Study of adsorption from solutions by frontal chromatography

Summary The automatic frontal chromatography installation was described. By this chromatographic method the adsorption isotherm of benzene from n-heptane solutions on hydroxylated surface of silica with various porosity has been determined. This investigation was performed at different flow rates of eluent and in a wide range of concentrations. The isotherm of adsorption obtained by this chromatographic method has been compared with the results of the static measurements. The coincidence of adsorption isotherms measured at the various flow rates are shown to be a criterion of proximity the chromatographic process to the equilibrium.     

Multilayer adsorption of alcohols from benzene/n-heptane mixtures on silica gel

An equation for multilayer adsorption from multicomponent liquid mixtures on solid surfaces¹ has been examined. For this purpose experimental adsorption data for four alcohols from benzene/n-heptane mixture on silica gel have been measured. Average number of the adsorbed layers, heterogeneity parameter and capacity of the surface phase have been evaluated by using the equation mentioned above.

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Mehrschichten-Adsorption von Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel

Zusammenfassung Eine Gleichung für Mehrschichten-Adsorption an festen Oberflächen¹ aus Mehrkomponentenlösungen wurde getestet. Zu diesem Zweck wurden experimentelle Daten für die Adsorption von vier Alkoholen aus Benzol/n-Heptan-Mischung an Silica Gel herangezogen. Der Mittelwert für die Anzahl der Adsorptionsschichten, der Heterogenitätsparameter und die Kapazität der Oberflächenphase wurde aus dieser Gleichung berechnet.

     

Adsorption from ternary liquid mixtures on silica gel and aluminium oxide

Formation of mixed adsorbed layers was tested for ternary liquid mixtures containing methanol or acetone and the binary solvent benzene+n — heptane. The specific excess adsorption isotherms from the liquid phase were measured on silica gel, silanized silica gel and aluminium oxide. The experimental adsorption data are discussed on the basis of the changes in the mixed solvent composition.     

Thermodynamics of adsorption of organic liquids on Ni-modified solid obtained from collodal silica

Summary In order to reduce the well known silica surface inhomogeneity and to get a material suitable for selective chromatographic separations, a modified variety of the material was prepared by a controlled sorption of Ni²⁺ ions at the solid surface; its adsorption properties were then investigated using the GSC method. Since the starting material was of very high purity, it was possible to follow the influence of Ni²⁺ ion on the adsorption of various organic liquids, including n-alkanes, cyclohexane, benzene and halomethanes. Adsorption experiments, spanning zero surface coverage and the finite concentration region, were performed in the temperature range from 333 to 443 K. Both the surface activity change resulting from the modification and the possible interactions between the organic substances and the prepared adsorbent were examined using the standard free energy change of adsorption in zero coverage conditions. The adsorption isotherms of all the adsorbates listed were obtained using the Elution by Characteristic Point (ECP) technique and the data were fitted to the BET equation. To get a better insight into the adsorption process in the finite concentration region, the thermodynamic parameters of adsorption were determined and are discussed in terms of surface coverage.     

Adsorption of organic liquids on alkaline earth-metal modified silica

Summary Adsorption properties of alkaline earth-metal modified silica beads were investigated by the gas-solid chromatography (GSC) method. Silica beads, obtained from colloidal material, were characterized by their surface areas, crystallinity and amount of sorbed alkaline earth cations. Retentions of several aliphatic, alicyclic, chlorinated, and aromatic compounds were measured in the temperature range from 373 to 453 K.The gas/solid partition coefficients, K₅, and the related thermodynamic functions at zero surface coverage were determined. The results show that the specific surface areas of modified silica samples remain practically constant, whereas the modification leads to a decrease of silica surface heterogeneity.     

