adsorption on the faujasite-type zeolite Mg–X: An IR spectroscopic and thermodynamic study by G. Turnes Palomino; C. Otero Areán; M.R. Llop Carayol (pp. 5281-5284).

Hydrogen adsorption (physisorption) on the faujasite-type zeolite Mg–X was studied by means of variable-temperature (80–140K) FT-IR spectroscopy. Perturbation of the adsorbed H₂ molecules by the cationic adsorbing centres of the zeolite renders the H–H stretching mode IR active, at 4065cm⁻¹. Simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, for a series of spectra recorded at the increasing temperature, allowed standard adsorption enthalpy and entropy to be determined. They resulted to be Δ H⁰=−13kJmol⁻¹ and Δ S⁰=−114Jmol⁻¹K⁻¹, respectively. Both, spectroscopic and thermodynamic results are discussed in the broader context of corresponding data for hydrogen adsorption on other alkali and alkaline-earth cation exchanged zeolites, showing that, while an approximate correlation exists between Δ H⁰ and H–H stretching frequency, deviations can be expected for the case of zeolites containing small metal cations.

Keywords: Adsorption enthalpy; Adsorption entropy; Hydrogen; Infrared spectroscopy; Zeolites

Monolayer aspects of high-resolution α_s-plots by Piotr A. Gauden (pp. 5285-5291).

The problem of the estimation of high resolution comparative plots ( α_s method) is revised. Adsorption isotherms of Ar ( T=87K) are simulated (GCMC) on the bundles of closed and opened multiwalled carbon nanotubes. Those materials are chosen in order to observe the influence of porosity on Ar adsorption, and consequently, on the comparative plots. The introduction of the structural heterogeneity (defects in the external and internal walls of osculating and separated nanotubes) is also studied. The monolayer and multilayer parts of adsorption are extracted from the total amount adsorbed for all studied adsorbents and the reference one (the bundle of the ideal 3-layered carbon tubes with very wide diameters). The significant influence of the distance between carbon nanotubes and defects (in the external and internal walls) is observed on the monolayer α_s-plots. In the case of comparative plots calculated for the multilayer adsorption the differences are also visible; however, the expected linear dependence of the amount adsorbed on a porous solid plotted against the amount adsorbed on a reference nonporous solid (the layer-by-layer adsorption occurs on both solid surfaces) in a wide range of relative pressures is not observed. The obtained results demonstrate the complexity of α_s method when both microporosity and surface heterogeneity are present. A comparison of isotherms shows that for the studied adsorbents Ar is sensitive to the appearance of the geometrical and structural defects, even at low coverage.

Keywords: Computer simulation; GCMC; Monolayer adsorption; α; _s; -plots

Experimental and simulated propene isotherms on porous solids by M.V. Navarro; B. Puértolas; T. García; R. Murillo; A.M. Mastral; F.J. Varela-Gandía; D. Lozano-Castelló; D. Cazorla-Amorós; A. Bueno-López (pp. 5292-5297).

The lack of treatment capacity of hydrocarbons by three-way catalysts during the “cold start” period creates an important environmental problem. During this period, the temperature of the three-way catalyst is too low for effective operation and cannot convert the hydrocarbons in the exhaust. 50–80% of the total hydrocarbon emissions are produced in this phase that accomplishes the first 60–120s of the engine operation. In this study, the technology chosen to treat these emissions is the use of HC-traps, and molecular simulations are tested as a tool to reproduce the experimental adsorption behaviour of porous solids. Therefore, experimental and simulated adsorption isotherms of propene (model hydrocarbon) have been obtained for four different crystalline materials with distinctive framework structures (3D and 1D) and a variety of Si/Al ratios and cations (three zeolites: ZSM-5, BETA and Mordenite; and a silicoaluminophosphate molecular sieve: SAPO-5).

Keywords: Hydrocarbon emission reduction; Propene trap; Silicoaluminophosphate; Zeolite; Cold start; Molecular simulation

The simplest model of adsorption of molecules with different orientations in adlayer on the stepped surface by V.F. Fefelov; V.A. Gorbunov; A.V. Myshlyavtsev; M.D. Myshlyavtseva; S. Evseeva (pp. 5298-5304).

In this article we have constructed and studied using the Monte Carlo and transfer-matrix techniques the simple lattice gas models of self-assembled monolayer, which consists of molecules with different orientations in the adlayer on the stepped surfaces. It was shown that in the case of adsorption of complex molecules the surface heterogeneity of stepped type leads to a great variety of ordered structures comparatively with homogeneous one. The constructed models fairly well reproduce the main features of real SAMs consisting of molecules with different orientations with respect to interface and the model ordered phases are also analogues to the structures of real SAMs.

Keywords: Self-assembled monolayer; Monte Carlo method; Adsorption; Dimer; Different orientations

Evaluation of confinement effects in zeolites under Henry's adsorption regime by Marc Pera-Titus; Joan Llorens (pp. 5305-5310).

This paper provides a detailed thermodynamic analysis of gas/vapour adsorption in zeolites at low pressures. At these conditions, we show first that Henry's isotherm can be conveniently rewritten using the thermodynamic isotherm model developed in a previous study [J. Llorens, M. Pera-Titus, Description of gas adsorption on microporous materials: evaluation of energy heterogeneity, J. Colloid Interface Sci. 331, 2009, 302–311], linking the integral free energy of adsorption relative to saturation, Ψ/ RT, expressed as a Kiselev integral, with the variable Z=1/−ln( Π), being Π the relative pressure. Relevant information about sorbate confinement effects in zeolites can be inferred using strong sorbates under Henry's adsorption regime using the thermodynamic formulation provided here. The confining level of zeolites can be characterized by a parameter ( m₁), whose value depends on the zeolite framework, but remains essentially unchanged with the sorbate probe molecule and temperature. We illustrate the application of these concepts using a collection of MFI and MTW-type zeolites as model systems.

Keywords: Zeolite; Confinement; Energy heterogeneity; Thermodynamic isotherm; Gas adsorption

Studies of intrawall porosity in the hexagonally ordered mesostructures of SBA-15 by small angle X-ray scattering and nitrogen adsorption by Stanislaw Pikus; Ewa B. Celer; Mietek Jaroniec; Leonid A. Solovyov; Maciej Kozak (pp. 5311-5315).

Ordered mesoporous silicas (OMSs) such as SBA-15 ( p6 mm symmetry group) synthesized in the presence of block copolymers containing poly(ethylene oxide) blocks possess irregular complementary pores in the walls of ordered mesopores. The X-ray scattering caused by this complementary porosity contributes to the background of the SAXS patterns. This work shows the possibility of using the SAXS data for the study of intrawall channels interconnecting ordered cylinders in SBA-15. The proposed SAXS analysis was tested by using a series of SBA-15 samples obtained at different temperatures of hydrothermal treatment (from 60 to 180°C). The structural modelling of the SAXS patterns recorded for a series of SBA-15 samples was performed by using the continuous density function (CDF) technique in combination with the derivative difference minimization (DDM) method of full-profile refinement. This method is well suited for extraction of the background curves from the SAXS patterns. The resulting smooth background curves were analyzed by the well-known method in the SAXS theory used for evaluation of heterogeneity distributions, which in this case characterize the intrawall complementary porosity. A relatively good agreement has been observed between the data obtained by SAXS and nitrogen adsorption analysis. The SAXS analysis is sufficiently sensitive for examination of heterogeneous microporosity in SBA-15 materials. The average diameter of intrawall pores for the SBA-15 sample obtained at 60°C was only about 1.4nm. However, this diameter increased with the increasing temperature of hydrothermal treatment; namely, it was 1.5, 1.8, 2.6, 2.6, 3.5 and 5.2nm for the SBA-15 samples hydrothermally treated at 80, 100, 120, 140, 160 and 180°C, respectively.

Keywords: SAXS; Adsorption; SBA-15; Intrawall porosity; Structure characterization

Free volumes evolution during desorption of n-heptane from silica with regular pore geometry. Positron annihilation study by J. Goworek; R. Zaleski; W. Buda; A. Kierys (pp. 5316-5322).

The mechanism of n-heptane evaporation from mesoporous MCM-41 silica was investigated by positron annihilation lifetime spectroscopy (PALS). Experiments were performed in situ during desorption of hydrocarbon under stepwise lowered pressure. Desorption is a quasicontinuous process that corresponds to emptying various types of free volumes in the silica/ n-heptane system, including mesopores. Insight into the kinetics of desorption was derived from the changes of PALS spectra associated with succeeding stages of pore emptying. For the investigated system emptying of pores and formation of bubbles in the n-heptane condensate present in regular pores were found to take place at various bulk saturating vapour pressure of the fluid.

