Showing papers on "Langmuir published in 1988"

Physical Adsorption on Heterogeneous Solids

Abstract: A unified approach to physica adsorption of heterogeneous solids is presented. In the case of single-gas adsorption the overall adsorption isotherms, derived by solving the fundamental integral equation for Langmuir's local isotherm and different energy distributions, are discussed. These isotherm equations are extended for Fowler-Gugaenheim and BET local adsorption isotherms. Moreover, the overall isotherms for single-gas adsorption are generalized for mixed-gas adsorption, adsorption from solutions of non-electrolytes and multi-solute adsorption from dilute solutions. The last section of this paper is devoted to the kinetics of localized adsorption of cases, the gas and liquid mixtures on energetically heterogeneous solid surfaces.

Surface tension of binary metal—surface active solute systems under conditions relevant to welding metallurgy

Abstract: Since the fluid flow, heat transfer, and the resulting weld properties are significantly affected by interfacial tension driven flow, the variation of interfacial tension in dilute binary solutions is studied as a function of both composition and temperature. Entropy and enthalpy of adsorption of surface active components such as oxygen, sulfur, selenium, and tellurium in Fe-O, Fe-S, Fe-Se, Cu-O, Cu-S, Cu-Se, Cu-Te, Ag-O, and Sn-Te systems were calculated from the analysis of the published data on interfacial tension of these systems. For these calculations, a formalism based on the combination of Gibbs and Langmuir adsorption isotherms was used. Interfacial tensions in Cr-O, Co-S, and Ni-S systems, where the data are scarce, were predicted by using certain approximations. The computed values were found to be in reasonable agreement with the data available in the literature. Temperature coefficients of interfacial tensions were calculated for several binary systems. It was demonstrated that in dilute solutions, the temperature coefficient of interfacial tension is strongly influenced by the heat of adsorption which, in turn, is influenced by the difference in electronegativity between the solute and solvent ions.

Magnetoliposomes. Formation and structural characterization.

Abstract: The adsorption of different types of phosphatidylglycerols onto magnetizable solid particles is studied. The super-paramagnetic magnetite spheres used have an average diameter of only 14 nm and are stabilized by lauric acid to keep them in solution. During incubation and dialysis of this water-based magnetic fluid in the presence of preformed sonicated phospholipid vesicles, magnetoliposomes are formed which are captured from solution with high efficiency by high-gradient magnetophoresis. Support for the bilayer character of the phospholipid coat is derived from both theoretical calculations and experimental data. Phospholipids which form the inner monolayer are adsorbed very quickly with their charged head-group orientated towards the iron oxide surface. The high-affinity character of the binding is reflected in the adsorption isotherms and is further illustrated by their non-extractability with high concentrations of Tween 20. The outer layer assembles through interaction with the exposed hydrocarbon chains. As compared to the inner layer, the phospholipids adsorb at a much slower rate and are displaced by Tween 20 concentrations which usually disrupt conventional membranes. The adsorption isotherms for this layer obey the Langmuir expression. The affinity constants, derived from them, progressively increase as the hydrophobic nature of the phosphatidylglycerols is more pronounced.

As(III) removal from aqueous solution by adsorption

Abstract: The removal of As(III) from aqueous solutions at different concentrations, pH and temperatures by haematite has been carried out successfully. The maximum removal was found to be 96 % at concentration 13.34 μmol L−1, temperature 20 °C and pH 7.0. The process of uptake follows first-order adsorption rate expression and obeys the Langmuir's model of adsorption. The removal of As(III) by haematite is also partially diffusion controlled and mass transfer coefficients, diffusion coefficients and thermodynamic parameters have been determined to explain the results.

