Analysis of relative pressure range influence on the identification quality during computer identification of adsorption system parameters by employing the new multilayer adsorption models

The aim of this work has been to analyze the problems related to the identification of microporous structure parameters of carbonaceous materials. The new methods for microporous structure parameters identification have been explored with special focus on the influence of the analyzed relative pressure range on the reliability of parameters identification. For that purpose, the adsorption isotherm of nitrogen on active carbon for different ranges of relative pressures p/p₀ was analyzed. The conducted research was to provide for an answer to the question of whether the range of the analyzed relative pressures has any effect on the quality of adsorption system parameters identification, as well as what range of the relative pressure permits execution of the reliable identification of microporous structure parameters.     

Transverse momenta of helium fragments in gold fragmentation at 10.6 GeV/nucleon

The transverse momentum (p_t) distributions of helium fragments from gold fragmentation on different nuclei of nuclear emulsion have been measured and a clear increase of average p _t with target mass is seen. The p _t distributions can be parameterized by a sum of three exponential functions of the form $\sim {\rm exp}(-p_{t}^{2}/B_{i})$ . The differences in p _t distributions in interactions on different targets can be explained by different contributions of the three exponential functions. These contributions depend on the projectile breakup in the collision, and for a given degree of the projectile breakup do not depend on the target mass.     

Transverse momentum distribution in Pomeron-Pomeron collisions at the CERN ISR

Proton-proton interactions which result in a central cluster of massM _x and two quasi-elastically scattered protons are generally described by Pomeron-Pomeron scattering. A study of this process at ISR energies with the Split Field Magnet detector is carried out in terms of transverse momentum behaviour for the centrally produced system of particles. The inclusivep _T distribution for central hadrons is measured up to 3 GeV/c. Forp _T <1.2 GeV/c, thep _T distribution is exponential. Using a subsample of exclusive events, this exponential shape is shown to originate from a phase-space-like decay ofM _x when convoluted with a transverse component of the pomeron momentum. In the highp _T range, the shape of thep _T distribution strongly depends on Feynman-x of the scattered protons in a way that can be described by hard parton scattering.     

Adsorption of gas mixtures on heterogeneous surfaces: The integral representation for a monolayer total adsorption isotherm

The authors extended the integral equation for a one-component adsorption isotherm on to n-component adsorption from gaseous mixtures. It appears that the n-component adsorption isotherm on heterogeneous surfaces can be presented as a multiple integral. Two methods were used for evaluation of the surface heterogeneity with regard to a gas mixture. The first method is based on the n-dimensional gaussian energy distribution. The second one concerns the extension of our method for studying adsorption systems of high surface heterogeneity. Two-component adsorption systems have been analyzed in details.     

Wetting transitions at triple points; A study based upon the analysis of stepwise adsorption isotherms

This adsorption isotherm study finds that ethylene adsorption on PbI₂ is limited to only a few layers at T<T_3t (the triple point temperature of bulk ethylene) but that almost unlimited adsorption can take place as T_3t, is approached. This behaviour is qualitatively identical to the behaviour of the ethylene/graphite system previously reported. In both cases wetting by ethylene is incomplete below T_3t since the adlayers formed have an orientational order which is in compatible with that which is found in the bulk solid ethylene. However, C₂H₄ shows a strong tendency to wetting somewhat below its bulk triple point temperature because it can form a liquid or at least an orientationally disordered solid film of limited thickness. The similarities and differences between these two systems are discussed. In addition, we discuss in general systems for which wetting is temperature dependent. The first part of this paper is devoted to outlining in detail how stepwise adsorption isotherms on powdered samples can be used to give information about wetting of the exposed basal face. The merits and limitations of this method are discussed in the context of the ethylene/PbI₂ example.     

Preparation of activated carbon from Enteromorpha prolifera and its use on cationic red X-GRL removal

Enteromorpha prolifera was pyrolyzed to prepare activated carbon using chemical activation by zinc chloride. The effect of activation parameters such as activation temperature, weight ratio (Enteromorpha prolifera to ZnCl₂), and activation time was investigated. The BET results showed that the surface area and pore volume of activated carbons were achieved as high as 1722 m²/g and 1.11 cm³/g, respectively, in the optimal activation conditions. Batch adsorption studies were carried out to study the adsorption properties of cationic red X-GRL onto activated carbon by varying the parameters like initial solution pH, contact time, and temperature. The kinetic studies showed that the adsorption data followed a pseudo second-order model. The isotherm analysis indicated that the adsorption data could be represented by the Langmuir isotherm model. The Langmuir monolayer adsorption capacity of cationic red X-GRL was estimated as 263.16 mg/g at pH 6.0.     

