Showing papers on "Langmuir published in 2000"

Adsorption of Methylene Blue from Aqueous Solution onto Perlite

Abstract: Adsorption of methylene blue from aqueous solutionsonto unexpanded and expanded perlite samples activatedby H2SO4 and NaCl solutions has beeninvestigated, to assess the possibility of usingperlite for removing cationic dyes from aqueoussolutions. The effects of pH and temperature of dyesolution on the adsorption capacities have beenevaluated. The experimental data were correlatedreasonably well by the Langmuir adsorption isothermand the isotherm parameters (Qm and K) have beencalculated. The removal efficiency (P) anddimensionless separation factor (R) have shown thatperlite can be used for removal of methylene blue fromaqueous solutions, but unexpanded perlite is more effective.

Removal of Basic Dyes (Rhodamine B and Methylene Blue) from Aqueous Solutions Using Bagasse Fly Ash

Abstract: Bagasse fly ash, a waste generated in sugar industries in India, has been converted into an inexpensive adsorbent material and utilized for the removal of two basic dyes, rhodamine B and methylene blue. Results include the effect of pH, adsorbent dose, dye concentration, and presence of surfactant on the removal of rhodamine B and methylene blue. The adsorption data have been correlated with both Langmuir and Freundlich adsorption models. Thermodynamic parameters obtained indicate the feasibility of the process, and kinetic studies provided the necessary mechanistic information of the removal process.

Palladium sorption on glutaraldehyde-crosslinked chitosan

Abstract: The high nitrogen content of chitosan is the main reason for its ability to sorb metal ions through several mechanisms including ion-exchange or chelation, depending on the metal and the pH of the solution. Glutaraldehyde is used to crosslink chitosan through imine linkage between amine groups of chitosan and aldehyde groups of the crosslinking agent. This modified biosorbent was studied for palladium recovery in acidic medium (around pH 2). The influence of several parameters such as pH and competitor anions were studied with respect to sorption equilibrium. Sorption isotherms were obtained and modeled using the Langmuir and the Freundlich model. This study also examines the effect of palladium concentration, particle size, sorbent dosage, and the extent of crosslinking on sorption kinetics. Kinetic curves are modeled using single diffusion model equations to evaluate the predominance of either external or intraparticle mass transfer resistance. The influence of the acid used to control the pH of the solution was examined in conjunction with the influence of competitor anions. Sulfuric acid proves to be unfavorable to palladium sorption, in comparison with hydrochloric acid. However, the addition of chloride anions in a palladium solution, whose pH is controlled with sulfuric acid, enhances metal anion sorption: results are interpreted with reference to chloropalladate speciation.

Colour Removal from Synthetic Dye Wastewater Using a Bioadsorbent

Abstract: Removal of dyes (Crystal Violet, Methylene Blue, Malachite Greenand Rhodamine B) from aqueous solutions at differentconcentrations, pH and temperatures by Neem sawdust has beencarried out successfully. The percentage of the dye adsorbed byNeem sawdust decreased from 91.56 to 78.94 and 84.93 to 71.25 for Crystal Violet and Malachite Green, respectively, when the concentration of the dye was increased from 6 to 12 mg L-1 at atemperature 30 ± 1 °C and pH 7.2. Adsorption ofother dyes (Methylene Blue and Rhodamine B) also decreased withincreasing concentration of the dye in solutions. The values ofthe rate constant of adsorption (kad) of Crystal Violet at25, 35 and 45 °C were found to be 10.80, 10.52 and 10.25 × 10-2 min-1, respectively. The values of the Langmuir constant for adsorption capacity (Qo) of Crystal Violet on the adsorbent varied from 4.44 to3.99 mg g-1, respectively, with the increase of temperaturebetween 25 to 45 °C. The equilibrium data followed theLangmuir model of adsorption. The variation in the extent ofremoval with pH has been explained on the basis of surfaceionisation and complexation. Thermodynamic parameters(ΔG, ΔH and ΔS) have also been determinedto explain the results.