Adsorption of di-2-pyridyl ketone salicyloylhydrazone on silica gel: characteristics and isotherms

The adsorption of DPKSH onto silica gel was investigated, at 25±1 °C and pH 1, 4.7 and 12. For the same DPKSH concentration interval, the minimum required time of contact for adsorption maximum at pH 4.7 was smaller than at pH 1 and the maximum amount of DPKSH adsorbed per gram of silica at pH 1 is smaller than at pH 4.7. At pH 12 the DPKSH adsorption onto silica gel was not significant. The adsorption data followed Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherms. The maximum amount of solute adsorbed (m_ads^max) and the adsorption constant, K_L, were derived from Langmuir isotherm. The Freundlich constants 1/n and K_F related, respectively, to the energetic heterogeneity of adsorption sites and an empirical constant were evaluated. The mean sorption free energy (E) of DPKSH adsorption onto silica gel was calculated from D-R isotherm indicating a physical adsorption mode. Finally, conductimetric titrations showed the silica particle basicity and acidity as 0.002 and 0.3 mmol g⁻¹, respectively.     

HPLC study of the adsorption from solutions on two silicagels

Summary In this paper, we report and discuss the adsorption isotherms of hydro-organic mixtures and of compounds used as mobile phase in reversed phase and normal phase high performance liquid chromatography (RP-HPLC and NP-HPLC, respectively). This work is the first attempt to study the solid-liquid interface between two types of chromatographic silica surfaces and pure organic adsorbates from water and from organic eluents by HPLC. Frequently, among the dynamic techniques the method of choice for the measurement of an adsorption isotherm is frontal analysis. We suggest here the combination of the technique based on peak asymmetry calibration and peak profiles, which allows calculations directly from integration data. The group of systems studied permits the analysis of the intermolecular interactions on the silica surface. Particular attention was given to the system methanol-water and the measurement of the adsorption ofn-octanol from methanol on RP-silica was also carried out.     

Multilayer effects in adsorption of alcohols from benzene andn-heptane on silica gel

Experimental data for the title systems are compared with calculations based on theoretical adsorption parameters.

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Mehrschichteffekte bei der Adsorption von Alkoholen aus Benzol undn-Heptan auf Silicagel (Kurze Mitteilung)

Zusammenfassung Für die im Titel genannten Systeme werden experimentelle Daten mit Berechnungen verglichen, die auf theoretischen Parametern basieren.

     

New procedure of silica gel surface modification preparation of gaseous standard mixtures for calibration purposes

The new type of silica gel surface modification with using the trimethylamine as a reagent is described. The samples of chemically modified silica gel have been used for generation of gaseous standard mixtures (methyl chloride as a measurand) using the technique of thermal decomposition of the surface compound. The main aim of the research was to check the suitability of the new type of silica gel surface modification for obtaining methyl chloride as a measurand of gaseous standard mixture. The gaseous standard mixture obtained with using this technique was used for calibration of a thermal desorber-gas chromatography-flame ionization detector (TD-GC-FID) system. The homogeneity of coverage of silica gel surface with the immobilized compound has been evaluated. The full uncertainty budget of determination of liberated amount of methyl chloride has been calculated. The average amount of methyl chloride liberated from the unit sample of chemically modified silica gel is 3.59 +/- 0.13 mg g(-1). The influence of the modification way on the amount of liberated analyte has also been determined.     

Solubility of benzil in binary alkane + dibutyl ether solvent mixtures. Comparison of predictive expressions derived from the nearly ideal binary solvent model

Experimental solubilities are reported for benzil dissolved in six binary mixtures containing dibutyl ether with hexane, heptane, octane, cyclohexane, methylcyclohexane, and 2,2,4-trimethylpentane at 25°C. Results of these measurements are compared to the predictions of equations developed previously for solubility in systems of nonspecific interactions. The most successful equation in terms of goodness of fit involved a volume fraction average of the excess Gibbs energies relative to the Flory-Huggins model, and predicted the experimental solubilities in the six systems studied to within an overall average absolute deviation of 3.4% and with a maximum deviation of 6.0%.     

