Showing papers on "Langmuir published in 1991"
TL;DR: In this article, the authors measured the adsorption of aromatic hydrocarbons from water by organo-clays and found that the planar surfaces of the compounds adsorb directly to the clay surface.
Abstract: The nature of the siloxane surface in smectites was investigated by measuring the adsorption of aromatic hydrocarbons from water by organo-clays. The organo-clays were prepared by replacing the hydrophilic, inorganic exchange cations of a series of smectites with the small, hydrophobic organic cation, trimethylphenylammonium (TMPA). Smectites with a range in charge densities were used that resulted in different TMPA contents in the organo-clays. Adsorption isotherms of benzene, alkylbenzenes, and naphthalene from water by the TMPA-smectites indicated that sorption was inversely related to TMPA content. The Langmuir form of the isotherms suggests that the aromatic compounds adsorb to the clay surface. Possible adsorptive sites in TMPA-smectites are limited to the TMPA cations and the siloxane oxygen surfaces. Because sorption increased as layer charge and TMPA content decreased, the organic compounds must adsorb to the siloxane surfaces. Calculations based on an adsorbed compound monolayer, which was estimated by fitting adsorption data to the Langmuir equation, and the N2 specific surface area of each TMPA-clay, indicate that the surface area occupied by each adsorbed molecule increases as the planar area of the molecule increases. This strongly indicates that the planar surfaces of the compounds adsorb directly to the clay surface. Apparently, the TMPA cations function to keep the smectite interlayers open. Interactions between the phenyl groups of TMPA cations on opposing interlayer clay surfaces may act to increase the size of the adsorptive regions. These results show that the siloxane surfaces of smectites can effectively adsorb aromatic hydrocarbons from water if the hydrophilic, inorganic exchange cations are replaced with small, hydrophobic organic cations. The strong adsorption of hydrophobic organic molecules from water demonstrates the hydrophobicity of the siloxane surfaces in smectites.
340 citations
TL;DR: In this article, a general isotherm equation for the first and second steps of surfactant adsorption has been derived for both aqueous and non-polar solvents.
196 citations
TL;DR: In this article, surface titrations on albite indicate that the concentration of specific surface species as a function of solution pH can be correlated to previously published kinetic data for albite dissolution.
177 citations
170 citations
TL;DR: In this paper, the P sorption characteristics of 97 soils that are representative of the agricultural areas of Western Australia were described using Langmuir and Freundlich equations using stepwise regression analysis.
Abstract: The P sorption characteristics of 97 soils that are representative of the agricultural areas of Western Australia were described using Langmuir and Freundlich equations. The Langmuir P maximum (xm) ranged from 11 to 2132 µg g-1 soil and the Freundlich k coefficient ranged from 1 to 1681. Clay content, DCB Fe and Al, oxalate Fe and AL, and pyrophosphate Al were positively related to xm and k. By using stepwise regression analysis, the combination of DCB and oxalate-soluble A1 predicted more than 75% Of the variation in the P sorption coefficients. Reactive Al compounds may thus be responsible for much of the P sorption by these soils. Soil pH in 1 M NaF (pH 8.2), which is normally used for the detection of allophanic material, was strongly related to the P sorption coefficients and might therefore be used as a quick test for predicting the P sorption capacity of soils.
142 citations
106 citations
TL;DR: In this article, the authors investigated the effect of low temperature and high pH on the removal of nickel (II) by adsorption on China clay, a cheap clay mineral, and found that a maximum removal rate of 75.3% was obtained at 50 mg L 1 metal concentration and a pH of 6.5 at 30°C.
Abstract: Adsorption of Ni(II) from its aqueous solutions on China clay, a cheap clay mineral, has been found quite favourable; a maximum removal of 75.3% was obtained at 50 mg L‐1 metal concentration and a pH of 6.5 at 30°C. Dynamic modelling of the nickel uptake has been worked out and found to be of the first order. The rate constant was found to be 9.21 x 10‐1 min‐1 under the above optimum conditions of the experiment. Coefficients of the mass transfer and intraparticle diffusion were also evaluated and found to be 2.8 x 10‐2 cm s‐1 and 4.50 x 10‐2 cm2 s‐1 respectively. Langmuir's model was used for the equilibrium modelling and the constants were calculated at 30, 40 and 50°C. Thermodynamic study at different temperatures was undertaken and the values of change in the standard free energy (?G°), enthalpy (?H°) and entropy (?S°) are reported. Low temperature and high pH favour the removal of nickel (II) by adsorption on China clay.