Agricutural by-product as metal adsorbent : Sorption of lead(II) from aqueous solution onto coirpith carbon

Abstract: Activated carbon prepared from coirpith waste was used for the adsorptive removal of Pb(II) from aqueous solution. Parameters such as agitation time, metal ion concentration, adsorbent dose and pH were studied. Adsorption equilibrium was reached in 30 min for solution containing 25 and 50 mg l−1 and 40 min for solution containing 75 and 100 mg l−1 Pb(II), respectively. Adsorption parameters were determined using both Langmuir and Freundlich models. The adsorption capacity was 263 mg g−1. Pb(II) removal increased with increased pH from 2 to 4 and remained constant up to pH 10. Desorption studies were also carried out with dilute hydrochloric acid to recover both carbon and Pb(II). As the raw material for the preparation of activated carbon is discarded as waste during coir processing, the production of this carbon is expected to be economically feasible.

Variation of Langmuir adsorption constant determined for TiO2-photocatalyzed degradation of acetophenone under different light intensity

Abstract: The Langmuir–Hinshelwood (L–H) kinetic model has been used to describe semiconductor photocatalysis. In this report, the L–H rate constant (kL–H)and the Langmuir adsorption constant (K) have been determined under different light intensity for the photocatalytic degradation of poorly adsorbed acetophenone over TiO2 of Degussa P25 in aqueous medium (pH 6.2). The result shows that K decreases when the irradiation is performed at higher light intensity, while kL–H increases expectedly. It is also demonstrated that the initial time interval selected for the initial rate calculation is quite critical to the final determination for the constants.

Comparison of Linear and Nonlinear Forms of Isotherm Models for Strontium Sorption on a Sodium Bentonite

Abstract: Sorption on bentonite will play an important role in retarding the migration of radionuclides from a waste repository. Bentonite is characterized by low permeability, water swelling capability and excellent sorption potential for cationic radionuclides. To correctly assess the sorption potential of radionuclides on bentonite is essential for the development of predictive migration models. The sorption isotherm model is usually used to describe the sorption behavior and assess the sorption potential of radionuclides on bentonite. However, there are few studies to investigate the feasibility of isotherm models for the sorption of radionuclides on bentonite. Thus, in this study, we compared the goodness-of-fit of linear and nonlinear forms of two common isotherm models, Langmuir and Freundlich equations. The experimental sorption isotherms of strontium (Sr) on Wyoming bentonite, MX-80, were used for illustration. The results showed that the nonlinear forms of Langmuir and Freundlich isotherm models are more suitable for fitting the experimental sorption isotherms of Sr on MX-80 than are the linear forms. Thus, the nonlinear forms of isotherm models should be primarily adopted to fit experimental isotherms. On the other hand, we also found that the goodness-of-fit of Langmuir model is better than that of Freundlich model. Moreover, based on the theoretical assumptions of Langmuir isotherm model, the parameters M and K L represent the sorption capacity and affinity, respectively. One can use the values of M and K L , obtained from fitting the experimental isotherms, to assess the sorption potential of radionuclides in bentonite. Thus, we suggested that the Langmuir isotherm model is more useful for investigating the sorption behavior of radionuclides on bentonite.

Sticking Probabilities in Adsorption of Alkanethiols from Liquid Ethanol Solution onto Gold

Abstract: The sticking probability (ie, the rate of adsorption per molecular collision with the surface) is the most fundamental and powerful way to express adsorption rate constants, yet its accurate use has been restricted almost exclusively to adsorption from the gas phase Here, we extend this concept to transient rate measurements of adsorption from liquid solutions, and apply it to clarify the dynamics of alkanethiol adsorption on gold A numerical solution to Fick's law of diffusion, using the measured adsorption rate versus time as a boundary condition, provides the adsorbate concentration versus distance from the surface and time The resulting concentration nearest the surface gives the collision frequency with the surface, used to calculate the sticking probability Quantitative measurements of adsorption kinetics of a series alkanethiols onto gold from ethanol solutions by surface plasmon resonance (SPR) spectroscopy reveal first-order Langmuir kinetics up to a coverage of ∼4 × 1014 molecules/cm2, wit