Preparation, characterization and dye adsorption properties of γ-Fe2O3/SiO2/chitosan composite

A γ-Fe₂O₃/SiO₂/chitosan composite was prepared by water-in-oil emulsification, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Effects of various factors, including adsorbent dosage, initial dye concentration, solution pH, and competing anions, on the adsorption of methyl orange from aqueous solutions by the resulting composite were studied by batch adsorption experiments. The adsorption kinetics was found to follow the pseudo-second-order kinetic model, and intraparticle diffusion was related to the adsorption, but not as a sole rate-controlling step. The equilibrium adsorption data were well described by the Freundlich isotherm model. Evaluation of the thermodynamic parameters ΔG°, ΔH°, and ΔS° revealed that the adsorption process was naturally feasible, spontaneous, and exothermic. The composite was proven to be efficient, suitable and promising for the removal of methyl orange from aqueous solutions since it has a relatively higher adsorption capacity than other low-cost adsorbents.     

Kinetic and theoretical studies of metal ion adsorption in KDP solution

Metal ion adsorption in saturated aqueous potassium dihydrogen phosphate solution was analyzed using kinetic, equilibrium model and computational chemistry approaches. The isotherm constants (K_F and n) in the Freundlich model and the first order Lagergren kinetic model parameter k assist with a general understanding of the fundamental adsorption behavior of trivalent and divalent metal ions. The electrostatic force based on electrostatic potential distribution was found to be an essential feature for metal ion adsorption via a correlation between the ESP values of each metal ion and these experimental parameters.     

Removal of lead(II) by adsorption onto Viscumalbum L.: Effect of temperature and equilibrium isotherm analyses

The removal efficiency of Viscumalbum L. from lead containing aqueous solutions was investigated. The effect of adsorbent mass, pH of solution, initial Pb(II) concentration and temperature was investigated using a batch adsorption technique. The optimum pH for Pb(II) adsorption was found as 3.0 for Viscumalbum L. Results were analyzed by the Langmuir, Freundlich, Temkin and Harkins-Jura, equation using linearized correlation coefficient at different temperature. The characteristic parameters for each isotherm have been determined. The Langmuir model agrees very well with experimental data than the other models. According to Langmuir isoterm, the monolayer saturation capacity (Q_o) is 769.23 mg/g at 25 °C. Models and the isotherm constant were evaluated depending on temperature. Thermodynamic parameters such as ΔH^o, ΔS^o and ΔG^o were calculated. The adsorption process was found to be endothermic and spontaneous. The experimental data were analyzed using the first- and the second-order kinetic models. The rate constants of adsorption for both kinetics models have been calculated. The second-order model provides the best correlation of the data.     

Unified model of energy transfer for arbitrary Franck-Condon offset and temperature

The Huang-Rhys-Pekar W_p(T, S) function is known to give the thermal-Franck-Condon (FC) weight of single-center radiative and non-radiative transitions for arbitrary energy mismatch p?ω₀, temperature T, and FC offset S. The thermal-FC weight for energy transfer is shown also to be W_p(T, S), with S enlarged to be the sum of the S values of the energy donor and energy acceptor. This result generalizes an earlier result of Miyakawa and Dexter for low-temperature Poisson functions. The W_p function with enlarged S is equivalent to the overlap of the donor emission and acceptor absorption bands in the Förster-Dexter theory. Experimental verification is good except for the p dependence of non-radiative and energy-transfer rates for S small (e.g. 4f → 4f transitions). Here, if the smooth, exponential p dependences (exponential energy-gap laws) that have been drawn through many 4f → 4f transition rates in certain hosts (Y₂O₃, LaF₃) are fitted with a W_p(T, S) function with a single S value, this S value is too large to describe 4f → 4f transitions.     

