Showing papers on "Langmuir published in 1982"

Adsorption of dyes on chitin. I. Equilibrium studies

Abstract: Equilibrium isotherms have been studied for the adsorption of four dyestuffs, namely, Acid Blue 25, Acid Blue 158, Mordant Yellow 5, and Direct Red 84, onto chitin. Langmuir and Freundlich constants have been determined and the effects of chitin particle size and solution temperature have been investigated. Theoretical isotherms have been compared with experimental data and good agreement was obtained using a composite isotherm of the general form: Ye = iCe/(1 + jCem), where i,j, and m are constants.

Gas sorption and transport in poly(phenylene oxide) and comparisons with other glassy polymers

Abstract: The sorption and transport of several gases in poly(phenylene oxide) were measured at 35°C, and the results have been analyzed in terms of the dual sorption/mobility models which have been successfully employed for this purpose for other glassy polymers. Both the extent of sorption and rate of permeation of gases are quite large for poly(phenylene oxide) compared to other glassy polymers with rigid chain backbones. It is shown that the high extent of sorption is owing to the high glass transition temperature of this polymer, but this is not a significant factor in its high permeability to gases. The latter stems from large diffusion coefficients. It is shown that the capacity of the Langmuir mode of sorption inherent to glassy polymers is related to the value of the glass transition temperature in a general way for a wide variety of polymers. Observations about the diffusion coefficients for numerous gas–polymer pairs are discussed.

Retention and Movement of Fluoride in Soils

Abstract: Displacement and retention of fluoride in soils were studied in laboratory experiments. Fluoride adsorption and desorption isotherms were determined in the range of 0 to 5000 ..mu..g mL/sup -1/ of dissolved F by shaking 1:10 soil/NaF solution suspensions. The observed relationship was nonlinear. Neither Langmuir nor Freundlich equations were unbiased predictors of the measured relationship. The experimental errors propagated in the computational analysis and made such adsorption data quite error-prone. For soils with a low F retention the confidence interval was wide, and vice-versa. In an acid clay soil an apparent adsorption equilibrium was attained within 3 h, but several days were required for the equilibration of the calcareous soils with the NaF solution. Adsorption and desorption of the calcareous soils exhibited a hysteretic behavior, but in the case of the acid soil no hysteresis was observed. The transport of F was studied by percolating soil columns at a constant flow rate. The F breakthrough depended primarily upon the F concentration in the infiltrating solution and soil type, whereas the ionic composition of the infiltrating solution had a less pronounced effect on the breakthrough behavior. The F retention within the soil columns and the adsorption estimates obtained from the isothermsmore » agreed well in the case of the acid soil, but the calcareous soils retained one-third to one-half as much F during the percolation experiment. 16 references, 8 figures, 1 table.« less

Separation of xylenes on Y zeolites. 1. Determination of the adsorption equilibrium parameters, selectivities, and mass transfer coefficients through finite bath experiments

Abstract: The adsorption of xylene isomers on completely potassium exchanged Y zeolite has been investigated. The adsorption equilibrium data for single components and mixtures have been described with the Langmuir and Fowler isotherms. The kinetics of adsorption of the different components on zeolite pellets and powder have also been studied. The obtained experimental data have been interpreted by means of a kinetic model in which the role of inter-and intraphase diffusion processes are emphasized.

The kinetics of protein adsorption on synthetics and modified natural surfaces

Abstract: The kinetics of adsorption of albumin and fibrinogen from phosphate buffered saline (pH 7.35, 280 mosmol) was studied as a function of time, temperature, and bulk protein concentration on Cuprophan (regenerated cellulose), Silastic (silicone rubber), and Shiley heart valve xenografts under static conditions. Adsorption of both proteins on the synthetics appeared to be rapid, irreversible with respect to dilution, and at surface concentrations not exceeding what would be expected for a monolayer. A diffusion-limited model, using the Smoluchowski boundary condition, was derived and was shown to demonstrate the essential characteristics of sorption on synthetics. Both proteins adsorbed to the xenograft with a reversibly bound protein fraction and an irreversibly bound fraction. The reversible fraction was modeled well by a second-order kinetic (Langmuir) process far from saturation. Energies of activation were estimated to be about 3 and 6 kcal/mole for fibrinogen and albumin, respectively. Enthalpies of adsorption were very low, 0.4 kcal/mole for fibrinogen and 1.5 for albumin. The irreversibly bound fraction was modeled well as a diffusion-limited process far from saturation.