Keywords: PALS; MCM-41; n; -Heptane desorption

CO₂ adsorption on branched polyethyleneimine-impregnated mesoporous silica SBA-15 by R. Sanz; G. Calleja; A. Arencibia; E.S. Sanz-Pérez (pp. 5323-5328).

Adsorption of pure CO₂ on SBA-15 impregnated with branched polyethyleneimine (PEI) has been studied. Materials were prepared by impregnating the pore surface of SBA-15 mesoporous silica with different amounts of branched PEI (10, 30, 50 and 70wt%). Textural properties, elemental analysis and low angle XRD measurements of the prepared samples showed a progressive pore filling of SBA-15 as PEI loading was increased. Pure CO₂ adsorption isotherms on these modified SBA-15 materials were obtained at 45°C, showing high adsorption efficiency for CO₂ removal at 1bar. Chemisorption of CO₂ on amino sites of the modified SBA-15 seems to be the main adsorption mechanism. PEI content of impregnated SBA-15 influences the adsorption capacity of the material, being a relevant variable for CO₂ removal by adsorption. Temperature effect on adsorption was also studied in the range 25–75°C, showing that temperature strongly influences CO₂ adsorption capacity. Adsorption capacity was also tested after regeneration of the PEI-impregnated SBA-15 materials. Our results show that these branched PEI-impregnated materials are very efficient even at low pressure and after several adsorption–regeneration cycles.

Keywords: Mesoporous silica; SBA-15; Polyethyleneimine; Amino group; Carbon dioxide removal; CCS

Determination of the spatial distribution of multiple fluid phases in porous media by ultra-small-angle neutron scattering by M. Kainourgiakis; Th. Steriotis; G. Charalambopoulou; M. Strobl; A. Stubos (pp. 5329-5333).

In the present work contrast-matching USANS (ultra-small-angle neutron scattering) was employed in order to determine the spatial distribution of immiscible fluids confined within a macroporous α-Al₂O₃ membrane. Water-air as well as water-hydrocarbon and hydrocarbon-air systems were examined and the analysis of the results, also on the basis of a complementary numerical study provided significant information on the behaviour of the multiphase ensemble as it has been demonstrated that the individual fluids occupy certain positions in the pore space, regardless of the actual values of the respective interfacial properties.

Keywords: Spatial distribution of fluids; Confined systems; USANS; Simulated annealing; Digital reconstruction

A metal-ion-assisted assembly approach to synthesize disulfide-bridged periodical mesoporous organosilicas with high sulfide contents and efficient adsorption by Na Hao; Lu Han; Yunxia Yang; Huanting Wang; Paul A. Webley; Dongyuan Zhao (pp. 5334-5342).

Well-ordered two-dimensional (2D) hexagonal periodic mesoporous organosilicas (PMOs) with a high content of disulfide groups have been prepared by a simple metal-ions-assisted amphiphilic surfactant templating process under a strong acidic condition. Long-chain organic bridge silane, bis(triethoxysilylpropyl)disulfide (BTSPDS) was used as a precursor which can be co-condensed with tetraethoxysilane (TEOS) to assemble with the triblock copolymer Pluronic P123 template and to construct the mesostructured organic–inorganic frameworks. The content of disulfide functional groups is up to 20% (BTSPDS molar content in the initial silane mixture) incorporated into the framework. The obtained ordered mesoporous DS-PMO materials have relatively high BET surface area (∼580m²/g), large uniform pore size (up to 6.3nm) and thick pore walls (thickness up to 7.1nm), because of the long-chain disulfide bridges. The metal ions such as Zn²⁺ formed the four-coordination complex with two sulfides of BTSPDS and ethylene oxide moieties of P123 template, which could enhance the interaction between the “soft” long disulfide groups and P123 template, thus improving the mesostructural regularity correspondingly. The disulfide-bridged PMO materials exhibit excellent hydrothermal stability in boiling water for 5 days, probably due to the thick pore walls. SEM images show that after the hydrothermal treatment, the morphology of the ordered disulfide-bridged PMO materials is retained, as that of the wheat-like SBA-15. Excellent adsorption efficiency (∼716mg/g) for Hg²⁺ ions is observed, suggesting a potential application in removal of heavy metal ions in wastewater.

Keywords: Periodical mesoporous organosilicas; Synthesis; Mesoporous materials; Co-condensation; Self-assembly; Adsorption

An alternative method to remove PEO–PPO–PEO template in organic–inorganic mesoporous nanocomposites by sulfuric acid extraction by Xin Zhuang; Xufang Qian; Jiahui Lv; Ying Wan (pp. 5343-5348).

Sulfuric acid is used as an extraction agent to remove PEO–PPO–PEO templates in the organic–inorganic mesoporous nanocomposites from the triconstituent co-assembly which includes the low-polymerized phenolic resins, TEOS and triblock copolymer F127. The XRD and TEM results show well ordered mesostructure after extraction with sulfuric acid. As followed from the N₂ sorption isotherms the extracted composites possess high surface areas (332–367m²/g), large pore volumes (0.66–0.78cm³/g), and large pore sizes (about 10.7nm). The FT-IR analysis reveals almost complete elimination of triblock copolymer F127, and the maintenance of organic groups. This method shows potentials in removing templates from nanocomposites containing functional moieties.

Keywords: Organic–inorganic composites; Extraction; Sulfuric acid; Mesopore

Optical, structural and adsorption properties of zinc peroxide/hydrogel nanohybrid films by Dániel Sebők; László Janovák; Imre Dékány (pp. 5349-5354).

Hybrid nanofilms from zinc-peroxide/poly(acrylamide) (ZnO₂/PAAm) and zinc-peroxide/poly(N-isopropyl-acrylamide) (ZnO₂/PNIPAAm) were prepared using the photopolymerization procedure. The thin layers were prepared by the combination of the Layer-by-Layer (LbL) self-assembly method and photopolymerization using UV light in every step of the procedure. The hybrid multilayer films consisting of layers of zinc peroxide nanoparticles and hydrogel alternating in a sandwich-like fashion with thicknesses of 65–246nm. The chemical structures of the hybrid films were investigated by FTIR spectroscopy, their morphology was studied by atomic force microscopy (AFM). The build up of the films was studied by measuring the optical reflection spectrum, and we have calculated the refractive index and layer thickness of the hybrid layers using simulating software. The adsorption properties of the ZnO₂/hydrogel nanohybrid composite networks were investigated by measuring water and ethanol vapour adsorption by a quartz crystal microbalance (QCM). It was established that on partially hydrophobic ZnO₂/PNIPAAm hybrids the adsorbed amounts were lower, against the hydrophilic ZnO₂/PAAm film the vapour amount was higher. These results correspond to those of the bulk gel swelling results.

Keywords: ZnO; ₂; nanoparticles; ZnO; ₂; nanohybrid films; Hydrogel; Adsorption; Self assembly; Photopolymerization

Analysis of structure and properties of active carbons and their copolymeric precursors by M. Sobiesiak; B. Gawdzik; A.M. Puziy; O.I. Poddubnaya (pp. 5355-5360).

The relations between chemical structures of BM-DVB copolymers obtained with various monomer molar ratios and their carbonization products were studied. Three porous copolymers 1:4, 1:1, and 4:1 of BM to DVB were the starting materials for preparation of active carbons. Two activation agents were employed: air and phosphoric acid. The carbonization process was performed in the same way in these two cases. To characterize the obtained materials FTIR spectroscopy, thermal and elemental analyses were applied. Porous structure parameters were obtained by means of nitrogen sorption. The results proved that differences in the molar ratio of monomers used in the syntheses of polymeric precursor play a key role for structure and properties of copolymers but have rather small influence on properties of the obtained carbons. Preliminary treatment is more effective during the activation process. The carbons obtained by activation with phosphoric acid are microporous and have well developed porous structures. The air activated carbons are mesoporous with specific surface areas similar to those of polymeric precursors.

Keywords: Active carbons; Porous polymers; Adsorbents; Porosity

Surface heterogeneity of polysiloxane xerogels functionalized by 3-aminopropyl groups by Yu.L. Zub; N.V. Stolyarchuk; M. Barczak; A. Dąbrowski (pp. 5361-5364).

