Showing papers on "Langmuir published in 1987"

Copper adsorption by Rhizopus arrhizus, Cladosporium resinae and Penicillium italicum

Abstract: Copper adsorption by Rhizopus arrhizus, Cladosporium resinae and Penicillium italicum was studied using a copper-selective electrode. Copper adsorption by C. resinae and P. italicum obeyed the Freundlich and Langmuir isotherms for single-layer adsorption whereas R. arrhizus followed the BET isotherm for multi-layer adsorption. Temperature had little effect on adsorption over the range 4–25°C. Mineral acids were effective for desorption of copper from preloaded biomass, the efficiency of desorption increasing with decreasing pH. Other cations were also capable of copper desorption with zinc showing the greatest efficiency and sodium the lowest.

The chemisorption of hydrogen on the (111) and (110)‐(1×2) surfaces of iridium and platinum

Abstract: The chemisorption of hydrogen on both the Ir(111) and Pt(110)‐(1×2) surfaces has been examined under ultrahigh vacuum conditions with thermal desorption mass spectrometry, LEED, and contact potential difference measurements. No ordered adsorbate superstructures were observed on either surface at any fractional coverage and at surface temperatures from 100 to 700 K, and the (1×2) reconstruction of the Pt(110) surface was stable in all cases. Hydrogen adsorbs dissociatively on the Ir(111) surface, the adsorption reaction described by second‐order Langmuir kinetics with an initial probability of adsorption of 7×10−3. The rate parameters describing the second‐order desorption reaction of hydrogen from the Ir(111) surface are weakly dependent on coverage between fractional coverages of 0.1 and 0.3, and are given by Ed ≂12.6 kcal mol−1 and k(2)d ≂2×10−6 cm2 s−1. Beyond a fractional coverage of 0.3, however, both rate parameters decrease with increasing coverage. Hydrogen adsorbs dissociatively on the Pt(110)‐(1×2) surface into two distinct β2 and β1 adstates, and the ratio of the saturation densities of these two states, β2:β1, is 1:2. Adsorption into the higher binding energy β2 adstate is described by first‐order Langmuir kinetics with an initial probability of adsorption of 0.46, whereas adsorption into the β1 adstate is described by second‐order Langmuir kinetics with an ‘‘initial’’ probability of adsorption of 0.022. The rate parameters describing the desorption reaction of hydrogen fromthe Pt(110)‐(1×2) surface are strongly dependent on the coverage. In the coverage regime characteristic of the β2 adstate (θ≤0.32) the rate parameters are approximately symmetric about one‐half of saturation of this state. Specifically, from the values for the zero‐coverage limit of Ed ≂18 kcal mol−1 and k(2)d ≂10−4 cm2 s−1, the parameters first increase to maximum values of Ed ≂26.5 kcal mol−1 and k(2)d ≂0.3 cm2 s−1 at θ=0.15, and subsequently decrease approximately to the values for the zero‐coverage limit at θ=0.32 In the coverage regime characteristic of the β1 adstate (θ>0.32), the activation energy decreases continuously with increasing coverage from a value of Ed ≂17 kcal mol−1 at θ=0.35, whereas the preexponential factor remains essentially constant with a value of 3×10−4 cm2 s−1. The contact potential difference for hydrogen on Pt(110)‐(1×2) increases continuously with coverage to a value of 0.17 eV at θ=0.30. As the coverage increases further, however, it decreases continuously approaching a value of −0.50 eV at saturation. Probable binding states for the β2 and β1 adstates on the Pt(110)‐(1×2) surface are inferred from both the adsorption and desorption kinetics and the contact potential difference measurements. Comparisons of the results obtained on the (111) and (110)‐(1×2) surfaces of both iridium and platinum suggest strongly that local surface structure (e.g., ‘‘step’’ sites vs terrace sites) has a profound influence on the kinetics of adsorption of hydrogen on these surfaces. Surface structure apparently also has a profound influence on the desorption kinetics of hydrogen via the mediation of adatom–adatom interactions. Whereas both attractive and repulsive interactions are clearly manifest within the β2 adstates on the (110)‐(1×2) surfaces, only repulsive interactions are apparent on the (111) surfaces and for the β1 adstates on the (110)‐(1×2) surfaces.

Adsorption of Cu2+ or Hg2+ ion on resins prepared by crosslinking metal-complexed chitosans

Abstract: Crosslinking metal-complexed chitosans (metal ions=Cu(II), Cd(II), Zn(II), Ni(II), and Fe(III)) with (chloromethyl)oxirane yields resins having higher abilities to adsorb Cu2+ than a resin obtained from chitosan in the absence of metal ion. Resins from Cd(II)–chitosan complex can act as effective adsorbents for Hg2+; their Langmuir’s adsorption parameters depend on the quantity of (chloromethyl)oxirane used.