Adsorption of polar substances from binary and ternary mixtures on silica gel

The adsorption isotherms of acetone and methyl ethyl ketone from binary and ternary mixtures in benzene and n-heptane on silica gel were measured. The experimental adsorption data are discussed on the basis of changes of the composition of mixed solvent (benzene + n-heptane) in ternary mixtures. It has been found that the different structures of the surface phase correspond to the system investigated. The marked dependence of the adsorption on the solvent character is demonstrated. For benzene and ternary (ketone + benzene + n-heptane) mixtures a mixed character of the surface phase is observed whose composition is determined by competition of liquid components for silica surface as well as its tendency to complex. Bilayer model of the surface phase gives a good representation of the experimental data for binary systems benzene + ketone.     

Synthesis and characterization of silica gel from siliceous sands of southern Tunisia

The present work aimed to achieve valorization of Albian sands for the preparation of sodium silicates that are commonly used as a precursor to prepare silica gel. A siliceous sand sample was mixed with sodium carbonate and heated at a high temperature (1060 °C) to prepare sodium silicates. The sodium silicates were dissolved in distilled water to obtain high quality sodium silicate solution. Hydrochloric acid was then slowly added to the hydrated sodium silicates to obtain silica gel. The collected raw siliceous sands, as well as the prepared silica gels, were characterized by different techniques, such as X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (DSC). XRF confirmed that the detrital sand deposits of southern Tunisia contain high amounts of silica, with content ranging from 88.8% to 97.5%. The internal porosity varied between 17% and 22%, and the specific surface area was less than 5 m²/g. After the treatment described above, it was observed that the porosity of the obtained silica gel reached 57% and the specific surface area exceeded 340 m²/g. Nitrogen adsorption isotherms showed that the prepared silica gels are microporous and mesoporous materials with high adsorption capacities. These results suggest that the obtained silica gels are promising materials for numerous environmental applications.     

Optimum conditions for the separation of nucleobases and nucleosides on unmodified silica by HPLC

Summary The retention behaviour of nucleobases and nucleosides on unmodified silica with dichloromethane-methanol-water mixtures has been systematically investigated. The degree and order of retention can be varied over a wide range by changing the pH, the type and concentration of the acidic additives and by the methanol and water content of the mobile phase. The retention process cannot be considered as simple adsorption but rather as a very complex mixed distribution process of adsorption and absorption including the involvement of ion-pair formation. Further data on the effect of the type of silica (source of supply) on retention behaviour, column efficiency and column reproducibility are reported. The practical application of unmodified silica for the separation of nucleobases and nucleosides is demonstrated by the analysis of a hydrolysate of calf thymus DNA.     

A simple method for determining the multilayer effects in adsorption of alcohols on silica gel

The excess adsorption isotherms ofn-pentanol, pentan-2-ol and 2-methylbutan-2-ol from binary and ternary solutions in benzene andn-heptane were measured. Experimental adsorption data are discussed in terms of a multilayer model of the surface phase. The main assumption of this model is that the surface layers being near the solid surface contain the molecules of the preferentially adsorbed component only. The phase-exchange reaction of molecules between bulk phase and last surface layer has been taken into account.On the basis of this theory it has been established for the investigated systems that the surface phase contains three molecular layers. Simultaneously appropriate surface phase capacities were determined.

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Eine einfache Untersuchungsmethode für Mehrschicht-Effekte bei der Adsorption von Alkoholen an Kieselgel

Zusammenfassung Die Adsorptionsisothermen binärer und ternärer flüssiger Mischungen vonn-Pentanol, 2-Pentanol oder 2-Methyl-2-butanol in Benzol und/odern-Heptan wurden bezüglich Kieselgel gemessen. Die experimentellen Daten der Adsorption wurden mittels des Mehrschichts-Modells der Oberflächenphase diskutiert. Die Hauptvoraussetzung dieses Modells ist die Annahme, daß die Oberflächenschichten, die sich in der Nähe des Kieselgels befinden, nur Moleküle der bevorzugt adsorbierten Komponente enthalten. Es wurde auch die Phasen-Austauschreaktion von Molekülen zwischen Phaseninnerem und der letzten Oberflächenschicht in Betracht gezogen.Auf der Basis dieser Theorie wurde für die untersuchten Systeme festgestellt, daß die Oberflächenphase aus drei Molekülschichten besteht. Außerdem wurden die ermittelten Volumina der Oberflächenphase berechnet.