DRIFT spectra of xerogels synthesized by co-condensation of tetraethoxysilane (or 1,2-bis(triethoxysilyl)ethane) and 3-aminopropyltriethoxysilane have been measured using termoevacuation in the temperature range 50–350°C. The disappearance of bands related to the vibrations of water molecule with temperature growth and shifts of absorption band related to the deformation vibrations of amino groups to the high-frequency region have been observed. The formation of a new band in the range of 3650–3660cm⁻¹ has been attributed to stretching vibrations of silanol groups. The simplest change of surface layer composition in the amino-containing xerogels by water removal results in transformation of one type of hydrogen bond to another. The first type is associated with forming of cyclical structure with participation of 3-aminopropyl and silanol groups and water molecule, [≡Si(CH₂)₃H₂N···HO(H)···HOSi≡], the other type is associated with the interaction of amino groups between each other.

Keywords: Sol–gel method; Polysiloxanes; Xerogels; Amino groups; Surface heterogeneity; DRIFT

Molecular simulation of C₆₀ adsorption onto a TiO₂ rutile (110) surface by A.J. Palace Carvalho; J.P. Prates Ramalho (pp. 5365-5369).

A Monte Carlo molecular simulation study is presented on the adsorption and growth of C₆₀ films on the surface of the (110) face of rutile. Simulations are performed for a temperature of 600K using atomistic models both for the fullerene molecules and the TiO₂ surface. It is found in this work that C₆₀ is adsorbed preferably in an ordered arrangement along the surface depressions over the exposed undercoordinated Ti cations. At low densities adsorption occurs preferably at alternate rows, with locations in consecutive rows being occupied appreciably only at higher C₆₀ densities. At low densities, the fullerene molecules tend to aggregate into islands in the surface plane. Additional layers of C₆₀ form only as the density increases, and do so before a monolayer is completed in all consecutive rows. Full monolayer capacity obtained at the highest densities is about 0.9C₆₀ molecules per nm², but this is only achieved by completing the packing of molecules in interstices at a slightly upper level. The fraction of the molecules that lie closest to the surface only amounts to 0.6molecules per nm².

Keywords: Fullerenes; Thin film; Deposition; Monolayer structure; Self-assembly; Clusters

Functionalized SBA-15 organosilicas as sorbents of zinc(II) ions by M. Barczak; E. Skwarek; W. Janusz; A. Dąbrowski; S. Pikus (pp. 5370-5375).

SBA-15 nanoporous silicas functionalized with amine-, thiol-, vinyl-, phenyl- and cyano surface groups were synthesized by using the amphiphilic block copolymer P123 as the structure-directing agent. The obtained materials have a well-developed porous structure – the values of specific surface area are in the range 800–950m²/g and the sizes of cylindrical mesopores are in the range 7.4–8.6nm. It was established that the size of the mesopores strongly depends even on small amounts of co-monomers co-condensing with TEOS. Adsorption of Zn(II) ions at the SBA-15/NaCl interface was investigated by means of the radioactive isotope tracer technique over the pH range of 3–11. Surface charge density, adsorption density, pH_50% and ΔpH_10–90% parameters for different concentrations of the carrying electrolyte were evaluated and discussed.

Keywords: Adsorption; Porosity; SBA-15; XRD; Adsorption of Zn(II) ions

Monte Carlo model of CO adsorption on supported Pt nanoparticle by A.V. Myshlyavtsev; P.V. Stishenko (pp. 5376-5380).

For molecular simulations with thousands of atoms it is desirable to use a lattice gas model because it is fast and easy-to-use for computations. Unfortunately, simulation of adsorption on heterogeneous surfaces within this model is rather complicated due to a large variety of available adsorption site types. We propose the combined model with lattice representation of adsorbent atoms and arbitrary location of adsorbate atoms. Using this model simulation of CO adsorption on supported Pt nanoparticles has been performed. With the proposed approach the above-mentioned difficulties were successfully overcome.

Keywords: Adsorption; Monte Carlo simulation; Pt nanoparticle; Carbon monoxide

Mapping charge-mosaic surfaces in electrolyte solutions using surface charge microscopy by Jaroslaw Drelich; Xihui Yin (pp. 5381-5387).

A significant limitation of electrokinetic measurements is that only an average value of the zeta potential/streaming potential is measured—regardless of whether the surface charge distribution is homogeneous or otherwise. However, in real-world situations, nearly all solids (and liquids) of technological significance exhibit surface heterogeneities. To detect heterogeneities in surface charge, analytical tools which provide accurate and spatially resolved information about material surface potential—particularly at microscopic and sub-microscopic resolutions—are needed.A novel AFM-based technique for mapping surface charge domains on heterogeneous surfaces, which we call Surface Charge Microscopy ( SCM), was recently introduced by our research team. It relies on recording colloidal force curves over multiple locations on the substrate surface using small probes. The surface charge characteristics of the heterogeneous substrate are determined from the recorded colloidal force curves, allowing for the surface charge variation to be mapped. In this communication, we briefly review the SCM technique. Examples of results of measurements of the surface interaction forces that were recorded between a silicon nitride AFM cantilever and a multi-phase volcanic rock and heterogeneous surface of bitumen are also given.

Keywords: Atomic force microscopy; Colloidal probe; Surface charge density; Surface charge microscopy; Surface potential

Deposition of latex particles encapsulated in polyelectrolyte shells at heterogeneous metal surfaces modified by multilayer films by Lilianna Szyk-Warszynska; Anna Trybala; Piotr Warszynski (pp. 5388-5394).

We used an oblique impinging jet (OIJ) cell to determine the initial deposition rate for the microcapsules deposited on the heterogeneous metal surfaces bare or modified by polyelectrolyte (PE) films. The dependence of reduced particle flux on the Reynolds number of the flow in the OIJ cell was determined by direct counting of particles deposited on the studied surfaces. We used fluorescently labelled latex particles and microcapsules built on these fluorescent cores and the use of fluorescent microscope allowed us to observe “in situ” the deposition processes of particles on rough, highly reflective surfaces. We demonstrated that modification of metallic surfaces of various materials and heterogeneity by the multilayer PE films result in the formation of uniformly charged film of nanometers thickness. The formation of such a film leads to the increase of deposition efficiency and its initial rate is governed by the charge of the film covered surface and the outermost layer of the capsule shell being in agreement with the prediction of the convective-diffusion theory.

Keywords: Deposition; Microcapsules; Heterogeneous surfaces; Metal surfaces polyelectrolyte; Layer-by-layer; Adsorption

Ordered mesoporous solids as model substances for liquid adsorption by G. Kalies; R. Rockmann; D. Tuma; J. Gapke (pp. 5395-5398).

Two different ordered mesoporous solids, a hexagonal SBA-15 silica sample and its inverse CMK-3 carbon structure were applied in liquid-phase adsorption. By means of the analysis of experimental data of a binary liquid model mixture with one polar and one non-polar component, the general way is outlined how to obtain essential and trustworthy solid information from liquid-phase adsorption.

Keywords: Adsorption excess isotherm; Ordered mesoporous solid; Binary liquid mixture; Thermodynamics; Solid heterogeneity

Evaluating the surface density and heterogeneity of a dithiobis (succinimidylpropionate) self-assembled monolayer on gold and its coupling with DNA embedded within a matrix by Walter E. Rudzinski; Kevin Francis (pp. 5399-5405).

The homogeneity of a self-assembled monolayer (SAM) on a surface is an important parameter which affects the ability of a SAM to fulfill its intended function. As an example, SAMs formed from octanethiols can form an impermeable surface, while SAMs based on a bifunctional coupling reagent can form a surface with uniform reactivity. Exposure of gold nanoparticles or gold surfaces to solutions of dithiobis (succinimidylpropionate) (DSP) gives rise to a surface which can react with DNA. Atomic force microscopy, UV–vis and gel electrophoresis experiments indicate that a self-assembled monolayer of DSP on gold nanoparticles can attenuate aggregation, inhibit the “lying down” of covalently-bound single-stranded (ss) DNA and promote more efficient hybridization. The determination of the point of aggregation after reacting DSP with colloidal gold yields 2.86×10⁻¹⁰mol/cm² or 42% of the value determined from molecular modeling. Cyclic voltammetry experiments validate that DSP on a gold quartz crystal (6.3×10⁻¹⁰mol/cm²) forms a fairly uniform SAM that is within 94% of maximum coverage when compared with results obtained from molecular modeling (6.67×10⁻¹⁰mol/cm²). Surface plasmon resonance experiments indicate that the reaction of a DSP coated gold surface with (ss) DNA yields 2.4×10⁻¹²mol/cm² or reaction with about 1% of the available surface area. Subsequent reactions of the DSP surface with the filler, n-boc-1,4-phenylene diamine ( n-boc), yield a total surface coverage of 1.8×10⁻¹¹mol/cm². The surrounded (ss) DNA yields a surface with 97% hybridization efficiency toward the complement.

