Displacement processes on hydrophilic/hydrophobic surfaces in 1-propanol-water mixtures

Selective adsorption of 1-propanol-water mixtures was investigated on adsorbents of various surface character. The enthalpy of displacement of 1-propanol by water was studied on graphitized PRINTEX-80, K-60 silicagel, and n-alkylammonium vermiculites. The free enthalpy and entropy isotherms of displacement were derived. The adsorption between the silicate layers of hydrophobic vermiculites was followed by x-ray measurements, and thermodynamic functions were calculated for the structural changes in the adsorption layers. Formation of alcohol-water clusters on the surfaces plays an important role.     

酪氨酸在活性炭/水界面上的吸附

研究了不同pH值介质中酪氨酸在活性炭上的吸附行为.结果表明,pH值4.2～6.1时吸附量较大,在酪氨酸的等电点时吸附量最大;酪氨酸被吸附的主要形式是兼性离子;酪氨酸离子靠VanderWaals力吸附在活性炭/水界面上.用介质pH值对酪氨酸溶解度的影响和活性炭的表面性质解释了实验结果     

Adsorption of nitrobenzene andn-pentanol from aqueous solution on hydrophilic and hydrophobic clay minerals

The sorption of nitrobenzene andn-pentanol from dilute aqueous solution on swelling clay minerals and their organophilized derivatives (organo clays) was studied. Adsorption excess isotherms were obtained by the immersion method. The basal spacings of the clay minerals were determined by X-ray diffraction measurements. By combining these two independent methods, composition and structure of the interlamellar space could be calculated. On the hydrophilic surface of montmorillonite negative adsorption of the organic component was observed at low molar fractions of nitrobenzene or pentanol, i.e., water was preferentially adsorbed. On organophilized montmorillonite and vermiculite adsorption of nitrobenzene and pentanol was positive over the whole range of liquid composition. The amount of interlamellar alkyl chains which is determined by the surface charge of clay mineral inversely affected the adsorption of both solutes.     

Adsorption of water vapor on modified activated carbons

Summary The adsorption isotherms of water vapor on modified activated carbons are measured in order to study the role of various surface groups in the primary adsorption of water molecules on these adsorbents. These adsorption isotherms are analysed by means of the Dubinin-Serpinsky and Jovanovic equations, which take into account the special features of water vapor adsorption on microporous activated carbons. Numerical analysis of the measured adsorption isotherms by means of the above mentioned equations showed their limited applicability for interpreting adsorption mechanism of water molecules on activated carbons.

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Adsorption von Wasserdampf auf modifizierter Aktivkohle

Zusammenfassung Die Adsorptionsisothermen von Wasserdampf auf modifizierter Aktivkohle wurden gemessen, um die Rolle verschiedener Oberflächentypen auf die Primäradsorption von Wassermolekülen auf diesen Adsorbenzien zu untersuchen. Die Adsorptionsisothermen wurden mittels der Dubinin-Serpinsky- und Jovanovic-Gleichungen analysiert, welche die speziellen Eigenheiten von Wasser auf mikroporöser Aktivkohle berücksichtigen. Die numerische Analyse der gemessenen Adsorptionsisothermen mittles der genannten Gleichungen zeigte ihre limitierte Anwendbarkeit zur Interpretation von Adsorptionsmechanismen von Wassermolekülen auf modifizierter Aktivkohle.

     

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.

     

Competitive adsorption from multicomponent non-electrolytic liquid mixtures on heterogeneous solid surfaces

Summary A simple model for competitive adsorption from multicomponent non-electrolytic liquid mixtures on energetically heterogeneous solid surfaces is discussed in terms of statistical thermodynamics. Integral equations are derived for the fundamental thermodynamic quantities that characterize competitive adsorption at the liquid-solid interface. Extensive model studies are presented in order to illustrate the influence of adsorbent heterogeneity on the behaviour of these thermodynamic quantities.on leave from Faculty of Chemistry, M. Curie-Sklodowska University, PL-20031 Lublin, Poland     

4A沸石从水溶液中吸附氯化十四烷基吡啶

4A沸石可部分或全部代替三聚磷酸钠,以减少合成洗涤剂对水质富营养化的影响,在硬水中使用也不致降低洗涤效力.本文研究了4A沸石在不同pH水溶液中和无机盐存在下对氯化十四烷基吡啶(TPC)的吸附作用,初步探讨了吸附机制.     

Molecular-level functionalization of electrode surfaces. An overview

Electrochemical reactions occur at electrode/electrolyte interfaces. Hence, manipulation and design of electrochemical interfaces accompanied by surface modifications have assumed vital importance. Molecular level modification, either at the monolayer or multilayer level of electrode surfaces and leading to functionalization of electrodes, is being actively pursued by researchers. Modification based on the self-assembled monolayer approach has enabled electrodes to acquire molecular recognition and molecular electronic characteristics. Functionalization of electrode surfaces using polymeric materials and enzymes has facilitated electrodes in exhibiting properties like catalysis, molecular recognition, electrochromism and birefringence. The results of such molecular level functionalization studies of electrode surfaces carried out recently in our laboratories are presented in this overview. Besides, some representative results reported from elsewhere are also included.     

