Showing papers on "Langmuir published in 1972"

Cadmium adsorption maxima of soils as measured by the langmuir isotherm

Abstract: Thirty surface soils were equilibrated with four cadmium chloride solutions in a study of cadmium adsorption by soils. The data fitted the Langmuir isotherm. Where the amount adsorbed by the soil is x/m and the solution concentration at equilibrium is C, simple correlation coefficients, relating four pairs of and C for each soil, averaged 0.993. Adsorption maxima for all soils were similar in magnitude and correlated with aluminum and zinc soluble in 0.01 M CaCl2. The coefficients related to the bonding energy generally decreased in the order: organic > heavy clay > sandy and silt loam > sandy soils, and were correlated with total aluminum and iron. From a set of 13 soil properties, linear regression equations to predict the Langmuir parameters included only those variables that contributed significantly.

Sorption of light paraffins in type-A zeolites. Analysis and interpretation of equilibrium isotherms

Abstract: Equilibrium data for the sorption of light paraffins in 4A and 5A zeolites are interpreted in terms of a simple idealized model isotherm. Henry's law constants and isosteric heats of sorption, calculated from the model, agree well with published experimental values and (for CH4) with the values calculated theoretically. The observed increase in the isosteric heat of sorption with sorbate concentration arises primarily from the effect of sorbate-sorbate repulsion (finite size of sorbate molecules) and, for the systems considered, the effect of sorbate-sorbate attraction is relatively minor. Entropies of sorption are calculated and compared with the values for ideal Langmuir adsorption and the limitations of the Langmuir plot as a method of extracting Henry's law constants and saturation concentrations from experimental equilibrium data are discussed.

Cesium Adsorption on W: Ellipsometry, Auger Spectroscopy, and Surface Potential Difference Studies

Abstract: A study has been made of cesium adsorption of W and Ti using the combined measurements of ellipsometry, Auger spectroscopy, and surface potential difference measurements. The single and polycrystals of W have been cleaned in ultrahigh vacuum (∼2×10−10 Torr) and the cesium deposited as an ion beam at low voltages (5–30 V). The deposition of Cs+ did not occur unless some oxygen was detected on the sample by Auger spectroscopy. The sticking coefficient for Cs/W proved to be directly proportional to the concentration of oxygen on the W in the range 0–0.1 fraction of a monolayer oxygen coverage. The optical constants of bulk Cs can be used to interpret ellipsometric results for the adsorption of Cs on W and Ti in the region above, at and below monolayer coverage. The coverage obtained for the work‐function minimum is consistent with earlier work by Taylor and Langmuir.

Detection of Metal Ions in Stearic Acid Monolayers

Abstract: THE effect of very low concentrations of metal ions in the aqueous subphase in monolayer deposition experiments has been known for some time1,2. Langmuir and Schaefer2, in particular, noted that monolayer properties are sometimes sensitive to metal ion concentrations as low as 10-8 M and pointed out that copper and zinc ions from the dissolution of a brass trough coated with paraffin could be found in the aqueous phase.

The Effect of Heat Treatment of Silica Gels on the Calorimetric Heats of Adsorption of Sulfur Dioxide up to One-twentieth Monolayer Coverage at 423 °K

Abstract: Calorimetric heats of adsorption of sulfur dioxide have been determined at 423°K for a series of silica gels heat-treated at 240, 550, 700, 800, and 900 °C. At the lowest surface coverage of 0.01 μmol m−2, heats of 25 to 30 kcal mol−1 were observed. These values dropped rapidly with increasing coverage and approached "limiting" values of 6 to 7 and 12 kcal mol−1 for dehydroxylated and hydroxylated surfaces, respectively. To explain the results at lowest coverages an adsorbed complex involving multiple hydrogen bonds is proposed while at higher coverages it is suggested that single and dual site adsorbed species predominate for the dehydroxylated and hydroxylated surfaces, respectively. Sulfur dioxide adsorption isotherms on all gels at 423 °K obeyed the Langmuir equation.Adsorbents were characterized by nitrogen adsorption–desorption isotherms at 77 °K and pore size distribution data were calculated from the desorption branch.