Keywords: Dithiobis (succinimidylpropionate); Self-assembled monolayer; DNA; Gold nanoparticles; Gold; Surface plasmon resonance

Adsorption of Al₁₃–Keggin clusters to sapphire c-plane single crystals: Kinetic observations by streaming current measurements by J. Lützenkirchen; T. Kupcik; M. Fuss; C. Walther; A. Sarpola; O. Sundman (pp. 5406-5411).

We have carried out streaming current measurements of sapphire c-plane single crystals in contact with the solutions containing the Al₁₃–ɛ-Keggin ions at different pH values. We followed the evolution of the zeta-potential as a function of time and pH.The Keggin ions were synthesised and characterised by ESI-MS in two different laboratories, and the results showed that nearly 100% of Al was in the form of Al₁₃ cluster.The streaming current measurements were carried out to investigate whether Al₁₃ clusters would (i) be adsorbed to the surface and (ii) remain stable. Close to the isoelectric point of the sapphire c-plane (around pH 4) it was found that the Al₁₃ ions were adsorbed and stable in the systems for an extended period. After some time the conductivity of the solution strongly increased and the zeta-potential declined, indicating that the clusters were destroyed (certainly in solution, as indicated by the conductivity reading, but potentially also at the surface). ESI-MS measurements at various dilution factors or decreased pH also showed disintegration of the clusters resulting in a multitude of smaller Al species, in agreement with the conductivity measurements during the streaming current measurements. Additions at higher pH showed clear adsorption of the clusters but resulted in stability over the complete observation period as inferred from the conductivity measurements.

Keywords: Sapphire c-plane; Single crystals; Zeta-potential; Speciation; Al; ₁₃; Isoelectric point; ESI-MS

The effect of electrolytes on the surface potential at the rutile/aqueous interface by Tajana Preočanin; Atiđa Selmani; Darko Mazur; Nikola Kallay (pp. 5412-5415).

The method for evaluation of surface potential from the electrode potential of single crystal electrodes is refined. The effect of NaCl and LiCl concentrations on the dependency of the surface potential of TiO₂ on pH was examined. The point of zero potential was shifted to lower pH values in the presence of NaCl and to higher pH values in the presence of LiCl. The interpretation of the data based on the Surface Complexation Model suggested that at 001 crystal plane of rutile, sodium ions as counterions have more pronounced affinity for association with negatively charged surface groups with respect to the lithium ions.

Keywords: Surface potential; Point of zero potential; Titania; Rutile; Counterion association

Characterization of uranium(VI) sorption by organobentonite by Marek Majdan; Stanisław Pikus; Agnieszka Gajowiak; Agnieszka Gładysz-Płaska; Halina Krzyżanowska; Jerzy Żuk; Monika Bujacka (pp. 5416-5421).

The U(VI) sorption on the bentonite modified by hexadecyltrimethylammonium bromide (HDTMA) was studied in the concentration range: 0.0001–0.001mol/dm³ in the aqueous phase and in the pH range: 3–10. The experiments concerning the pH influence on the molar absorption coefficient c_b of U(VI) in the bentonite phase showed that the species: UO₂²⁺, UO₂(OH)⁺, UO₂(OH)₂ UO₂(OH)₃⁻, UO₂(OH)₄²⁻, (UO₂)₃(OH)₅⁺, (UO₂)₃(OH)₇⁻, present in the aqueous phase, are responsible for uranium sorption. Their sorption parameters K were determined and it is evident that for higher concentrations of HDTMA⁺ cations in the bentonite phase, i.e. for b96–b157 bentonite, the presence of anionic species: UO₂(OH)₃⁻, UO₂(OH)₄²⁻, and (UO₂)₃(OH)₇⁻ in the aqueous phase results in the increase of U(VI) molar absorption coefficient c_b in the sorbent phase.

Keywords: Uranium; Sorption; Organobentonite; Hexadecyltrimethylammonium bromide

Adsorption and solid phase extraction of 8-hydroxyquinoline from aqueous solutions by using natural bentonite by Bilge Erdem; Adnan Özcan; A. Safa Özcan (pp. 5422-5427).

The nitrogen-heterocyclic compound 8-hydroxyquinoline (8HQ) is one of the components of coal tar and has a wide variety of uses in industry. Because of its toxicity for aquatic organisms and harmful effects for human health, the removal of 8HQ from aqueous solutions by adsorption onto natural bentonite was investigated in the present work. The experimental results show that the optimum pH value of 2.5 is favourable for the 8HQ adsorption. The experimental data were fitted well with the pseudo-second-order kinetic and Langmuir adsorption isotherm models at all studied temperatures. The maximum adsorption capacity obtained from the Langmuir isotherm model at 20°C was 120.6mgg⁻¹. The calculated thermodynamic results such as Δ G° (−24.3kJmol⁻¹) and Δ H° (−9.56kJmol⁻¹) indicate that the adsorption process is spontaneous and exothermic in nature. Solid phase extraction of 8HQ was also performed. The X-ray diffractometry (XRD), Fourier Transform Infrared (FTIR) and thermogravimetric (TG) analyses were carried out in order to confirm the 8HQ adsorption onto bentonite. According to the obtained results, natural bentonite can be a reusable and effective adsorbent for the removal of 8HQ.

Keywords: Natural bentonite; 8-Hydroxyquinoline; Adsorption; Kinetics; Isotherm; Thermodynamics

Analysis of adsorption properties of N719 dye molecules on nanoporous TiO₂ surface for dye-sensitized solar cell by Kyung-Jun Hwang; Wang-Geun Shim; Sung-Hoon Jung; Seung-Joon Yoo; Jae-Wook Lee (pp. 5428-5433).

Ordered nanoporous TiO₂ materials (MK-TiO₂, MS-TiO₂, and MU-TiO₂) were synthesized for the dye-sensitized solar cell (DSSC) by using different silica templates such as KIT-6, SBA-15, and MSU-H. To prepare a photoelectrode in DSSC, cis-bis(isothiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)-ruthenium(II)bis-tetrabutylammonium dye (N719) was adsorbed onto the synthesized nanoporous TiO₂ materials. The samples were characterized by XRD, TEM, FE-SEM, AFM, and N₂ adsorption analyses. The photovoltaic performance of DSSC was evaluated from the overall conversion efficiency, fill factor, open-circuit voltage, and short-circuit current from the I– V curves measured. It was found that the photoelectric performance is highly dependent on the adsorption properties of N719 dye molecules on the nanoporous TiO₂ replicas (MK-TiO₂, MS-TiO₂, and MU-TiO₂) synthesized from different silica templates.

Keywords: Adsorption; Nanoporous TiO; ₂; N719; Dye-sensitized solar cells; SBA-15; MSU-H; KIT-6

Removal of recalcitrant pollutants from wastewater by S. Pasieczna-Patkowska; B. Czech; J. Ryczkowski; J. Patkowski (pp. 5434-5438).

Triton X-100 was oxidized in aqueous solutions with the presence of O₂ using photocatalysis and H₂O₂ addition alone or coupled. New supported TiO₂/Al₂O₃ catalysts modified with vanadium and cobalt were used. Catalysts were prepared using the classical impregnation method (CIM) and the double impregnation method (DIM). The effect of the physico-chemical properties of the catalysts on its activity were studied. The research on the interactions between the metal precursor and the titania–alumina surface by means of FT-IR/PAS (Fourier transform infrared photoacoustic spectroscopy) were also conducted.

Keywords: Photocatalysis; TiO; ₂; /Al; ₂; O; ₃; Wastewater treatment; Advanced oxidation processes; FT-IR/PAS

Adsorption behavior of a textile dye of Reactive Blue 19 from aqueous solutions onto modified bentonite by Özer Gök; A. Safa Özcan; Adnan Özcan (pp. 5439-5443).