高分子表面活性剂在固/液界面上的吸附形态

采用紫外光谱、XPS研究了羧甲基纤维素型高分子表面活性剂在硅胶 /水界面上的吸附形态 ,结果表明随着高分子表面活性剂溶液浓度增大 ,分子在硅胶表面的吸附由单层逐渐变为多层 ,生成半胶束结构 .     

CMC型高分子表面活性剂在固/液界面上的吸附

在润湿、乳化、洗涤、分散等应用领域中,表面活性剂分子在界面上的吸附状态对性能有重要影响.另一方面,在化学驱油过程中,表面活性剂分子在氧化物矿物上的吸附是引起表面活性剂损失的主要原因,表面活性剂的损耗量大,将降低采收率及经济效益[1].高分子表面活性剂作为一种多功能的新型表面活性剂在许多领域有广阔的应用前景,但对其性能研究尚处于起步阶段,特别是结构复杂的高分子双亲性共聚物,在吸附、乳化等方面研究尚少报导.羧甲基纤维素系列高分子表面活性剂是采用独特的超声波辐照技术合成的嵌段型共聚物,具有优良的表/界面活性[2],可望用…     

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.

     

十四烷基芳基磺酸盐在大庆油砂上的吸附性能

利用静态吸附实验研究了实验室自制的三种高纯度十四烷基芳基磺酸盐在大庆油砂上的吸附规律,并考察了吸附时间,吸附温度及磺酸盐、NaCl、NaOH、正丁醇的浓度对吸附量的影响.结果表明:吸附量随着磺酸盐浓度的增大逐渐增加后趋于平稳,随着吸附温度和正丁醇体积浓度的降低、NaCl 和NaOH浓度的增加而增大; 磺酸盐活性剂的三种同分异构体中,随两部分碳链长度趋于均等,吸附量下降,且受助剂的影响变小.吸附热力学研究表明,十四烷基芳基磺酸盐在油砂上的吸附等温线服从Langmuir 等温方程,并且计算得到的各参数均能很好地反映磺酸盐在油砂上的吸附特征.吸附动力学研究表明,Elovich 方程能够更好地描述吸附量随时间的变化情况.     

Adsorption of water vapor on a non-porous carbon surface and evaluation of the mesopore surfaces of active carbons

Adsorption of water vapor on non-porous carbon adsorbents (blacks) with different specific surfaces and a sufficiently high concentration of primary centers was studied. The maximum value of the adsorption is proportional to the surface and corresponds to the formation of (1.7±0.3) dense monomolecular layers. A method was proposed for determining the surface of non-porous carbon adsorbents and for evaluating the mesopore surfaces of active carbons.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2048–2051, December, 1993.This work was supported by the Russian Foundation for Basic Research (Grant 93-035635).     

Adsorption of bovine serum albumin at solid/aqueous interfaces

Adsorption of soluble serum proteins on hydrophilic and hydrophobic solid surfaces is important for biomaterials and chromatographic separations of proteins. The adsorption of bovine serum albumin (BSA) from aqueous solutions was studied with in situ ATR-IR spectroscopy, and with ex situ ATR-IR, ellipsometry, and water wettablity measurements. The results were used to quantitatively determine the adsorbed film thickness and surface density of BSA on hydrophilic silicon oxide/silicon surfaces, and on these surfaces covered with a hydrophobic lipid monolayer of dipalmitoylphosphatidylcholine (DPPC). The water contact angles were 5° for silicon oxide, 47° ± 1° for the DDPC monolayer, and 53° ± 1° for the BSA monolayers. At 25 °C, and with 0.01–1 wt% BSA in water, the surface densities range from Γ = 2.6–5.0 mg/m², and the film thicknesses range from d = 2.0–3.8 nm, on the assumption that the film is as dense as bulk protein. These results, and certain changes in the IR amide I and II bands of the protein, indicate that the protein adsorbs as a side-on monolayer, with some flattening due to unfolding or denaturation. The estimated -helical content for protein in buffer solutions is 15% higher than for solutions in water. The adsorption density reaches a steady-state value within 10 min for the lowest concentration, but does not appear to reach a steady-state value after 3 h f‘or the higher concentrations. Adsorption of BSA on a silicon oxide surface covered with a monolayer of DPPC leads to an adsorbed protein film of about half the thickness and surface density than on silicon oxide, but the same contact angle, indicating more protein unfolding on the hydrophobic than on the hydrophilic surface.     