72 citations
TL;DR: In this paper, an equilibrium isotherm for the adsorption of ethylene, propane, propylene, and carbon dioxide on 13X zeolite has been obtained at 279, 293, and 308 K, in the pressure range 0-100 kPa.
Abstract: Equilibrium isotherms for the adsorption of ethylene, propane, propylene, and carbon dioxide on 13X zeolite have been obtained at 279, 293, and 308 K, in the pressure range 0-100 kPa. Experimental data were fitted to Langmuir, Prausnitz, and BET equations, showing the best results with Prausnitz isotherm
66 citations
TL;DR: In this paper, the adsorption of methylene blue, a cationic organic dyestuff commonly used for tracer studies in water research, on activated carbon is described.
Abstract: This investigation describes the adsorption of methylene blue, a cationic organic dyestuff commonly used for tracer studies in water research, on activated carbon.
64 citations
TL;DR: In this paper, it was found that sorption occurs by an ion exchange reaction between strontium ions in solution and calcium ions in apatite, which can be very well fitted with Langmuir's adsorption isotherm.
Abstract: Adsorption of strontium ions on synthetic hydroxyapatite was examined using both batch and column methods. The apatite was prepared from aqueous solutions and characterized by standard analytical methods. The sample obtained had characteristics of well crystallized stoichiometric hydroxyapatite. The experimental data for sorption of strontium can be very well fitted with Langmuir's adsorption isotherm. It was found that sorption occurs by an ion exchange reaction between strontium ions in solution and calcium ions in apatite.
60 citations
TL;DR: In this article, the maximum amount of Al that can be substituted for Si in the tobermorite structure is 15 to 20 mol%, and powder X-ray diffraction and cation exchange studies corroborate the above finding.
Abstract: 27Al and 29Si magic angle spinning nuclear magnetic resonance spectroscopy revealed that the maximum amount of Al that can be substituted for Si in the tobermorite structure is 15 to 20 mol%. Powder X-ray diffraction and cation exchange studies corroborate the above finding. Anomalous tobermorite structures resulted in all cases, and hydrogarnet appeared beyond the 15 to 20 mol% Al substitution limit for Si. The sorption of water molecules by synthetic [Al3++ Na+]-substituted tobermorites and their cation-exchanged forms heated at 200°C under vacuum (≥10−3 torr) was measured at 25°C in order to probe the nature of the ion-exchange cavity. Samples with ≤30 mol% of Al substitution for Si showed isotherms of Brunauer, Demming, Demming, Teller (BDDT) type I and gave better linearity with the Langmuir plot than with the BET plot. Samples with ≥35 mol% of Al substitution for Si showed BDDT type II isotherms and gave better linearity with the BET than with the Langmuir equation. The Langmuir monolayer capacity was found to depend on the Al content and on the cationic form. The Li+- and Na+-exchanged tobermorites with about 20 mol% of Al substitution for Si showed the highest Langmuir monolayer water sorption capacity. The Cs+-exchanged tobermorites showed a smaller capacity than the Li+- or Na+-exchanged samples, which can be ascribed to clogging of the ion-exchange cavity by the large Cs+ ions.
TL;DR: In this paper, a gold microband electrode was used to investigate the dynamics of lateral diffusion processes in Langmuir monolayers at the air/water interface, which can be positioned in the plane of the water surface and function as a 1D electrode in contact with a 2D collection of electroactive, water insoluble molecules.
Abstract: A new electrochemical method is described to investigate the dynamics of lateral diffusion processes in Langmuir monolayers at the air/water interface. The key element of this technique is a gold microband electrode, which can be positioned in the plane of the water surface and which functions as a 1D electrode in contact with a 2D collection of electroactive, water insoluble molecules
TL;DR: In this paper, the N-benzoyl derivatives of D- and L-phenyl alanine in water/propanol solutions were determined on a chiral-selective stationary phase, bovine serum albumin immobilized on silica.