The aim of this study is to evaluate adsorption kinetics, isotherms and thermodynamic parameters of Reactive Blue 19 (RB19) onto modified bentonite from aqueous solutions. The effects of pH, contact time, initial dye concentration and temperature were investigated in the experimentally. Natural bentonite was modified by using 1,6-diamino hexane (DAH) as a modifying agent. The characterization of modified bentonite (DAH-bentonite) was accomplished by using FTIR, TGA, BET and elemental analysis techniques. The optimum pH value for the adsorption experiments was found to be 1.5 and all the experiments were carried out at this pH value. The pseudo-second-order kinetic model agrees very well with the experimental results. Equilibrium data were also fitted well to the Langmuir isotherm model in the studied concentration range of RB19 at 20°C. The results indicate that DAH-modified bentonite is a suitable adsorbent for the adsorption of textile dyes.

Keywords: Adsorption; Clay; Modified bentonite; Dye; RB19; Kinetics; Isotherms

Co-adsorption of surfactants and propyl gallate on the hydrophilic oxide surfaces by Mateusz Drach; Jerzy Jabłoński; Jolanta Narkiewicz-Michałek; Marta Szymula (pp. 5444-5448).

Propyl gallate (PG) adsolubilisation in the cationic, anionic and nonionic surfactant micelles formed in the bulk solution and at the silica/solution interface has been investigated. It was found that in the absence of surfactant, propyl gallate does not adsorb on the silica surface from aqueous solution. However, in the presence of hexyltrimethylammonium bromide (CTAB), its uptake by silica significantly increases. Alumina is quite an effective adsorbent for SDS and propyl gallate and does not adsorb nonionic TX-100. The addition of PG promotes adsorption of SDS and TX-100.

Keywords: Adsolubilisation; Surfactant adsorption; Aggregation; Antioxidant

Adsorption of biodegradable chelating compounds on inorganic oxides by A. Dębczak; J. Ryczkowski; J. Patkowski (pp. 5449-5452).

The Fourier transform infrared photoacoustic spectroscopy (FT-IR/PAS) method to characterize the interactions between selected aminopolycarboxylic acids and inorganic oxides surfaces is reviewed. In this work, the adsorption of four aminopolycarboxylates (biodegradable and with augmented biodegradability; all in the form of sodium salts), viz. ethylenediaminedisuccinic (EDDS), diethylenetriaminepentaacetic (DTPA), N-(hydroxyethyl)ethylenediaminetriacetic (HEDTA) and methylglycinediacetic (MGDA) acids on: zirconia, titania and alumina was carried out. The obtained results differ depending on the kind of aminopolycarboxylic acid used and the type of oxide support adsorbent characterized by its pH_PZC value.

Keywords: Aminopolycarboxylates; Inorganic oxides; FT-IR/PAS

Regeneration of thiol-functionalized mesostructured silica adsorbents of mercury by Amaya Arencibia; José Aguado; Jesús M. Arsuaga (pp. 5453-5457).

The regeneration of thiol-functionalized SBA-15 adsorbents of mercury is presented in this article. The influence of temperature and pH on the adsorption process was studied. The effect due to the presence of complexing agents in aqueous solution on the desorption step was also evaluated. Hg(II) maximum adsorption capacities at different temperatures ranging from 20°C to 60°C were obtained and it was found that temperature does not affect the adsorption process. Mercury adsorption capacity was also determined in the presence of HNO₃ and HCl up to 3M concentration. The comparison of the results showed that whereas hydrochloric acid exhibits an appreciable capacity to regenerate the thiol-functionalized SBA-15 adsorbent, the nitric acid results inefficient. The difference was attributed to the mercury complexing ability of chloride anion. Four complexing compounds, KBr, KSCN, (NH₂)₂CS, and HBr were tested for desorbing mercury in regeneration experiments. All agents were able to remove significant amounts of adsorbed mercury, being hydrobromic acid the complexing compound that yields the best results.

Keywords: Mesostructured silica; Thiol functionalization; Mercury removal; Adsorbent regeneration

Removal of fluoride in aqueous solution by adsorption on acid activated water treatment sludge by Soydoa Vinitnantharat; Sriwilai Kositchaiyong; Siriluk Chiarakorn (pp. 5458-5462).

This paper reports the use of a pellet of adsorbent made from water treatment sludge (S) and acid activated water treatment sludge (SH) for removal of fluoride in the batch equilibration technique. The influence of pH, adsorbent dosage, temperature and effect of other ions were employed to find out the feasibility of acid activated adsorbent to remove fluoride to the permissible concentration of 0.7mg/L. The results from the adsorption isotherm followed both Langmuir and Freundlich models and the highest fluoride removal was found for adsorbent activated with acetic acid at 2.0mol/L. The optimum adsorbent dosage was found at 40g/L, 0.01mol/L acid activated adsorbent which was able to adsorb fluoride from 10 down to 0.11mg/L. The adsorption capacity was decreased when the temperature increased. This revealed that the adsorption of fluoride on SH was exothermic. In the presence of nitrate and carbonate ions in the aqueous solution, fluoride removal efficiency of SH decreased from 94.4% to 86.6% and 90.8%, respectively. However, there is no significant effect in the presence of sulfate and chloride ions.

Keywords: Defluorination; Adsorption; Water treatment sludge; Surface modification

Changes in wetting and energetic properties of glass caused by deposition of different lipid layers by Monika Gołąbek (Mirosław); Lucyna Hołysz (pp. 5463-5469).

An investigation of wetting and energetic properties of different lipid layers deposited on the glass surface was carried out by contact angles measurements and determination of the apparent surface free energy. The topography of the lipid layers was also determined with the help of atomic force microscopy (AFM). Two synthetic phospholipids were chosen for these studies, having the same phosphatidylcholine headgroup bound to the apolar part composed either by two saturated chains (1,2-dipalmitoyl- sn-glycero-3-phospshocholine – DPPC) or two unsaturated chains (1,2-dioleoyl- sn-glycero-3-phosphocholine – DOPC) and one lipid (1,2,3-trihexadecanoyl- sn-glycerol – tripalmitoylglycerol – TPG). The lipid layers, from the 1st to the 5th statistical monolayer, were deposited on the glass surface from chloroform solutions by spreading.The apparent surface free energy of the deposited layers was determined by contact angles measurements (advancing and receding) for three probe liquids (diiodomethane, water, and formamide), and then two concepts of interfacial interactions were applied. In the contact angle hysteresis approach (CAH) the apparent total surface free energy was calculated from the advancing and receding contact angles and surface tension of probe liquids. In the Lifshitz–van der Waals/acid–base approach (LWAB) the total surface free energy was calculated from the determined components of the energy, which were obtained from the advancing contact angles of the probe liquids only. Comparison of the results obtained by two approaches provided more information about the changes in the hydrophobicity/hydrophilicity of the layers depending on the number of monolayers and kind of the lipid deposited on the glass surface.It was found that the most visible changes in the surface free energy took place for the first two statistical monolayers irrespectively of the kind of the lipid used. Additionally, in all cases periodic oscillations from layer-to-layer in the lipid surface free energy were observed. The changes in the surface free energy correlated with those in the topography and roughness of lipid layers.

Keywords: Wetting; Contact angle; Surface free energy; Lipids

Adsorption of paracresol in silicalite-1 and pure silica faujasite. A comparison study using molecular simulation by L. Narasimhan; Pascal Boulet; Bogdan Kuchta; Christelle Vagner; Oliver Schäf; Renaud Denoyel (pp. 5470-5474).

This paper presents the results on the Grand-Canonical Monte Carlo simulations of the adsorption of the paracresol uremic toxin and water into the silicalite-1 and pure silica faujasite zeolites. The co-adsorption of water and paracresol seems to proceed along a cooperation effect between the toxin and the solvent. A model of adsorption that accounts for the effect of the solvent has been elaborated and verified using experimental isotherms. The model is based on the Langmuir isotherm in which an apparent adsorption enthalpy is used that changes with the concentration of the solute. The new expression for the isotherm reproduces the experimental isotherm with good accuracy and physical interpretation is given to justify the model.

Keywords: Adsorption in porous materials; Co-adsorption; Monte Carlo simulations; Paracresol; Uremic toxins; Zeolites

Effect of different solid matrixes on surface free energy of EGDMA and TRIM polymers by Konrad Terpilowski; Emil Chibowski (pp. 5475-5481).