Adsorption and desorption kinetics of molecules and colloidal particles

Abstract: Kinetic aspects of adsorption determined by both bulk diffusion and surface activation barrier are analyzed theoretically for a spherical interface in contact with a finite volume of molecular or colloid solution. Rigorous transport equations for the bulk and surface phases are formulated together with general nonlinear boundary conditions which can be used for describing adsorption governed by various isotherms including those of Henry, Langmuir, Frumkin, etc. Explicit analytical results are derived by applying the Laplace transformation in the case of the ideal Henry isotherm for (i) a spherical adsorbing interface in contact with a quiescent solution of a finite or infinite extent and (ii) for a sphere surrounded by a stagnant layer of a finite thickness in contact with an infinite-sized reservoir of a well-stirred solution. Limiting short-time and long-time results as well as results derived in the special case of a plane geometry of the adsorbing surface are discussed. Using our general expressions the range of validity of equations previously known in the literature which were derived for the diffusion-controlled or surface barrier-controlled adsorption regime is estimated. In the general case of the nonlinear boundary conditions (Langmuir isotherm) an implicit numerical scheme is applied based on an “exact” solution of the set of nonlinear ordinary equations arising from the discretization of the surface kinetic equations.

Simplified model for the equilibrium adsorption of dyes from mixtures using activated carbon

Abstract: Adsorption isotherms have been determined experimentally for the single-component adsorption of three dyes, namely, Basic Red 22, Basic Yellow 21, and Basic Blue 69 onto carbon. In addition, the three possible bisolute isotherms and the one trisolute isotherm for these three dyes were determined. In each case the Langmuir, Freundlich and Jossens isotherm constants were determined and the Langmuir data were then used to correlate and predict the multicomponent isotherm data from single-component data in a simplified manner.

Retention of boron by agricultural soils from Ontario

Abstract: The retention of B by 20 agricultural soils from Ontario was investigated by equilibration of the soils with various concentrations of boric acid. The retention of B conformed to both Langmuir and Freundlich adsorption isotherms for all but one soil. Adsorption maxima were calculated for both isotherms and from simple linear regression analysis only pH was found to be significantly correlated with the calculated adsorption maxima. For soils with pH above 6.8, the Langmuir adsorption maxima were significantly correlated with organic C and water-soluble carbohydrate contents. Application of phase diagrams indicated that, under the experimental conditions employed, the solutions of some of the acidic soils were supersaturated with respect to the Ca-containing borate minerals inyoite, colemanite and nobleite and, given a number of reasonable assumptions, that at rates of B application of 3 kg ha−1, acidic soils could be supersaturated with respect to the mineral nobleite. The extent of complexation of B with ...

X-ray reflectivity of a Langmuir monolayer on water

Abstract: We built a special Langmuir through allowing the use of X-ray reflectivity Using the device we studied for the first time the density profile of a Langmuir monolayer directly on water This experiment opens new prospects in particular to measure the roughness of solid films on water subphase

Studies on system peaks in ion-pair adsorption chromatography. I: Evaluation of ion-pair adsorption constants and effects by the injection of finite analyte amounts

Abstract: Adsorption of a secondary amine, protriptyline, as phosphate ion-pair, to Nucleosil C18, was studied. Two different techniques were compared; the traditional break-through and the system peak technique. Both techniques indicated that the adsorption of the ion-pair was best fitted to a 2-site adsorption model of the Langmuir type, indicating a heterogenous solid phase surface. The reliability of the system peak technique was tested by comparing the retention volumes of the system peaks for different kind of equilibrium disturbances introduced into the system. When injecting finite amounts of analytes the system peak retention was affected by the analyte concentration, charge and hydrophobicity, keeping the eluent composition constant. The effects could qualitatively be explained in light of the developed model for the retention.

Two-site Model for Aluminum Oxide with Mass Balanced Competitive pH + Salt/Salt Dependent Reactions1