The adsorption of organic and inorganic phosphates onto a new activated carbon adsorbent

Abstract: A study was made of the adsorption characteristics of triethyl phosphate (TEP), dimethyl phosphate (DMP), and orthophosphate (OP), from aqueous solution onto activated charcoal cloth (ACC). The isotherms obtained were of a Langmuir type and, at neutral pH, and 293°K, the equilibrium adsorption capacities were 2430, 107, and 44.6 μmol g−1 from TEP, DMP, and OP solutions, respectively. DMP and OP adsorption was found to be strongly pH dependent. It is suggested that this dependence arises because of a combination of their pK values and the charge on the charcoal cloth surface in aqueous media. The latter was established by measurement of the electrophoretic mobility as a function of pH. No pH effect was evident in the TEP adsorption. Prior to reaching equilibrium it was shown that adsorption was proportional to ( time ) 1 2 indicating a dependence on intrafibril (particle) diffusion.

The comparative significance and utility of the Freundlich and Langmuir parameters for characterizing sorption and plant availability of phosphate in soils

Abstract: In studies using 62 Australian and English soils, the two parameters of the Freundlich sorption equation were compared with phosphate sorption capacity, calculated from the Langmuir 'two-surface' equation, and sorptivity and affinity indices calculated from the simple Langmuir equation applied to an isotherm concentration range of 0-5µg phosphorus/ml. The Freundlich extensive parameter was most highly correlated with sorptivity, and to a decreasing extent with sorption capacity and affinity. It appears to be fundamentally a sorptivity index which reflects the sorption capacity more than the affinity component of sorption, although greatly underestimating sorption capacity. The reciprocal of the Freundlich exponent proved to be an affinity parameter and was most useful in this role on soils of similar sorption capacity. However, conflicting results on different groups of soils showed that this parameter was less distinctive in its role than the others. Studies on two different groups of soils showed that the sorptivity and affinity parameters from the Langmuir equation accounted for more of the variance in plant uptake of labile phosphate than the Freundlich parameters.

The Adsorption and Desorption of Zinc Di-isopropyldithiophosphate on Steel

Abstract: The adsorption of zinc di-isopropyldithiophosphate from n-hexadecane onto iron powder and onto EN31 steel disks has been studied as a function of time, temperature, and additive concentration. 65Zn and 14C radiolabelling has been used to probe aspects of adsorption behavior. The ZDDP is adsorbed onto disk surfaces but there is subsequent loss of Zinc from the adsorbed layer. Both parent ZDDP and zinc-depleted product appear to be physisorbed. A simple model based on Langmuir kinetics, and which allows for adsorption and desorption processes, gives a satisfactory representation of observed behavior. Activation parameters have been calculated. Some comments have been made on the relation between adsorption and antiwear activity. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in New Orleans, Louisiana, October 5–7, 1981

Cotton cellulose: enzyme adsorption and enzymatic hydrolysis

Abstract: Adsorption of a crude cellulase complex from Trichoderma viride on variously pretreated cotton celluloses has been studied in the framework of the Langmuir approach, in the temperature range 2–8°C. The saturation amount of adsorbed enzyme has been related to their susceptibility to hydrolysis. In every case the adsorption process was found to be faster by 2–3 orders of magnitude than the hydrolysis step to give end products. For one substrate, the Langmuir parameters were found to be fairly well correlated with the value of the Michaelis constant Km, measured for its enzymatic hydrolysis, and the adsorptive complex (ES)ad was indistinguishable from the complex (ES) of the Michaelis–Menten model for the hydrolysis.

Adsorption kinetics of nonanediol and nonane dicarbonic acid at the air/water interface

Abstract: The adsorption kinetics of nonanediol and nonanedicarbonic acid was investigated using the oscillating jet method. It was shown that for diffusion controlled adsorption kinetics, the dynamic surface tension minous the equilibrium surface tension is linear with t—1/2 at least for sufficiently long times. The adsorption rate of these products is not controlled by diffusion and the subsurface concentration is very nearly to the bulk concentration. Results are discussed by replacing the condition of local equilibrium between subsurface and surface by a kinetic equation of the Langmuir type. There from the adsorption and desorption rate constants are calculated. The ratio of this constants give the Langmuir adsorption constant, also obtainable for equilibrium data. The agreement between the Langmuir adsorption constant from thermodynamic and dynamic data seems reasonable.

The Adsorption and Desorption of Dibenzyl Disulfide and Dibenzyl Sulfide on Steel

Abstract: The adsorption of dibenzyl disulfide and dibenzyl monosulfide from hexadecane on a chromium steel has been studied as a function of time, temperature, additive concentration and stirring rate. Radioisotopic labelling with 35S and 14C has been used to elucidate aspects of the adsorption behavior. The reaction is in two stages, physical adsorption which follows Langmuir kinetics up to θ ˜ 0.9, and then chemisorption to monolayer sulfurisation. The desorption of the additive has also been studied as a function of time and temperature, from θ ˜ 0.8. Again Langmuir kinetics is observed. The enthalpy and entropy of activation for these processes have been calculated.