Adsorption of hexyl-alpha,omega-bis(dodecyldimethylammonium bromide) gemini surfactant on silica and its effect on wettability

The adsorption of hexyl-alpha,omega-bis(dodecyldimethylammonium bromide) (C(12)C(6)C(12)Br(2)) gemini surfactant on silica and its effect on wettability have been studied. The structure of the adsorbed aggregates experiences an evolving course with the increase of C(12)C(6)C(12)Br(2) concentration. It is from no aggregates to circular islands, then to semicontinuous islands, and at last to the two-bilayer structure. No matter what kind of aggregates are in existence, their thickness values are to be the same 3.3+/-0.3 nm. The fraction of silica surface covered by the surfactant aggregates also varies from nearly zero at 0.05 mM to approximately 0.92 at 5.0 mM. The variation of contact angle against C(12)C(6)C(12)Br(2) concentration shows two distinct regions. The upward shift indicates that the surfactant molecules are adsorbed with their hydrophobic tails facing air upon increasing concentration, while the downward shift reveals that the surfactant aggregates are in existence with the hydrophilic headgroups facing air. IR spectra suggest that two different courses are involved with the increase of the surfactant concentration. One possible course is that the surfactant tails pack more closely and orderly, and the other may be that the spacer changes from stretched profile to bended conformation upon increasing the surfactant concentration.     

Strong effect of minor impurities in a gas on the rate of evaporation of solid surfaces

Evaporation of surfaces of quartz, corundum, and germanium monoxide precipitates in a flow of nitrogen and air was studied by the method of molecular nuclei of condensation, which makes it possible to determine extremely low concentrations of molecules from 10² to 10⁸ per I cm³ of a gas. The appreciable effect of low concentrations of gas impurities on the rate of evaporation of solid surfaces was found and studied in the region of low evaporation rates. Equations describing the dissimilar effects of the retention of molecules of impurities on the surface on the rates of evaporation and reverse condensation were proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 808–813, April, 1996.     

Microcalorimetric determination of displacement adsorption enthalpies of protein refolding on a moderately hydrophobic surface at 308 K

Both microcalorimetric determination of displacement adsorption enthalpies ΔH and measurement of adsorbed amounts of guanidine – denatured lysozyme (Lys) refolding on the surface of hydrophobic interaction chromatography (HIC) packings at 308 K were carried out and compared with that at 298 K. Study shows that both temperature and concentration of guanidine hydrochloride (GuHCl) affect the molecular mechanism of hydrophobic interaction of protein with adsorbent based on the analysis of dividing ΔH values into three kinds of enthalpy fractions. The adsorption in higher concentrations of GuHCl (>1.3 mol L^–1) at 308 K is an enthalpy-driving process, and the adsorption under other GuHCl concentrations is an entropy-driving process. The fact that the Lys denatured by 1.8 mol L^–1 GuHCl forms a relatively stable intermediate state under the studied conditions will not be changed by temperature.     

Adsorption of cobalt species on the interface, which is developed between aqueous solution and metal oxides used for the preparation of supported catalysts: a critical review

In the present review article, we present the efforts done so far for elucidating the mechanism of adsorption of the Co(II) species, mainly Co(H₂O)₆²⁺, on the interfacial region developed between metal oxide particles, used as catalytic supports, and aqueous electrolytic solutions. Specifically, we present: (i) the principal modes of deposition of the transition metal ionic species (TMIS) on the surface of oxidic supports related with the various methodologies used for the preparation of the supported catalysts; (ii) the state of the art concerning the general aspects of the adsorption mechanisms of the TMIS on the aforementioned interfacial region; and (iii) the works reported so far dealing with the adsorption of the Co(II) species on the surface of γ-Al₂O₃ (γ-alumina), -Al₂O₃ (-alumina), TiO₂ (rutile), and SiO₂ (silica).

It was concluded that the mechanism of adsorption depends on two main factors: on the Co(II) surface concentration and on the nature of the support surface. It seems that, generally, the mechanism changes progressively along the Co(II) surface concentration from the deposition of monodentate–mononuclear inner sphere complexes, weakly evidenced in too low values of the Co(II) surface concentration, to multidentate, multinuclear inner sphere surface complexes at relatively low Co(II) surface concentrations, and then into surface Co(OH)₂-like, eventually mixed precipitates, at relatively high Co(II) surface concentrations but at pH values lower than those required for bulk precipitation. In all cases, Co(II) forms surface species with Co(II) in octahedral symmetry.

However, the exact Co(II) surface concentration values, in which the abovementioned two transitions (concerning the deposited phase) take place, depends on the kind of the support. Thus, SiO₂ favors the formation of the Co(OH)₂-like precipitates even at relatively low Co(II) surface concentrations. In contrast, TiO₂ favors the formation of mononuclear or oligonuclear surface complexes. Finally, alumina, which exhibits the maximum adsorption capacity, favors the formation of highly defected Co(OH)₂-like precipitates, probably mixed Co–Al precipitates.

The exact local structure of the inner sphere Co(II) surface complexes, formed by exchanging the H₂O ligands with surface oxygens, has been already approached but only for the surface planes of the -Al₂O₃ and rutile monocrystals. This structure remains up to now rather unclear for the polycrystalline oxides used as catalytic supports.     

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.