Abstract: Equilibrium adsorption data for the N-benzoyl derivatives of D- and L-phenyl alanine in water/propanol solutions have been determined on a chiral-selective stationary phase, bovine serum albumin immobilized on silica. These data are well accounted for by an isotherm equation resulting from the sum of two Langmuir terms. The first term corresponds to the chiral-selective interactions, and the second to the nonselective molecular interactions between the enantiomers and the stationary phase. The individual band profiles of the two enantiomeric amino acids, either pure or in binary mixtures of various compositions, are predicted exactly by an equilibrium dispersive model using this bi-Langmuir isotherm. A classical Langmuir isotherm fails to predict these band profiles, illustrating the importance to collect accurate adsorption data and to use a correct isotherm model when calculating chromatographic band profiles.
TL;DR: In this paper, a theoretical model comprising the processes of micropore, macropore and surface diffusion was derived and applied to the dynamics of adsorption of CO2 on a single activated-carbon particle.
Abstract: A theoretical model comprising the processes of micropore, macropore and surface diffusion was derived and applied to the dynamics of adsorption of CO2 on a single activated-carbon particle. The effects of a nonlinear isotherm (Langmuir), particle nonisothermality and concentration dependence of the surface diffusivity were also incorporated. The theoretical model was fitted to a preliminary set of adsorption experimental data (two particle sizes, and various temperatures and concentrations) to determine the diffusion coefficients. The validity of the theoretical model was checked by using the model, with fitted diffusivities, to simulate dynamic adsorption curves at conditions different from those of the preliminary fitting data set. These model simulations were found to predict the experimental data in a satisfactory manner.
TL;DR: In this article, the results confirmed in an unambiguous way that the reaction was two-step, with one step, identified as adsorption, being first order with respect to oxygen concentration, and the other step, for desorption being zero order.
Abstract: The Langmuir adsorption isother has been tested for application to the carbon-oxygen reaction at atmospheric pressure against unique experimental data reported by Davis and Hottel in 1934; and values of activation energy and frequency factor have been obtained for both the adsorption and the desorption steps with E values of 10.04 and 32.95 kcal/mol, respectively. These values are within the expected ranges for the two steps. The evaluation required the solution of the four one-dimensional simultaneous diffusion equations for O 2 , N 2 , CO 2 with Stefan flow, to test the accuracy of the diffusion theory by comparision with experiment. Neglect of the Stefan flow is shown to result in a systematic 12% error in calculation. For the solutions to be tractable in conjunction with the reactivity equations they required linearization. The linearized equations were used to calculate the oxygen concentration at the surface of the reacting carbon samples, and the data obtained were used to validate the functional form of the Langmuir rate equation. The results confirmed in an unambiguous way that the reaction was two step, with one step, identified as adsorption, being first order with respect to oxygen concentration, and the other step, for desorption, being zero order
TL;DR: The sorption of lead by three soils that differed in texture and calcium carbonate content was studied at three different temperatures and lead sorption was found to conform to both Freundlich and Langmuir isotherms.
TL;DR: In this article, an adorption isotherm for deuterium on the nuclear grade graphitic Matrix A3-3 was measured by using a volumetric method at 1173 K at pressures < 130 Pa.
TL;DR: In this article, a new equilibrium model incorporating surface electrochemical and thermodynamic features is presented, where the Stern-Gouy-Chapman equations are used, along with a modified Langmuir isotherm in which ion activities in the mixed surface monolayer instead of concentrations are employed.
Abstract: Dissociation of protons from fatty acid Langmuir monolayers causes competitive adsorption of other counterions and partial charge neutralization. A new equilibrium model incorporating surface electrochemical and thermodynamic features is presented. The Stern–Gouy–Chapman equations are used, along with a modified Langmuir isotherm in which ion activities in the mixed surface monolayer instead of concentrations are employed. A two‐dimensional lattice model with Flory–Huggins interaction parameters χij is invoked to obtain the activities of the ions in the monolayer. The competitive adsorption of ions to fatty acid monolayers is either ‘‘ideal’’ (χij=0), or nonideal, depending on the ions mixing behavior with protons. Previous electrochemical models apply only for ideal adsorption, which appears to occur for Cd2+ and Ca2+. The nonideal adsorption is characterized successfully by the use of the above interaction parameters. Ba2+ ions show negative deviations from ideal adsorption, i.e., they adsorb less than ...