Adsorption of Phosphate Ion by Hydroxyapatite in Water

Abstract: The amount of phosphate ion, xp, adsorbed by synthetic hydroxyapatite (HAP) was measured under various conditions in water. A long time was required to reach adsorption equilibrium, and the adsorption process was largely irreversible with respect to concentration. The adsorption isotherm was not of Langmuir type, but was dominated by the ionic product of adsorbate, depending on the species of counter ion. The value of xp decreased with pH due to mutual electrostatic repulsion between adsorbed phosphate ions, which are deprotonated, and due to competitive adsorption between phosphate ion and OH-ion. The adsorption process was also found to be endothermic, because the adsorption increased with temperature. The adsorbate ion and adsorbent surface may be dehydrated when they are bound together. From all these results, it was concluded that the adsorbate phosphate ion is oriented and coordinated to calcium ion on the surface of HAP, and this is the reason why the adsorption of phosphate ion is irreversible.

Effects of carbon filler on sorption and diffusion of gases through rubbery materials

Abstract: Effects of carbon filler on the sorption and diffusion of carbon dioxide in natural rubber and in styrene-butadiene rubber have been studied. Sorption isotherms conform to Henry's law in unfilled rubber and to Langmuir's law in carbon black. The isotherms in filled rubber exhibit a combination of the two sorption modes. The Henry's law solubility parameter kD increases with carbon filler content; the Langmuir saturation constant C′A initially is constant with filler level, but then decreases abruptly when carbon particles begin to aggregate. The diffusion coefficient decreases with increasing filler content, presumably owing to geometric effects and to polymer chain immobilization in the interfacial regions.

Effect of LiCl on the Rate of Calcite Decomposition

Abstract: The rate of decomposition of calcite powder in vacuum was measured by the Langmuir and Knudsen methods. Measured pressures in effusion cells in the absence of additives approach the equilibrium value. The Langmuir experiments gave an apparent equilibrium CO2 pressure of =3×10−4 times the known pressure for the reaction. It is suggested that the CO2 is in equilibrium with the calcite but the CaO is not. In Langmuir experiments, 10 wt% LiCl does not increase the initial decomposition rate. In the Knudsen cells, 10 wt% LiCl can increase the initial rate by >2 times. LiCl reduces the surface area of the product CaO under either condition from ≥30 to ∼1 m2/g. Probably an LiCl-CaO eutectic provides a solution path for CaO recrystallization and, at high CO2 pressures, also for CaCO3 decomposition.

Direct measurement of adsorbed amount of sodium tetradecyl-2,3-3H,3H-sulfate at the oil-water interface by radiotracer method

Abstract: The adsorbed amount of sodium tetradecyl-2,3- 3 H, 3 H-sulfate ( 3 HSTS) at the flat interface of toluene and water was measured by the radiotracer technique. The interfacial radioactivity was detected by a plastic scintillation probe which was designed so as to be capable of being in direct contact with the oil phase. Measurements were made on the solutions of 3 HSTS without and with added sodium chloride. The correction for the background effects from the aqueous phase was made by the radioactive measurements for the sodium butyl-3,4- 3 H, 3 H-sulfate solution of the same radioactive and chemical concentrations with the 3 HSTS solution. The observed isotherms indicated a Langmuir type with a level value below the CMC of sodium tetradecyl sulfate. Adsorbed amounts at close-packed adsorption were 1.72 and 2.52 μmole m −2 for the surfactant solutions without and with sodium chloride at 30°C, respectively. The applicability of the Gibbs equation to the adsorption of ionic surfactant at the flat O/W interface is discussed. The observed isotherms coincide sufficiently with the isotherms calculated from the interfacial tension vs concentration curves by the Gibbs isotherm to confirm its applicability.

Adsorption of alkylphosphoric acid on kaolinite and smectite in water-decane

Abstract: Bis-ethyl 2-hexylphosphoric acid (di-2 EHPA) dissolved in decane is chemisorbed on kaolinite and montmorillonite dispersed in an acidic aqueous solution. The adsorption results in the formation of complexes with the surface cations of the clays. The adsorption isotherms are of the Langmuir type and reveal a limiting value of adsorption on H+-kaolinite of 12.2 mg/g, comparable to that measured in the absence of water. For H+-montmorillonite, however, the limiting value in the presence of acid is somewhat less (20.6 mg/g vs. 23.8 mg/g). Di-2 EHPA does not react with the magnesium cations available at the surface. The isotherm is “stepped” and suggests the presence of adsorption sites with distinctly differentiated energies. The sites of di-2 EHPA adsorption can be masked by treating the two clay minerals with polyphosphate anions. Thus, with pyro- and tripolyphosphate anions, di-2 EHPA uptake in acidic medium is very low. Adsorbed di-2 EHPA can be recovered by treating the clays with fluoride, hydroxyl, and dihydrogenphosphate anions. Dihydrogenphosphate anions lead, however, to a state of equilibrium between the organic and inorganic phosphate anions adsorbed.