Sorption from Aqueous Solution by Organo-Clays: II. Thermodynamics of 2,4-D Sorption by Various Organo-Clays

Abstract: Sorption of 2,4-D was done using water solutions and Bentone 24, an organo-clay consisting of Wyoming bentonite with one symmetry (one cation exchange capacity) of dimethylbenzyl octadecylammonium chloride sorbed to it. This coating was estimated by calculations to form nearly a complete coverage of all ionic sorption sites of the clay. Also various other organoclays were used some. These consisted of sorbed benzyl and aliphatic amines to the same bentonite clay and using the same equivalence of amine. Sorption isotherms illustrate the commonly observed condition of reduced sorption as temperature is increased, except at temperatures below 20° C. With only the one isotherm of 4.5°C. run, it is difficult to make extensive conclusions concerning this observed temperature-sorption reversal. Plotted isotherms seemed to fit Temkin, although Langmuir plots fit fairly well for most. Only organo-clays formed using an organic amine having both an aromatic and long aliphatic component had high sorption (90...

Dispersion of Iron Oxide Powder in Sodium Pyrophosphate Solutiont

Abstract: The state of dispersion and the electrochemical properties of iron oxide-sodium pyrophosphate solution system were studied. A commercial iron oxide powder prepared by calcination of FeSO4.7H20, (BET surface area, 7.55 m2/g; hematite structure) was used in this study. The pH of zero point of surface charge (ZPC) obtained from pH titration (Fig.2) was 7.9. At this pH, iron oxide was most poorly dispersed in medium (water). In Na4P2O7 solution, the degree of dispersion generally increased with the increase of the concentration of solute, and complete dispersion was observed at the concentration of 4 x 10-4mol/l. In acidic medium containing Na4P4o7, however, the suspension was found to flocculate. For instance, the flocculated concentration at pH=4.0 was (0.38-1.88) x 10-4 mol/l. The adsorption of Na4P2o7 on α-Fe2O3 (at 25°C) followed Langmuir's isotherm. The mono-layer capacity varied with the pH of media, from 14.15 x 10-7 mol/m2 at pH=4.0 to 5.34 x 10-7 mol/m2 at pH=9.5. These results suggest that sodium pyrophosphate ions are adsorbed only on positively charged sites of a-Fe2O3 surfaces. The mechanism of dispersion is proposed as shown by a schematic illustration in Fig. 12. It was concluded that the degree of dispersion depended on the net charge of surface which was determined by both the pH of media and the adsorption of sodium pyrophosphate ions on a-Fe2O3 surfaces.

Wettability of layers of polydimethylsiloxanes, transferred to glass by the langmuir method and produced by adsorption from solution

Abstract: 1. The wettability of water by layers of polydimethylsiloxanes (PDMS) transferred from the surface of water to glass by the Langmuir method, was studied. The waterproofing action of layers of PDMS increases as their thickness is increased, reaching a maximum value corresponding to the waterproofing of the volume phase of PDMS at a thickness of 2500 A in the case of the polymer with mol. wt. 1,250,000. 2. The wettability by water of layers of PDMS on glass, produced by adsorption from solutions in n-hexane, was investigated. With increasing concentration of the solutions, the contact angle of wetting of water on the adsorption layers is increased similarly to the contact angles on layers transferred from the surface of water. 3. With increasing film thickness, the values of the critical surface tension of films of PDMS approach the values for the volume phase of the polymer. 4. A conclusion on the closeness of the conformational conversions undergone by the PDMS macromolecules during the formation of a layer on a liquid substrate and in the case of adsorption from solution on a solid surface was drawn on the basis of the experimental data.