Abstract: A backtitration technique was used to collect proton isotherm data for an Al oxide, and was found to be stoichiometrically related to the cation and anion isotherm behavior. The adsorption of various ions by the Al oxide surface was modeled based on: (i) two surface sites, (ii) pH+salt-dependent reactions (H and Cl~, 2OH~, or Na and OH"), (iii) competitive salt-dependent reactions (Na or Cl~), (iv) COj(aq) pH-dependent reactions with the surface-OH groups, and (v) presence of an unknown MC1salt (0.0005 M). The total number of Al sites was 1.7 pmol mr or 3.4 tano\ m~ of total available sites. The pH of point of zero salt effect (PZSE) represented the surface condition in which the negative charges (or cation surfaces) equaled the positive charges (or anion surfaces); the cation exchange capacity (CEC) equaled the anion exchange capacity < AEC) at this value. The CEC-AEC data and proton isotherm data were stoichiometrically correlated. The pH of PZSE values ranged from 7.SO to 7.76 depending on the electrolyte concentration present, with lower values as the concentration increased. The negative shifts in the PZSE values are due to anion impurities initially present on the surface and positive shifts are due to cation impurities. Additional Index Words: cation/anion/proton isotherms, competitive reactions, equilibrium constants, mass balanced equations, PZSE, PZNC, ZPC. Schulthess, C.P., and D.L. Sparks. 1987. Two-site model for aluminum oxide with mass balanced competitive pH+salt/salt dependent reactions. Soil Sci. Soc. Am. J. 51:1136-1144. T ADSORPTION OF DISSOLVED SUBSTANCES OH a solid phase (charcoal) was accidentally discovered in 1785 by J.T. Lowitz (Figurovsky, 1973). A.L. Lavoisier (1743-1794) advanced a chemical, rather than mechanical, theory for the phenomenon of adsorption (Figurovsky, 1973). Modeling of the surface chemistry of oxides, colloids, or soils, has long been recognized by researchers as essential in optimizing crop yields, soil productivity, or the efficiency of any system requiring an interaction with a solid phase. Adsorption models were initially intended to describe gas adsorption by solids, and have been applied with some success to aqueous adsorption. The most fa1 Published with the approval of the Director of the Delaware Agric. Exp. Stn. as Miscellaneous Paper no. 1172. Contribution no. 215 of the Dep. of Plant Science, Univ. of Delaware, Newark, DE 19717-1303. Received 17 Nov. 1986. 2 University Graduate Research Fellow and Professor of Soil Chemistry, respectively. mous contribution was made by Langmuir (1918), whose equation may be easily derived for cation adsorption onto an oxide surface site. Assuming the following surface reaction

A new interpretation of plasma‐line overshoot phenomena

Abstract: The temporal evolution of Langmuir waves excited by high-power, high-frequency (HF) radio waves in the ionosphere is studied theoretically. This study is motivated by past observations made with the 450 MHz radar at Arecibo Observatory in Puerto Rico. Two kinds of nonlinear damping to the parametric decay instability are considered in the derivation of the rate equation for the spectral intensity of enhanced Langmuir waves. They are Langmuir wave cascading caused by nonlinear Landau damping and cross-field electron diffusion. The first damping process leads to the saturation of individual unstable Langmuir wave. The second process, which results from the incoherent scattering of electron orbits by the total excited Langmuir waves, yields anomalous damping that applies to each Langmuir wave. Consequently, Langmuir waves with smaller growth rates will be suppressed by those with larger growth rates. Such a mode competition process may cause the overshoot of the HF-enhanced plasma line observed with the Arecibo 430 MHz radar. Favorable agreement is obtained between theory and the Arecibo observations.

Effect of Complexation on the Adsorption of Cadmium by Activated Carbon

Abstract: The adsorption of Cd2+ in the absence and presence of two chelating agents was examined as a function of pH. Fits of the data to the Freundlich and Langmuir equations were compared as were results with Zn and Pb using four different activated carbons. In general, adsorption increased with increasing pH and was not extensive, particularly for Cd. At low cadmium to carbon ratios, EDTA appeared to enhance adsorption. With more realistic loadings, when competition for surface sites is greatest, the presence of EDTA is shown to be detrimental to the process. 1,10-Phenanthroline, the second chelating agent studied, was more effective for promoting the removal of Cd. The uncomplexed Cd and Cd-EDTA systems were best described by the simple Langmuir adsorption isotherm. The adsorption of 1,10-phenanthroline and its Cd complex were modeled using a modified form of the Langmuir equation.

X-ray optics in Langmuir-Blodgett films

Abstract: The Langmuir-Blodgett (LB) films are multilayered systems of amphiphilic molecules. These films are obtained by successive depositions of monomolecular layers onto a substrate. The molecules are first spread onto a water bath and laterally compressed into a solid-like monolayer (Langmuir film). The film is then transferred by dipping the substrate through the compressed monolayer. This technique allows the construction of numerous interesting physical systems by varying the number of layers and the chemical components.