Advancing and receding contact angles of water, formamide, glycerol and diiodometane were measured on the two polymers; EGDMA (dimethacrylate of ethylene glycol) and TRIM (trimethacrylate-1,1,1-trihydroksymethylopropane) which were polymerized next to glass, silanized glass, stainless steel, mica and silicon surfaces as the matrices. Then from the contact angle hystereses (CAH) and van Oss, Good, Chaudhury (LWAB) approaches the apparent surface free energies were evaluated. The measured contact angles not only depend solely on the polymer chemical structure but also, to some extent, on the solid matrix next to whose surface the sample has polymerized. Surface free energy of the polymer samples calculated from the LWAB approach shows that they interact mainly by dispersive forces. The apparent surface free energy of the polymers calculated from the diiodomethane contact angles hysteresis is practically the same irrespective of the kind of the matrix used. Therefore it can be concluded that the observed weak polar interactions in the surface free energy of the samples depend on the polymer surface preparation. The AFM images show that the obtained surfaces are of different roughness. The RMS values of roughness range between 3.7–90.2nm for EDGMA, and 5.3–124.5nm for TRIM. However, as reported in literature, rather protrusions bigger than 1μm may significantly affect the contact angles, especially the receding ones.

Keywords: EGDMA and TRIM polymers; Contact angles; Surface free energy; Effect of matrixes

Water vapour sorption on hydrophilic and hydrophobic nanoporous materials by Dirk Enke; Michael Rückriem; Andreas Schreiber; Jürgen Adolphs (pp. 5482-5485).

The aim of this study is to compare water vapour sorption isotherms on various mesoporous materials in their pristine state and after silanisation. Commonly the pristine state is regarded as hydrophilic and the silanised one as hydrophobic. Water vapour sorption experiments are discussed for a highly ordered nanoporous aluminium oxide with straight cylindrical channels of ca. 25nm diameter and for various controlled porous glasses (CPGs) with disordered pores in the range of 13nm diameter. The water sorption isotherms exhibit in both cases a hysteresis over the entire humidity range. At higher humidities the pristine materials show capillary condensation whereas for the silanised samples this phase transition does not occur or even a loss of water is recorded as for the silanised Al₂O₃. Surprisingly, for the silanised Al₂O higher water uptake is observed in the low humidity region. Application of the excess surface work (ESW) method delivers a reduced structural component in the long range interaction of the water molecules with a hydrophobic surface. Inverse gas chromatography studies of the silanised CPGs result in an increased short range dispersive part of the surface energy with the increasing degree of silanisation.

Keywords: PACS; 68.43.−h; 82.70.UvHydrophilic; Hydrophobic; Nanoporous alumina; Porous glasses; Water adsorption; Excess surface work; Sorption model

Simultaneous adsorption of dyes and heavy metals from multicomponent solutions using fly ash by Maria Visa; Cristina Bogatu; Anca Duta (pp. 5486-5491).

In wastewaters originating from dye industry there are amounts of dyes (very common methyl orange, methylene blue—MB) and heavy metals (cadmium, copper, nickel mainly from the organo-metallic dyes). They tend to adsorb in a competitive process and modify the substrate. Advanced removal is usually proposed via adsorption and the use of modified fly ash as a substrate is sustainable solution. The main constituents of fly ash (silica, alumina, iron oxide and un-burned carbon), are the priority compounds which favour the heavy metal adsorption and are active sites in dyes’ adsorption processes. The paper studies the effect of MB adsorbed on the fly ash surface on the removal efficiency of cadmium, copper and nickel ionic species from complex, multi-cationic dye solutions. The adsorption efficiency and kinetics are evaluated from the complex, multicomponent systems and possible influences are discussed. High efficiencies are obtained at low heavy metal concentrations (as it is the real case for the dyes industry) whereas at medium values, competitive processes lower the individual efficiencies of copper, nickel or cadmium from mixtures.

Keywords: Fly ash; Heavy metal removal; Dyes; Wastewater treatment

Development of new composite biosorbents from olive pomace wastes by Francesca Pagnanelli; Carolina Cruz Viggi; Luigi Toro (pp. 5492-5497).

In this study olive pomace was used as a source of binding substances for the development of composite biosorbents to be used in heavy metal removal from aqueous solutions. The aim was to obtain biosorbent material with an increased concentration of binding sites. The effects of two different extraction procedures (one using only methanol and the other one hexane followed by methanol) on the binding properties of olive pomace were tested by potentiometric titrations and batch biosorption tests for copper and cadmium removal. Titration modelling evidenced that both kinds of extractions generated a solid with a reduced amount of protonatable sites. Biosorption tests were organized according to full factorial designs. Analysis of variance denoted that both kinds of extractions determined a statistically significant negative effect on metal biosorption. In the case of cadmium extractions also determined a significant decrease of selectivity with respect to olive pomace.When the acid-base and binding properties of the substances extracted were determined, they were adsorbed onto a synthetic resin (octadecylsilane) and calcium alginate beads. In this way two kinds of composite biosorbents have been obtained both having an increased concentration of binding substances with respect to native olive pomace, also working more efficiently in metal removal.

Keywords: Olive pomace; Biosorption; Potentiometric titration; Modelling; Heavy metals

Heats of interaction of hydrogen with gold and platinum powders and its effect on the subsequent adsorptions of oxygen and noble gases by Aleksander J. Groszek; Erwin Lalik; Jerzy Haber (pp. 5498-5502).

Exposure of pure gold powders to hydrogen flow at 125°C and atmospheric pressure causes heat evolution accompanied by hydrogen adsorption. The exposure takes place in a flow-through microcalorimeter, in which the metal powders are purged by nitrogen flow used as an inert carrier gas. The adsorbed hydrogen is slowly desorbed by nitrogen flow. The heats of hydrogen adsorption and its uptake by the gold powder are greatly increased by its sequential treatments with micromole quantities of oxygen and noble gases, such as helium and argon. This increase does not take place if the gold treatment is confined only to oxygen, or only to pure noble gases. The radically increased hydrogen adsorption by gold is caused by a combination of its treatments with oxygen and the noble gases. Similar results were obtained with pure platinum powder exposed to hydrogen at room temperatures. Gold powder containing adsorbed hydrogen reacts very strongly with molecular oxygen/argon mixtures, generating heats of adsorption several times higher than the heat of formation of water. The heat evolution is very rapid and is not accompanied by the formation of water. These intense interactions are not observed after complete desorption of hydrogen from the gold surfaces.

Keywords: Gold powder; Platinum powder; Hydrogen; Noble gases; Oxygen; Adsorption

Separation of chiral molecules by temperature programmed desorption by Paweł Szabelski (pp. 5503-5507).

The Monte Carlo simulation method was used to model thermal desorption of a pair of enantiomers from a solid surface with a chiral periodic pattern of active sites. The main objective of the study was to determine the optimal number of the active sites and their spatial distribution within the unit cell of the surface to achieve the most efficient separation of the enantiomers. For that purpose we tested the series of chiral patterns which were found previously for the equilibrium adsorption. Temperature programmed desorption spectra were calculated using a square lattice of adsorption sites in which the active sites were distributed spatially according to the candidate patterns. Additionally, influence of relaxation of the adsorbed layer on the relative shift of the TPD peaks of the enantiomers was assessed and the key factors affecting the chiral separation were identified.

Keywords: PACS; 68.43.h; 68.43.De; 68.03.Hj; 68.43.VxChiral molecules; Thermal desorption; Monte Carlo simulation; Enantioseparation

Length dependency of hydrocarbon adsorption on nanostacked MFI zeolite by tracer chromatography by Hailian Jin; Eko Adi Prasetyanto; Nanzhe Jiang; Soon-Moon Oh; Sang-Eon Park (pp. 5508-5512).

The adsorption behaviour of a series of n-alkanes, alkyl aromatics, and alcohols on different morphology TS-1 (Titanium Silicalite-1) zeolites were studied using the tracer chromatographic technique at the temperatures in the 473–573K range. The adsorption studies were performed with nanostacked TS-1 (NSTS-1) and nonstacked TS-1 (TS-1). The NSTS-1 exhibits the stacked morphologies due to dehydration of hydroxyl groups on the external surface of crystallites through the selective absorption of microwave onto Ti species. The Henry constants and adsorption enthalpies have been estimated. The straight channels of the NSTS-1 having long pathway gave different selectivity in the Henry constants of long-chained hydrocarbons due to strong interaction with straight channel in stacked morphology, which gave the larger Henry constant than the TS-1. The Henry constants linearly increase with the increasing carbon number since more interactions are possible for long chains.

Keywords: Tracer chromatography; Henry constant; NSTS-1; TS-1; Microwave; Hydrocarbon adsorption

Mesoporous “core–shell” adsorbents and catalysts with controllable morphology by Marina V. Barmatova; Irina D. Ivanchikova; Elena I. El’kina; Alexander N. Shmakov; Maxim S. Mel’gunov; Vladimir B. Fenelonov (pp. 5513-5519).