Adsorption of Protein by Bentonite in a Model Wine Solution

Abstract: The adsorption of bovine serum albumin by bentonite in model wine solutions was studied. The attainment of equilibrium was found to be rapid and complete within 30 seconds of the addition. The extent of adsorption was characterized using both the Langmuir and Freundlich equations. The constants and the goodness of fit were determined by linear regression of the transformed equations. The adsorption was independent of temperature but varied with protein content, pH, and ethanol content. A comparison of various types of bentonite showed that calcium bentonites had lower adsorptive capacities, even though their measured cation exchange capacities were similar. charge, or perhaps a net negative charge, may be adsorbed due to polar terminal regions which are locally positive, by chelation of other cations, or by a hydrogen-bonding mechanism; however, a strong preference for cationic protein fractions is expected. Secondary aspects which will effect the adsorption of protein fractions are the competition from other cations in the solution matrix and the solvent properties. In wines, this competition would be from potassium, cal- cium, magnesium, sodium, and hydrogen ions as simple cations, most amino acids, some peptides, and other cationic protein fractions. The solvent effect of ethanol would be to displace water molecules from the interlattice spacing of the bentonite crystal (22) and to alter the dielectric value of the solutions, thus altering protein conformations and perhaps adsorption. The role of temperature on protein adsorption by bentonite is open to question, since it has not been addressed in previous studies. Bentonite treatments are actually three distinct physical reactions -- dispersion of the agent, adsorption of the solutes, and settling of the complex -- and there is some confusion as to whether a temperature effect is related to the adsorption or to the settling phase of the treatment. The influence of protein concentration on the adsorp- tion may lead to competitive binding and poorer adsorp- tion at relatively high concentrations. This kind of effect is observed in the substrate binding of certain enzymes, but such an effect has not been observed with other fining agents.

Sorption and Sorptive Interaction of Cadmium and Zinc on Hydrous Manganese Oxide

Abstract: Adsorption of Zn, Cd, and Ca by was measured at pH 4, 6, and 8 by a batch technique at steady-state conditions. Fitting the data to Langmuir and Freundlich expressions suggested that there were two or more mechanisms or sites of sorption for both Zn and Ca. The "higher energy" site(s) (first to fill) showed preference for Cd over Zn, whereas the reverse was true for the lower energy site(s). Simultaneous addition of both Cd and Zn reduced adsorption of both ions. Cadmium and Zn adsorption diminished somewhat when Ca was present at higher Zn and Cd loadings but competition from Ca was minimal at low metal loadings. It is proposed that the high energy binding is an exchange sorption on the negatively charged oxide sites by displacement of surface and diffuse layer cations and protons, which binds Cd more strongly than Zn. On a relative basis at pH 6 and 8, Zn is more strongly bound than Cd. The higher surface charge density and greater proportion of Zn hydroxy solution phase species at higher pH may favor Zn sorption. Competition between Cd, Zn, and Ca was observed at pH 4, 6, and 8, suggesting that solution bulk precipitation was not controlling solution metal

Nucleation in two-dimensional Langmuir turbulence

Abstract: Simulations of the long-time behavior of the Zakharov model of Langmuir turbulence in two spatial dimensions reveal regimes where nucleation of localized electrostatic fields in previously burnt out density cavities is the mechanism which sustains the turbulence. Power spectrum diagnostics show that for moderate ion wave damping the Langmuir energy is carried by localized states.

β‐Carotene adsorption on acid‐activated montmorillonite

Abstract: The adsorption of β-carotene from solution in benzene on acid-activated Canakkale montmorillonite of Turkey has been investigated. The adsorption isotherm had two steps. The first step was of the Langmuir type, and the isosteric heat of adsorption corresponding to this step was equal to −193.514 kJ/mol. The decrease in the total number of acid sites of the clay surface was determined to be 0.45×10−4 mol/g clay by nonaqueous titration with diethylamine. The phenomenon seems to be mainly a chemisorption stemming from the interaction of β-carotene with acid sites. Also, the activated clay acts as an oxidation catalyst on the β-carotene left in the solution.

A contribution to the study of phosphate sorption by three Greek fly ashes

Abstract: Three fly ashes from Greece, produced from lignite burning, proved efficient in removing phosphate from solution. Maximum amounts of phosphate removed ranged from 0.064 to 0.099 mmol PO3 4 – per g of material. Fly ashes that contained higher amounts of calcite and anhydrite seemed to be better sinks for phosphate. From the various adsorption isotherm equations tested, the Langmuir equation described phosphate sorption satisfactorily. Although, the exact mechanism of phosphate sorption could not be revealed, it is believed that it involved an adsorption and/or precipitation process.