Fundamental studies on the interaction between moisture and textiles part iv moisture sorption isotherm of polypeptide and polyamide fibers

Abstract: The interaction of water molecules with textiles was investigated by analyzing the moisture sorption isotherm in terms of thermodynamic parameters as well as the parameters of Brunauer, Emmett and Teller (B. E. T.)'s multi-layer adsorption model or Hill's multi-molecular adsorption model of water cluster formation for a series of natural polypeptide and synthetic polyamide fibers. The investigation was further proceeded by a broadline proton NMR spectroscopy to discuss the interaction more directly by molecular parameters than by the parameters basing on the physico-chemical and physical models.The following conclusions were obtained to characterize the interaction: (i) From temperature dependence of the moisture sorption isotherm, the differential heat of moisture sorption and, subsequently, the excess energy (entropy decrease relative to bulk water) were estimated for scoured wool and nylon 6 fibers as a function of relative humidity at a given temperature of 30°C, validating the concept of rather regular structure of sorbed water in the B. E. T. multi-layer adsorption model or the Hill's multi-molecular adsorption model of cluster formation. (ii) From the analysis of sorption isotherm of the polypeptide and polyamide fibers in terms of the B. E. T. parameters, nmax, the maximum number of layers below which the calculated sorption isotherm is closest but never exceeds the observed isotherm, is found to be 6 for almost every specimen tested. The molar concentration of monolayer-adsorbed water (Langmuir's adsorption) normalized by the degree of noncrystallinity, [Vm/(l-Xx)], is found to increase gradually at first and then rapidly with increase in the molar concentration of [CONH] groups in the back bone chain for a series of aliphatic nylons including a scoured silk, but excluding the scoured wool and an aromatic polyamide fiber, Kevlar 29; i.e., the denser the distribution of [CONH] groups along the back-bone chain, the greater is the water adsorptive capacity per [CONH] group. (iii) The narrow linewidth ΔHn in the broadline proton NMR spectrum exhibits a transition at a certain moisture regain at which the sorbed water changes in its nature from layered-adsorbed water with the number of layers up to nmax to less interacted water with the number of layers of n>nmax, but not to an extent of far less interaction as comparable to the water in liquid state; i.e., the so-called bulk water.

Applicability of the equations of Freundlich and Langmuir to the adsorption of the azo dye procion scarlet on paramorphic colonies of Neurospora crassa.

Abstract: Experiments on the adsorption of Procion Scarlet MX-G by normal hyphae and by paramorphic colonies of Neurospora crassa were performed at pH 2.5, 4.5 and 6.5 at 30 degrees C. The measured adsorption isotherms were evaluated by the Freundlich and Langmuir equations. The removal of dye was most effective at pH 2.5 and more dye was adsorbed per unit mass of cells in the paramorphic cultures than in the normal hyphae. The statistical tests showed Langmuir's equation to give a better fit to the adsorption data.

I. Interaction with Bentonite Clay Systems

Abstract: B. B. SITHOLE and R. D. GUY* Trace Analysis Research Centre Dept. of Chemistry, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4,11 (Received October 6, 1985; revised October 27, 1986) Abstract. The interactions of tetracycline with model clay adsorbents has been studied as a function of suspension pH, ionic strength, and adsorbate concentration. The model clay adsorbents were the Na, Ca, and dodecyltrimethylammonium forms of bentonite and a tannic acid covered bentonite. The adsorption isotherms were of the Langmuir type and the adsorption capacity decreases in the order tannic acid-clay > Ca-clay > Na-clay > dodecyltrimethylamrnonium-clay. The adsorption onto the clay substrates decreases as the ionic strength and pH increases.

Electrocatalysis under Temkin adsorption conditions

Abstract: The theoretical description of steady-state current–potential curves for simple electrocatalytic reactions under Temkin adsorption conditions has been extended beyond the potential range of quasi-equilibrium. The theory predicts that current–potential curves calculated on the basis of Langmuir and Temkin adsorption conditions exhibit only minor differences at coverages below 0.9. The volcano curve for hydrogen evolution by the Volmer–Heyrovsky reaction mechanism proves to be independent of the nature of the adsorption isotherm if plotted against the apparent free energy of adsorption at equilibrium coverage under standard conditions. For any other value of the free energy of adsorption, however, the width of the volcano curve depends on the Temkin heterogeneity factor f. The volcano curve is not truncated under Temkin adsorption conditions.

Aqueous solubility of solvent extraction reagents: a monolayer dissolution method

Abstract: ABSTRACT An experimental method, based on Langmuir film balance techniques, Is presented for determining the aqueous solubility of sparingly soluble solvent extraction reagents. According to this method, the reagent of interest is spread as a monomolecular film on a Langmuir trough and the contraction of the film area accompanying extractant dissolution is monitored as a function of time while maintaining a constant film pressure. Quantitative analysis of the diffusion-controlled film dissolution kinetics yields the extractant concentration in equilibrium with the monolayer at a specified constant surface pressure. Solubility data obtained by applying this method to dinonylnaphthalene sulfonic acid (HDNNS) and 2-hydroxy-5-nonylbenzophenone oxime (HBPO, active extractant in LIX65N) are reported.