A simple geometrical model is applied to predict the thickness of mesoporous shells over monodisperse spherical particles. As an example, mesoporous Ti-silicate nearly monodisperse particles with the “core–shell” structure, synthesized via the one-pot procedure are considered. The unique features of the materials are orientation of mesopores perpendicularly to the surface of non-porous cores and uniformity of mesoporous shells structure and thickness. This allows considering these materials as interesting catalysts for partial oxidation of bulk organic molecules with hydrogen peroxide.

Keywords: Mesoporous; Ti-MMM-2; Ti-MCM-41; Ti-SCMS; Core-Shell; Structure

VPO catalysts synthesized on substrates with modified activated carbons by Jadwiga Skubiszewska-Zięba (pp. 5520-5527).

VPO catalysts were prepared on oxidized and unoxidized activated carbons differing in initial porous structure. Carbons were oxidized under relatively soft (30% H₂O₂, 200°C) and hard (50% H₂O₂, 350°C) conditions. Carbon modification was carried out hydrothermally in a traditional autoclave (HTT) or a microwave reactor (MWT). The synthesis was also carried out under hydrothermal (HTS or MWS) conditions. V₂O₅ and NH₄VO₃ were used as precursors. The samples are characterized by diversified porous structure at S_BET=732–1617m²/g and V_por=0.44–0.90cm³/g, as well as various degree of VPO crystallinity. Possibility of preparation of the VPO catalysts under ecologically appropriate conditions, i.e. in aqueous solutions, was shown.

Keywords: PACS; 61.43.Gt; 61.46.Df; 61.46.Hk; 61.10.Nz; 68.35.−p; 74.62.BfActivated carbon; Porous structure; Hydrothermal treatment; VPO catalyst; Crystalline structure

Adsorption and desorption characteristics of barium oxide at high temperature by Jong-Ho Park; Young-Sun Cho; Kwang-Bok Yi; Sang-Sup Han; Soon-Haeng Cho (pp. 5528-5532).

Oxygen-selective adsorbents were prepared by two different methods, hydrothermal and sol–gel methods. The adsorption and desorption characteristics of these adsorbents were compared in terms of stability and sorption capacity. The sorbents prepared by the sol–gel method showed better cyclic stability and higher adsorption capacity than that prepared by the hydrothermal method because the sol–gel method entrapped well the barium peroxide.Relaxation time for adsorption ranged from 4 to 9min depending on the preparation methods and that for desorption was 6min regardless of the preparation methods. Breakthrough experiment with the sorbent prepared by the sol–gel method was performed. The adsorption breakthrough curves at 600°C showed two plateau regions. One was at about 3.5%, and the other was 20%. The first plateau region is related to the sharp transition point of the oxygen adsorption isotherm. Though the relaxation time for adsorption was 6min, the time required from the end of the first plateau to the beginning of the second plateau was just 2min. During the desorption, a plateau region at 3.5% of oxygen concentration was observed regardless of the desorption flow rate.

Keywords: Barium oxide; Oxygen adsorbent; Sol–gel method; Sorption characteristic; High temperature

The n-butyl amine TPD measurement of Brönsted acidity for solid catalysts by simultaneous TG/DTG–DTA by V. Sasca; Livia Avram; Orsina Verdes; A. Popa (pp. 5533-5538).

The method for Brönsted acidity measurement based on TPD of alkyl amines desorption by gas-chromatography or thermogravimetry was adapted for simultaneous TG/DTG–DTA analysis. The acidity measurements were focused on the 12-tungstophosphoric acid (H₃PW₁₂O₄₀) and its salts, especially with Cesium since these posses the highest Brönsted acidity and they are among the most interesting catalysts. The n-butyl amine (NBA) desorption takes place in three steps for Cs_xH3−_xPW₁₂O₄₀, x=0–2, and four steps for the Cs_2.5H_0.5PW₁₂O₄₀. The steps of desorption correspond to the release of NBA molecules in stages, as NBA or butene molecules resulted from the Hofmann elimination reaction and NH₃+H₂O formed by decomposition of ammonium salt. The quantities of desorption products, C₄H₈ and NH₃+H₂O, corresponding to the stages with the maximum desorption rates at 400–420°C, respectively 560–600°C, are in the stoichiometric ratio with the Brönsted acidity.

Keywords: TPD measurement; Brönsted acidity; n-Butyl amine desorption; TG/DTG–DTA analysis; 12-Tungstophosphoric acid; Cs; _x; H; 3−; _x; PW; ₁₂; O; ₄₀; acidity

Thermal treatment of organoclays: Effect on the aqueous sorption of nitrobenzene on n-hexadecyltrimethyl ammonium montmorillonite by Mikhail Borisover; Nadezhda Bukhanovsky; Isaak Lapides; Shmuel Yariv (pp. 5539-5544).

The aim of this work was to examine the effect of thermal treatment on organoclay sorptive properties. Aqueous sorption of nitrobenzene used as a probe compound was studied on Na-montmorillonite and two types of HDTMA-montmorillonite (where HDTMA is n-hexadecyltrimethyl ammonium exchanged by 41 and 90% of the clay cation exchange capacity) heated in air at 150, 250, 360 and 420°C. Mild heating of sorbents (at 150°C) results in a distinct increase of their sorptive efficacy. Treatment of organoclays at higher temperatures (250 and 360°C) results in the significant sorbent changes as revealed by a C loss, decrease of a basal spacing and disappearance of symmetric and asymmetric stretching vibrations of CH₂ but has a little impact on the sorptive efficacy (as compared with organoclays treated at 150°C). Hence, even a significant carbon loss in thermally treated organoclays should not be necessarily linked to the loss of their sorptive potential. Further increase of the treatment temperature results in a decrease of a sorptive efficacy of all sorbents. Mild heating of organoclays in air could be useful for improving their sorptive potential. This improvement is assumed to result from the weakening of water–sorbate competition for sorption sites on a mildly heated sorbent.

Keywords: Organoclays; Thermal treatment; Montmorillonite; Equilibrium isotherms; Sorption enhancement; Charcoal

Infrared photoacoustic spectroscopy in catalysis and surface science by Janusz Ryczkowski (pp. 5545-5550).

The analysis of solid samples can often be a difficult problem for the researchers dealing with infrared (IR) spectroscopy. In conventional absorption spectroscopy the measurement of absorption is transferred to that of the radiation transmitted through the sample. Three methods stand out as being more suitable for studying solid materials. These methods are: diffuse reflectance (DR), photoacoustic spectroscopy (PAS), and Fourier transform (FT) Raman. All three methods require little or no sample preparation, and therefore are ideal for the samples that may change during the preparation as mineral oil mulls or KBr disks. In the case of PAS, the adsorbed radiation is determined directly via its heat and hence the sound produced in the sample. Fourier transform infrared PAS (FT-IR/PAS) is one of the main IR techniques which can be successfully applied in catalysis and surface science research. Recent examples of this spectroscopic technique application will be presented.

Keywords: FT-IR/PAS; Catalysis; Surface science

Nano- and micro-powder of zirconia and ceria-supported cobalt catalysts for the steam reforming of bio-ethanol by Andrzej Machocki; Andrzej Denis; Wieslaw Grzegorczyk; Wojciech Gac (pp. 5551-5558).

The usefulness of nano- and micro-powders of ceria and zirconia as a support of the cobalt-based catalyst as well as additional modification of zirconia-supported cobalt catalysts with cerium for the production of hydrogen in the steam reforming of bio-ethanol (SRE) for fuel cell applications was studied. It was found that mainly different structural features of the nano- and micro-powder of ceria- and zirconia-supported cobalt catalysts are higher cobalt surface area and much smaller average sizes of cobalt crystallites for the catalysts with high-dispersed support. Similarly, the presence of high-dispersed ceria introduced to the zirconia-supported catalysts simultaneously with the deposition of cobalt increases their total and active surface area as well as decreases the size of cobalt crystallites, regardless of the initial dispersion of zirconia support. The results of the temperature-programmed reduction and the temperature-programmed desorption of hydrogen showed that small crystallites of the cobalt phase strongly interact with high-dispersed ceria.Ceria has a great influence on the effects of the SRE. For the nano-powder ceria-supported cobalt catalyst and for the nano-powder zirconia-supported catalysts with the cobalt–ceria active phase the yield of hydrogen formed from one molecule of ethanol supplied to the SRE process was the highest; even at the relatively low temperature of 420°C it is close to 5.5molH₂/molEtOH. At the same time there were achieved: complete conversion of ethanol, very close to that of water and 92%, 81–84%, 5–6% selectivities to hydrogen, carbon dioxide and carbon monoxide, respectively.