TL;DR: In this paper, the performance of polyacrylamide (PAA) on gold, and mild steel from sulphuric and hydrochloridic acid was studied using cyclic voltammetry with simultaneous monitoring of the double layer capacity.
15 Oct 1991
TL;DR: In this paper, the exact and approximate solutions of the adsorption integral equation are presented and the accuracy and resolution of truncated approximations are discussed, and the influence of experimental temperature on calculated results is also considered.
Abstract: The local exact and approximate solutions of the adsorption integral equation are presented. The Langmuir-like adsorption isotherm is assumed as a kernel. The exact local solution is compared with Sips' method. The accuracy and resolution of truncated approximations are discussed. The influence of experimental temperature on calculated results is also considered. Lateral interactions are taken into account for the random topography model of the adsorption sites.
TL;DR: In this paper, the authors determined the shape of ordered domains in a Langmuir monolayer when the amphiphilic molecules carry electric dipoles oriented in the same direction.
Abstract: We determine the shape of ordered domains in a Langmuir monolayer deposited on the surface of water, when the amphiphilic molecules carry electric dipoles oriented in the same direction. The screening of charges by water is taken into account. For horizontal dipoles, one can calculate the anisotropic line energy between the ordered and the disordered phase
TL;DR: In this article, the adsorption equilibrium data for adsorbates such as phenol, aniline, benzoic acid, o−cresol, and p−methoxyphenol on six grades of granular activated carbons were analyzed for their adherence to Freundlich or Langmuir adaption isotherms, and the results are discussed.
Abstract: Adsorption equilibrium studies of some aromatic organic pollutants in water with some commercially available standard grades of granular activated carbons have been carried out at 35°C. The adsorption equilibrium data for adsorbates such as phenol, aniline, benzoic acid, o−cresol, and p−methoxyphenol on six grades of granular activated carbons were analyzed for their adherence to Freundlich or Langmuir adsorption isotherms, and the results are discussed.
TL;DR: In this article, a two-dimensional mathematical model is developed for in-situ surfactant flushing of contaminants from an aquifer by means of injection and recovery wells.
Abstract: A two-dimensional mathematical model is developed for in-situ surfactant flushing of contaminants from an aquifer by means of injection and recovery wells. The model tracks both surfactant concentration and contaminant concentration, and permits the use of the Langmuir, Freundlich, BET, or other adsorption isotherms for the contaminant-soil binding. The permeability of the aquifer is assumed to be constant and isotropic, and local equilibrium is assumed between adsorbed and solubilized contaminant.
TL;DR: The linear relationship between heat evolved and the amount of phenobarbital adsorbed is consistent with the assumptions implicit in the Langmuir model.
Abstract: Activated charcoal is known to adsorb a wide variety of substances from solution, and several equations have been used to fit the resulting adsorption data. The determination of the correct model to fit phenobarbital adsorption onto activated charcoal was made using a calorimetric method. The differential heats of displacement of water by phenobarbital for four activated charcoals were determined and found to be linearly related to the amount of phenobarbital adsorbed. The activated charcoals studied had statistically similar heats of displacement. The linear relationship between heat evolved and the amount of phenobarbital adsorbed is consistent with the assumptions implicit in the Langmuir model.
TL;DR: In this article, a series of tetraneopentoxyphthalolocyanine (Ag2+, Ni2+, Zn2+ and Co2+) compounds are used in the study of Langmuir monolayers at the air/water interface.
Abstract: : A series of tetraneopentoxyphthalolocyanine (Ag2+, Ni2+, Zn2+ and Co2+) compounds are used in the study of Langmuir monolayers at the air/water interface. Isotherm measurements and absorption spectra of the standing monolayers are presented to discuss the mechanism of monolayer formation with tetraneopentoxyphthalocyanines. The MTNPc species from self-assembled domains when the coverage is less than 1 monolayer. Combing exciton coupling theory with the isotherm measurement provides a consistent representation of the orientation angle of the MTNPc units at the air/water interface.
TL;DR: In this article, the adsorption of oxygen on a polycrystalline silver surface using reflection-absorption infrared spectroscopy (RAIRS) was studied, and three distinct species of oxygen were identified using RT and IRS using isotopically labelled compounds.