Spectra of negative particles and photons in collisions of p−W and16O−W at 200 GeV/u

p _⊥ spectra of negative particles were measured for p?W and¹⁶O?W collisions at 200 GeV/u in the rapidity range 0.9<y<1.9. Within the systematic errors of 20% the spectra are identical in the range 0.05<p _⊥<2.0 GeV/c. The p?W and¹⁶O?W spectra exhibit an exponential shape forp _⊥ >250 MeV/c. This is consistent with previous p?A data, but there is a significant excess above this exponential at lowerp _⊥. Photon spectra were measured using a conversion method. Theirp _⊥ distribution agrees in shape with the sum of known hadronic γ-sources.     

Adsorption study of dimethylaminostyryl benzazoles onto Na-montmorillonite

The adsorption of 2-(4′-dimethylaminostyryl)benzoxazole (DMASBO) and its benzothiazole analogue (DMASBT) onto Na-montmorillonite (Na⁺-MMT) was studied. The adsorption data have been fitted with Freundlich and Dubinin-Radushkevich (D-R) equation to find the characteristic parameters of each model. From D-R isotherm, it was concluded that the adsorption is of chemical nature. The equilibrium adsorption constant, K_c, was determined and has been used to calculate the enthalpy and entropy of the adsorption process. The mechanism of the adsorption has been investigated by fluorescence, IR, X-ray and ESR spectroscopic measurements. These measurements indicate oxidation of the styryl dyes by the Lewis acidic sites of the clay and formation of radical cations at Na⁺-MMT surface without intercalation into the interior.     

Adsorption equilibrium and kinetics of dibenzothiophene from n-octane on bamboo charcoal

The adsorption of the model sulfur compound dibenzothiophene (DBT) from n-octane solution on to bamboo charcoal (BC) was investigated. The equilibrium and kinetics of DBT adsorption on BC were examined. Adsorption isotherm of DBT on BC was determined and correlated with two well-known isotherm equations (Langmuir and Freundlich). The equilibrium data for DBT adsorption fitted the Freundlich model well. Two simplified kinetic models including pseudo first-order and pseudo second-order equations were selected to follow the adsorption processes. The adsorption of DBT on BC can be best described by a pseudo second-order equation. The parameters of this best-fit kinetic model were calculated and discussed.     

Isothermal adsorption kinetics on heterogeneous surfaces

Adsorption kinetics on energetically heterogeneous surfaces under isothermal conditions is analyzed using the uniform energy distribution model. Considering the quasi-equilibrium of surface diffusion between the adsorption sites with different energy, the kinetic equations dΘ/dt=(k_ap−A_dK_diff)(1−Θ) for first-order adsorption and dΘ/dt=k_ap(1−Θ)²−A_dK_diffΘ(1−Θ) for dissociative adsorption are obtained, where K_diff is a coefficient describing the surface diffusion equilibrium, which depends on the coverage and the energy distribution. Under isochoric conditions with p decreasing due to adsorption, surface diffusion accelerates the rate towards equilibrium significantly, as observed in static calorimetric adsorption experiments. An approximate solution in Lagergren form is derived for this condition.     

An ion-imprinted amino-functionalized silica gel sorbent prepared by hydrothermal assisted surface imprinting technique for selective removal of cadmium (II) from aqueous solution

A new ion-imprinted amino-functionalized silica gel sorbent was synthesized by the hydrothermal-assisted surface imprinting technique using Cd²⁺ as the template, 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AAAPTS) as the functional monomer, and epichlorohydrin as the cross-linking agent (IIP-AAAPTS/SiO₂) for the selective removal of Cd²⁺ from aqueous solution, and was characterized by FTIR, SEM, nitrogen adsorption and the static adsorption-desorption experiment method. The specific surface area of the IIP-AAAPTS/SiO₂ sorbents was found to be 149 m² g⁻¹. The results showed that the maximum static adsorption capacities of IIP-AAAPTS/SiO₂ sorbents by hydrothermal heating method and by the conventional heating method were 57.4 and 31.6 mg g⁻¹, respectively. The IIP-AAAPTS/SiO₂ sorbents offered a fast kinetics for the adsorption and desorption of Cd(II). The relative selectivity coefficients of IIP-AAAPTS/SiO₂ sorbents for Cd²⁺/Co²⁺, Cd²⁺/Ni²⁺, Cd²⁺/Zn²⁺, Cd²⁺/Pb²⁺ and Cd²⁺/Cu²⁺ were 30.68, 14.02, 3.00, 3.12 and 6.17, respectively. IIP-AAAPTS/SiO₂ sorbents had a substantial binding capacity in the range of pH 4-8 and could be used repeatedly. Equilibrium data fitted perfectly with Langmuir isotherm model compared to Freundlich isotherm model. Kinetic studies indicated that adsorption followed a pseudo-second-order model. Negative values of ΔG° indicated spontaneous adsorption and the degree of spontaneity of the reaction increased with increasing temperature. ΔH° of 26.13 kJ mol⁻¹ due to the adsorption of Cd²⁺ on the IIP-AAAPTS/SiO₂ sorbents indicated that the adsorption was endothermic in the experimental temperature range.     