     

Adsorption from solutions of nonelectrolytes on heterogeneous solid surfaces: A four-parameter equation for the excess adsorption isotherm

A four-parameter single-solute adsorption isotherm equation is generalized to the adsorption of binary liquid mixtures of nonelectrolytes. This equation comprises all isotherms being a simple extension of theEverett isotherm to liquid adsorption on heterogeneous solid surfaces. The benzene—cyclohexane excess adsorption data on silica gel are studied by using this new equation.

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Adsorption aus Lösungen von Nichtelektrolyten an heterogenen festen Oberflächen: Eine Vierparametergleichung für die Excess-Adsorptions-Isotherme

Zusammenfassung Es wird eine Vierparameter-Isothermengleichung für binäre Lösungen von Nichtelektrolyten diskutiert. Diese Gleichung umfaßt alle Isothermen vom Typ der einfachen Erweiterung derEverett-Isotherme für Flüssig-Adsorption auf heterogenen festen Oberflächen. Die Daten für die Adsorption von Benzol—Cyclohexan werden mittels dieser neuen Gleichung behandelt.

     

Adsorption of cesium using mesoporous silica gel evenly doped by Prussian blue nanoparticles

In this paper, a novel mesoporous silica gel evenly doped by Prussian blue nanoparticles (PBMSG) was successfully synthesized by using N,N-dimethylamide as template with a large Barrett-Emmett-Teller (BET) surface area of 505 m²/g and an average pore size of 2.9 nm. The static adsorption experiments showed that the equilibration time of PBMSG for Cs⁺ was about 30 min. The adsorption isotherm of PBMSG for Cs⁺ accorded with Langmuir model and the theoretical maximum adsorption capacity was 80.0 ± 2.9 mg/g. When the initial concentration of Cs⁺ was 1.00 mg/L, the adsorption partition coefficient K_d could reach 3.5 × 10⁴ mL/g After adsorption, Cs⁺ could be eluted by dilute hydrochloric acid (pH 2) with an efficiency of 89.8%, while no K⁺, Fe³⁺, Fe²⁺ was eluted. PBMSG exhibited good selectivity toward Cs⁺ and Rb⁺. In the presence of high concentration of K⁺, the selective adsorption of PBMSG could change the mass ratio of K⁺, Rb⁺ and Cs⁺ from 96.63:0.83:1.00–1.12:0.73:1.00. The separation of Cs⁺ and Rb⁺ from K⁺ with similar concentration (100 mg/g) was realized by column experiment. This indicated that PBMSG was suitable for rapid recovery of low concentration of rubidium and cesium from complex matrixes, such as wastewater and salt lake brine, etc.     

Adsorption effects in gel permeation chromatography: The application of binary mobile phases

Summary The influence of the adsorption properties of the column packing on the elution mechanism of macromolecules was investigated. Experimentally determined elution volumes of polystyrene standards in different mobile phases were compared with computed theoretical plots assuming (a) the pure steric exclusion mechanism; (b) mixed steric exclusion and adsorption mechanism.     

Chromatographic study of adsorption from binary and ternary solutions

Adsorption of benzene, anisole, and nitrobenzene on hydroxylated silica gel from binary and ternary solutions (adsorbate--n-hexane and adsorbate--n-hexane--terahydrofuran) was studied by HPLC. The equation that describes the adsorbate retention as a function of its concentration in binary and ternary solutions was proposed. The equation makes it possible to calculate the adsorption isotherms and adsorption equilibrium constants directly from chromatograms using the retention parameters and equilibrium concentrations of the adsorbate in the mobile phase.