Adsorption and bio-degradation of phenol by chitosan-immobilized Pseudomonas putida (NICM 2174)

Abstract: Biodegradation of phenol by Pseudomonas putida (NICM 2174), a potential biodegradent of phenol has been investigated for its degrading potential under different conditions. Pseudomonas putida (NICM 2174) cells immobilized in chitosan were used to degrade phenol. Adsorption of phenol by the chitosan immobilized matrix played an important role in reducing the toxicity of phenol. In the present work, results of the batch equilibrium adsorption of phenol on chitosan from its aqueous solution at different particle sizes (0.177 mm, 0.384 mm, 1.651 mm) and initial concentration of phenol (20, 40, 60, 80, 100, 120, 140, 160, 180, 200 mg/l) have been reported. The adsorption isotherms are described by Langmuir, Freundlich and Redlich-Peterson types of equations. These indicate favourable adsorption with chitosan. From the adsorption isotherms, the adsorption capacity, energy of adsorption, number of layers and the rate constants were evaluated. In batch kinetic studies the factors affecting the rate of biodegradation of phenol, were initial phenol concentration (0.100 g/l, 0.200 g/l, 0.300 g/l), temperature (30 °C, 34 °C, 38 °C) and pH (7.0, 8.0, 9.0). Biodegradation kinetic data indicated the applicability of Lagergren equation. The process followed first order rate kinetics. The biodegradation data generally fit the Lagergren equation and the intraparticle diffusion rate equation from which adsorption rate constants, diffusion rate constants and diffusion coefficients were determined. Intraparticle diffusion was found to be the rate-limiting step. Cell growth contributed significantly to phenol removal rates especially when the degradation medium was supplemented with a utilizable carbon source.

From nucleation to engineering of crystalline architectures at air-liquid interfaces

Abstract: The packing arrangements of Langmuir films on aqueous solution of simple amphiphiles, such as fatty acids, alcohols, amides, and amino acids, are now established to near atomic resolution by the me...

Effect of pH and ionic strength on the interaction of humic acid with aluminium oxide

Abstract: The effect of pH and neutral electrolyte on the interaction between humic acid/humate and γ-AlOOH (boehmite) was investigated. The quantitative characterization of surface charging for both partners was performed by means of potentiometric acid–base titration. The intrinsic equilibrium constants for surface charge formation were logK a,1 int=6.7±0.2 and logK a,2 int = 10.6±0.2 and the point of zero charge was 8.7±0.1 for aluminium oxide. The pH-dependent solubility and the speciation of dissolved aluminium was calculated (MINTEQA2). The fitted (FITEQL) pK values for dissociation of acidic groups of humic acid were pK 1 = 3.7±0.1 and pK 2 = 6.6±0.1 and the total acidity was 4.56 mmol g−1. The pH range for the adsorption study was limited to between pH 5 and 10, where the amount of the aluminium species in the aqueous phase is negligible (less than 10−5 mol dm−3) and the complicating side equilibria can be neglected. Adsorption isotherms were determined at pH ∼ 5.5, ∼8.5 and ∼9.5, where the surface of adsorbent is positive, neutral and negative, respectively, and at 0.001, 0.1, 0.25 and 0.50 mol dm−3 NaNO3. The isotherms are of the Langmuir type, except that measured at pH ∼ 5.5 in the presence of 0.25 and 0.5 mol dm−3 salt. The interaction between humic acid/humate and aluminium oxide is mainly a ligand-exchange reaction with humic macroions with changing conformation under the influence of the charged interface. With increasing ionic strength the surface complexation takes place with more and more compressed humic macroions. The contribution of Coulombic interaction of oppositely charged partners is significant at acidic pH. We suppose heterocoagulation of humic acid and aluminium oxide particles at pH ∼ 5.5 and higher salt content to explain the unusual increase in the apparent amount of humic acid adsorbed.