Comments on the dynamical properties of iron pentacarbonyl,Fe(CO)5, adsorbed on (0001) graphite

A fraction of a monolayer of Fe(CO)₅ was deposited on a clean Papyex stack following an adsorption vapor pressure isotherm. Mössbauer spectra for k_γ parallel and perpendicular to the film surface yield evidence of a first-order phase transition at T ～- K. The asymmetry of the spectrum suggests a possible average list of the molecular axis of ~50° to the surface normal.     

Electrochemical and theoretical investigation on the corrosion of aluminium in acidic solution containing some Schiff bases

The effect of newly synthesised three Schiff bases—2-[2-aza-2-(5-methyl(2-pyridly))vinyl]phenol, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]-4-bromophenol, 2-[2-aza-2-(5-methyl(2-pyridly))vinyl]-4-chlorophenol—on the corrosion behaviour of aluminium in 0.1 M HCl were investigated using potentiodynamic polarisation, electrochemical impedance spectroscopy and linear polarisation methods. Polarisation curves indicate that all studied Schiff bases were acting as mixed type inhibitors. All measurements show that inhibition efficiencies increase with increase in inhibitor concentration. This reveals that inhibitive actions of inhibitors were mainly due to adsorption on aluminium surface. Adsorption of these inhibitors follows Langmuir adsorption isotherm. Thermodynamic parameters of adsorption (K_ads, ΔG_ads) of studied Schiff bases were calculated using Langmuir adsorption isotherm. The variation in inhibition efficiency values depends on the type of functional groups substituted on benzene ring. It was found that the presence of bromine and chlorine atoms in the molecular structure of studied Schiff bases facilitate the adsorption of molecule on aluminium surface.The correlation between the inhibition efficiencies of studied Schiff bases and their molecular structure has been investigated using quantum chemical parameters obtained by MNDO semi-empirical SCF-MO methods. These results indicate that adsorption of studied Schiff bases depends on the charge density of adsorption centres and dipole moments.     

Kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain from aqueous solutions

Spent grain, a main by-product of the brewing industry, is available in large quantities, but its main application has been limited to animal feeding. Nevertheless, in this study, spent grain modified with 1 M NaCl solution as a novel adsorbent has been used for the adsorption of Pb(II) in aqueous solutions. Isotherms, kinetics and thermodynamics of Pb(II) adsorption onto modified spent grain were studied. The equilibrium data were well fitted with Langmuir, Freundlich and Dubinin-Radushkevick (D-R) isotherm models. The kinetics of Pb(II) adsorption followed pseudo-second-order model, using the rate constants of pseudo-second-order model, the activation energy (E_a) of Pb(II) adsorption was determined as 12.33 kJ mol⁻¹ according to the Arrhenius equation. Various thermodynamic parameters such as ΔG^ads, ΔH^ads and ΔS^ads were also calculated. Thermodynamic results indicate that Pb(II) adsorption onto modified spent grain is a spontaneous and endothermic process. Therefore, it can be concluded that modified spent grain as a new effective adsorbent has potential for Pb(II) removal from aqueous solutions.     

Polar curves for transmission ellipsometry

For three-phase ambient-film-substrate systems, the ratio ?_T = T_p/T_s of the complex amplitude-transmission coefficients T_p and T_s for light polarized parallel (p) and perpendicular (s) to the plane of incidence is related to a complex exponential function of film thickness d by a bilinear transformation. This observation leads to elucidation of the nature of the complex plane polar curves of the function ?_T(d), where the film thickness is variable and the angle of incidence is fixed. In particular, the polar curve ?_T(d) for a transparent ambient-film-substrate system studied by transmission ellipsometry is shown to be exactly a circle.