Sorption Behavior of Cesium, Strontium and Americium Ions on Clay Materials

Abstract: The sorption behavior of Cs, Sr and Am ions on loams, which is widely distributed in Tohoku district of Japan, was studied under static and flowing conditions. The measurements of ion distribution ratios, which span a range of nearly three orders of magnitude, were fitted to Freundlich or Langmuir isotherms and the sorption parameters of isotherm equations were determined. It was found that the sorption of these ions on loams is due to the ionic exchange with Na, Ca and Mg ions of the loams. Analyzing the breakthrough curve of Cs ion sorption on a loam sorbent yielded 0.2 s−1 and 0.32 em for values of the overall mass transfer coefficient and of the length of adsorption zone, respectively.

Adsorption kinetics of surfactant molecules at a liquid-air interface

Abstract: The adsorption of the surfactant sodium–dodecyl naphthalene–sulfonate from the bulk to the water–air interface was studied by optical second harmonic generation. An initial rapid Langmuir type of adsorption to about 80% of a monolayer is observed, followed by a much slower adsorption until a full monolayer is formed.

Design and Interfacing of an Automated Langmuir-Type Film Balance to an FT-IR Spectrometer

Abstract: We report the design of a surface analysis accessory that allows for the use of external reflection FT-IR spectroscopy to investigate the structure of insoluble monolayer films in situ at the air/water interface. The Langmuir film balance constructed for this purpose is optimized to contain the monolayer film at the focal point of the infrared beam, as well as to generate high surface pressures within the film. The optical interfacing of the film balance to an FT-IR spectrometer is also described. Results are presented for a representative surface pressure/molecular area isotherm and infrared spectrum for a phospholipid monolayer film.

Removal of basic dye (crystal violet) from water using wollastonite as adsorbent

Abstract: Batch mode of experiments indicate that low concentration, small particle size of adsorbent, high temperature and alkaline pH of the solution are favourable for the removal of crystal violet (Basic violet ‐ 3) from aqueous solutions by adsorption on wollastonite. The adsorption behaviour of adsorbent follows the Langmuir's isotherm. The kinetics of adsorption has been studied in the light of adherence of adsorbate molecules on the outer interface of adsorbent as well as adsorbate transport within the pores of adsorbent. The thermodynamics of the process at different temperatures indicate favourable adsorption at the solid‐solution interface. Acid‐base dissociation of the hydroxylated oxides of adsorbent and ion exchange with dye cations are the suggested reasons for the maximum removal in alkaline medium.

Phenobarbital adsorption from simulated intestinal fluid, U.S.P., and simulated gastric fluid, U.S.P., by two activated charcoals.

Abstract: Adsorption of phenobarbital from simulated intestinal and gastric fluids by two activated charcoals was studied. Adsorption isotherm data were analyzed by the linearized Langmuir equation and by nonlinear least-squares regression employing both Langmuir and Freundlich models. These analyses indicated differences in the capacities of the two charcoals for phenobarbital which could not be completely explained by surface-area considerations.

A model for gramicidin A'-phospholipid interactions in bilayers.

Abstract: A model is proposed for the effect of gramicidin A′ on the order and structure of phospholipid dispersions. According to this model, the addition of gramicidin A′ influences the surrounding lipids via two independent mechanisms. The first arises from a drop in surface pressure for those lipids substantially bounded by gramicidin A′. The second mechanism arises from the increase in the phospholipid headgroup spacing due to the small polar region of the polypeptide. The model provides an explanation for the currently available NMR, X-ray diffraction and Langmuir monolayer results. The model also suggests mechanisms for the ability of gramicidin A′ to trigger a transition of the lipid from the lamellar to hexagonal II phase, the dependence of this transition on the lipid chain length and the formation of a lamellar phase with lysophosphatidylcholine.

The flow of molecular monolayers in relation to the design of Langmuir troughs and the deposition of Langmuir-Blodgett films

Abstract: The flow of condensed molecular monolayers of barium stearate has been examined as a model system in relation to the deformation of monolayers during experimental procedures. It is shown that when a monolayer is transferred at constant area along the surface in a Langmuir trough the movement of the monolayer in relation to the boundaries sets up a circulation in the surface. This can be eliminated by a simple modification to a conventional trough. A new method is described to follow the progressive distortion of the monolayer during deposition of Langmuir-Blodgett films. This is applied to show how distortion can be minimised in a conventional Langmuir trough and to produce designs using a flexible belt to compress the monolayer. A belt profile is proposed which can be used to deposit the monolayer with minimal distortion.