Keywords: Hydrogen; Bio-ethanol; Steam reforming; Cobalt-based catalysts; Ceria support; Zirconia support

Relation between adsorption and catalysis in the case of NiO and Co₃O₄ by I. Arvaniti; V. Netos; V. Siokos; E. Metaxa; F. Roubani Kalantzopoulou (pp. 5559-5565).

Reversed flow-inverse gas chromatography is a quick, precise and effective methodology to characterize physicochemical properties of adsorbents. This is extended to the experimental measurement of the adsorption energy distribution function as well as of the differential energy of adsorption due to lateral interactions of molecules adsorbed on two catalysts, namely Co₃O₄ and NiO. Thus, the nature and the strength of the adsorbate–adsorbent and adsorbate–adsorbate interactions are extracted in order to give detailed answers to the questions: (a) where are the molecules on the heterogeneous surface and (b) which is the nature of the surface chemical bonds? Thus, adsorption of 1-butene was found to take place immediately and irreversibly. It holds a deep relation between adsorption and catalysis of 1-butene over these catalysts. As a consequence, the adsorption of 1-butene in the presence of hydrogen leads to isobutane and/or n-butane, depending on the temperature. It can be seen from the adsorption/desorption kinetic constants that the adsorption of 1-butene on Co₃O₄ is one order higher than over NiO. This fact in connection with the bigger activation energy and the lower kinetic coefficients concerning hydrogenation reaction over NiO shows that Co₃O₄ is a better catalyst for this kind of catalysis.

Keywords: Reversed flow-inverse gas chromatography; Inverse gas chromatography; Adsorption/catalysis; Chemisorption/physisorption; Hydrogenation of alkenes; Isomerization of alkanes

Heterogeneous adsorption and catalytic oxidation of benzene, toluene and xylene over spent and chemically regenerated platinum catalyst supported on activated carbon by Wang Geun Shim; Sang Chai Kim (pp. 5566-5571).

The heterogeneous adsorption and catalytic oxidation of benzene, toluene and o-xylene (BTX) over the spent platinum catalyst supported on activated carbon (Pt/AC) as well as the chemically treated spent catalysts were studied to understand their catalytic and adsorption activities. Sulfuric aqueous acid solution (0.1N, H₂SO₄) was used to regenerate the spent Pt/AC catalyst. The physico-chemical properties of the catalysts in the spent and chemically treated states were analyzed by using nitrogen adsorption–desorption isotherm and elemental analysis (EDX). The gravimetric adsorption and the light-off curve analysis were employed to study the BTX adsorption and oxidation on the spent catalyst and its modified Pt/AC catalysts. The experimental results indicate that the spent Pt/AC catalyst treated with the H₂SO₄ aqueous solution has a higher toluene adsorption and conversion ability than that of the spent Pt/AC catalyst. A further studies of H₂SO₄ treated Pt/AC catalyst on their catalytic and heterogeneous adsorption behaviours for BTX revealed that the activity of the H₂SO₄ treated Pt/AC catalyst follows the sequence of benzene>toluene>o-xylene. The adsorption equilibrium isotherms of BTX on the H₂SO₄ treated Pt/AC were measured at different temperatures ranging from 120 to 180°C. To correlate the equilibrium data and evaluate their adsorption affinity for BTX, the two sites localized Langmuir (L2m) isotherm model was employed. The heterogeneous surface feature of the H₂SO₄ treated Pt/AC was described in detail with the information obtained from the results of isosteric enthalpy of adsorption and adsorption energy distributions. Furthermore, the activity of H₂SO₄ treated Pt/AC about BTX was found to be directly related to the Henry's constant, isosteric enthalpy of adsorption and adsorption energy distribution functions.

Keywords: Adsorption; Catalytic oxidation; Platinum; Activate carbon; Pretreatment; VOCs

Investigation of oxide catalysts activity in the NO_x neutralisation with organic reductants by W. Turek; A. Plis; P. Da Costa; A. Krzton (pp. 5572-5575).

Temperature-programmed desorption of NO (TPD) and temperature-programmed reduction of NO by propene and ethanol (TPSR) over the catalyst with redox properties and the structure of spinels – Co₃O₄ and CoFe₂O₄ – were investigated.The TPD experiments can determine the temperature range in which the deNO_x proceeds and provide information about the heat of adsorption of NO on the surface of catalysts. The values of the adsorption heat are much higher in the case of the catalyst with weaker redox properties (CoFe₂O₄), because of stronger bonds between the adsorbate and the surface of catalyst. The TPD and TPSR experiments show that ethyl alcohol is a more active reductant in the deNO_x process than propene. The maximum of NO_x conversion is higher with ethyl alcohol used as a reductant in both cases of investigated catalysts. Moreover, the temperature of the maximum degree of NO_x reduction is lower in the case of alcohol used as an reductant. Co₃O₄ is a more active and suitable catalyst for the deNO_x process than CoFe₂O₄.

Keywords: Selective catalytic NO; _x; reduction by propene or ethyl alcohol; Temperature-programmed desorption of NO (TPD); Temperature-programmed surface reaction of NO (TPSR); Spinels

Modifications induced by potassium addition on chromia/alumina catalysts and their influence on the catalytic activity for the oxidative dehydrogenation of propane by E. Rombi; D. Gazzoli; M.G. Cutrufello; S. De Rossi; I. Ferino (pp. 5576-5580).

The oxidative dehydrogenation of propane was investigated on K-containing chromia/alumina catalysts, with nominal Cr and K loadings of 10 and 0–2wt%, respectively. Their chemical composition, structure, texture, nature of surface species, redox features and surface acidity were determined. Catalytic behaviour was investigated in a continuous-flow micro-reactor under different conditions. Besides the nature and concentration of the chromium species, potassium addition was found to affect the reducibility of the catalysts as well as their acid surface features. Such modifications were found to condition the catalytic behaviour, which appeared somewhat peculiar in comparison with that of the catalytic systems reported in literature.

Keywords: Propane; Oxidative dehydrogenation; Chromia/alumina; Acidity; Potassium

Surface and catalytic properties of potassium-modified cobalt molybdenum catalysts for ammonia synthesis by Dariusz Moszyński; Roman Jędrzejewski; Janusz Ziebro; Walerian Arabczyk (pp. 5581-5584).

The influence of potassium addition on the structural, catalytic and surface properties of the cobalt molybdenum nitride was studied. The measurements of the catalytic activity and the specific surface area as well as the phase analysis with the use of X-ray diffraction were performed. The mixtures of Co₃Mo₃N and Co₂Mo₃N phases have been found to constitute the samples. The concentration ratio between the Co₂Mo₃N and Co₃Mo₃N phases is notably influenced by potassium admixture. The specific surface area of the catalysts changes also with the Co₂Mo₃N/Co₃Mo₃N ratio. The catalytic activity of the catalysts in the ammonia synthesis carried out at 400°C and under the pressure of 10MPa can be increased up to 2.4 times by the addition of potassium compounds. There is the optimal range of potassium concentration between 0.8 and 1.2wt.%.

Keywords: Cobalt molybdenum nitride; Ammonia synthesis; Specific surface area; Catalyst

Studies of catalytic process of complete oxidation of methane by SSITKA method by Marek Rotko; Andrzej Machocki; Beata Stasinska (pp. 5585-5589).

This paper presents the results obtained by means of the steady state isotopic transient kinetic analysis for complete methane oxidation over the Pd(PdO)Al₂O₃ catalyst. The average surface life-time and surface concentration of methane and carbon dioxide were determined. It was found out that on the palladium catalyst there are adsorbed small amounts of methane (which does not take part in the process of oxidation) only at the temperature corresponding to the starting point of methane oxidation. Additionally, in the steady state of methane oxidation on the palladium catalyst there are present two different kinds of carbon dioxide: short- and long-resided on the catalyst surface. The average surface life-time of both kinds of carbon dioxide decreases with temperature. The surface concentration of long-resided carbon dioxide increases with temperature whereas the small maximum at about 380°C is noticed for the surface concentration of short-resided carbon dioxide.

Keywords: Complete methane oxidation; Palladium catalyst; SSITKA; CO; ₂; surface concentration; CO; ₂; surface life-time

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Applied Surface Science (v.256, #17)

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Applied Surface Science (v.256, #17)