Showing papers on "Langmuir published in 1999"
TL;DR: In this article, the authors used the Freundlich and Langmuir adsorption models for describing the short-term biosorption of copper(II), nickel(II) and chromium(VI) by all three algae species.
560 citations
TL;DR: In this paper, the effect of coal composition upon pore structure and adsorption characteristics of four bituminous coals of the Cretaceous Gates Formation coal is investigated.
523 citations
TL;DR: In this article, the ability of five low-cost adsorbents, namely rice husk, cotton, cotton waste, hair and coal, to adsorb two basic dyes, namely, Safranine and Methylene Blue, has been studied Equilibrium isotherms have been determined and analyzed using the Langmuir equations.
Abstract: The ability of five low cost adsorbents – rice husk, cotton, bark, hair and coal – to adsorb two basic dyes, namely, Safranine and Methylene Blue, has been studied Equilibrium isotherms have been determined and analysed using the Langmuir equations The monolayer saturation capacities for Safranine are 1119, 838, 875, 190 and 120 mg g-1adsorbent and for Methylene Blue are 914, 312, 277, 158 and 250 mg g-1adsorbent for bark, rice husk, cotton waste, hair and coal respectively A limited number of fixed bed column studies have been performed and the bed depth service time for each dye-adsorbent system has been determined
409 citations
TL;DR: In this paper, the adsorption of phosphate ions from aqueous solution onto thin films of colloidal TiO2 has been studied for the first time by in situ internal reflection infrared spectroscopy.
Abstract: The adsorption of phosphate ions from aqueous solution onto thin films of colloidal TiO2 has been studied for the first time by in situ internal reflection infrared spectroscopy. Phosphate binds strongly to TiO2, as evidenced by the large changes in the PO stretching band structure in the infrared spectrum of the adsorbed species compared with the solution species. The Langmuir binding constant for phosphate onto TiO2 at pH = 2.3 is (3.8 ± 0.8) × 104 dm3 mol-1, which is similar to the binding constants onto TiO2 for bidentate ligand species such as oxalate and catechol. The strength of the binding is also apparent in the kinetics of adsorption, showing fast adsorption and much slower desorption, as expected for a strongly bound species. The kinetics data at pH = 8.3 have indicated coverage-dependent phosphate adsorption and desorption. Experiments with substituted phosphate species have confirmed the bidentate binding of phosphate to Ti(IV) ions at the TiO2 surface.
369 citations
TL;DR: In this paper, the sorption of three acid dyes, namely, Acid Red 114, Polar Yellow and Polar Blue RAWL, onto activated carbon, has been studied and the equilibrium isotherms have been measured for three single component systems (AB, AR, AY) and one binary component system (AB+AY).
Abstract: The sorption of three acid dyes, namely, Acid Red 114, Polar Yellow and Polar Blue RAWL, onto activated carbon, has been studied. Equilibrium isotherms have been measured for three single component systems (AB, AR, AY) and one binary component system (AB+AY). The isotherms were determined by shaking 0.05 g activated carbon, particle size range 500–710 μm, with 0.05 dm3 dye solution of initial concentrations from 10 to 250 mg/dm3. A constant temperature agitating 400-rpm shaking water bath was used and the temperature maintained at 20±2°C. A contact time of 21 days was required to achieve equilibrium. Analysis of data has been carried out in two stages. (a) In single component analysis, the experimental isotherm data were analysed using Langmuir, Freundlich, Redlich-Peterson, Temkin and Dubinin-Radushkevich equations for each individual dye. The monolayer adsorption capacities are 101.0 mg Acid Red per g carbon, 100.9 mg Acid Blue per g carbon and 128.8 mg Acid Yellow per g carbon. (b) In multicomponent analysis, one binary system has been analysed using an extended form of the Langmuir equation. The correlation between theoretical data and experimental data only had limited success due to competitive and interactive effects between the dyes and dye-surface interactions.
359 citations
TL;DR: Adsorption studies of mercury (II) from aqueous solutions on coirpith carbon were investigated under the varying conditions of agitation time, metal ion concentration, adsorbent dose and pH as discussed by the authors.
287 citations
TL;DR: Adsorption by activated red mud (ARM) is investigated as a possible alternative to the conventional methods of Cr(VI) removal from aqueous synthetic solutions and industrial effluents, and promising results are obtained.
235 citations
TL;DR: In this article, the formation kinetics of n-alkanethiols on polycrystalline gold surfaces were studied in situ and in real time under a variety of experimental conditions.
Abstract: Thiolate formation of n-alkanethiols (CH3(CH2)m-1SH) adsorbing on polycrystalline gold was studied in situ and in real time under a variety of experimental conditions. The chain length of the thiols studied varied from m = 4 to m = 22. The influence of the thiol concentration in different solvents (ethanol, hexane, dodecane, and hexadecane) was examined in the range between 0.5 and 20.0 μmol/L. Among the models proposed in the literature, only Langmuir kinetics can explain the data, irrespective of the experimental conditions. As will be shown, all other kinetic models fail to describe the measured formation kinetics of thiolate films on a polycrystalline gold surface. However, small but significant differences between the experimental data and the Langmuir model assuming statistical adsorption are identified. A modified Kisliuk model accounting for different adsorption sites yields the best agreement with the experimental data. On the basis of these results we propose a kinetic model of thiolate formatio...
193 citations
TL;DR: In this article, the adsorption of gold(III) ions onto chitosan and N-carboxymethyl (NCMC) has been investigated as a function of pH, agitation period, and concentration of Au3+ ions.
Abstract: The adsorption of gold(III) ions onto chitosan and N-carboxymethyl chitosan (NCMC) has been investigated. Experiments were carried out as a function of pH, agitation period, and concentration of Au3+ ions. It was shown that the adsorption of Au3+ ions occurred only at the optimum pH. Kinetic studies showed a rapid adsorption of Au3+ from aqueous solution. Adsorption isothermal data could be interpreted by the Langmuir equation. Langmuir constants have been determined. The experimental data of the adsorption equilibrium from Au3+ solutions correlated well with the Langmuir isotherm equation. The uptake of Au3+ on chitosan and NCMC were 30.95 mg/g of chitosan and 33.90 mg/g of NCMC. The Au3+ ions were readily removed from chitosan and NCMC by treatment with an aqueous EDTA solution.
164 citations
TL;DR: All adsorption data, and the results of potentiometric titrations of kaolinite suspensions (alone and in the presence of metals at 100 µM), can be fitted closely by a constant-capacitance surface complexation model that incorporates two bidentate surface complexes.
149 citations
TL;DR: In this article, the ability of natural zeolites (ZAPS, ZNT and ZN-19) to adsorb pure CO 2, CH 4 and N 2 was studied experimentally.
TL;DR: In this article, the extent of Brilliant Blue FCF adsorption in soils and to identify soil properties that play a predominant role in adsorbing of the dye were investigated, and the results showed that the dye's adorption may increase with decreasing pH due to the prevailing neutral form of the molecule.
TL;DR: It was shown that the isotherm data could not be fit by any conventional two- or three-parameter equation including the Langmuir, Freundlich, BET, and Redlich-Peterson equations over the entire range of concentration (1-32 mol m(-3).
TL;DR: In this article, a generalized Volmer's equation is derived for a multicomponent Langmuir monolayer, which is then used to derive the equations of state for the monolayers of a single amphiphile considering the 2D main phase transition.
Abstract: A generalized Volmer's equation is derived for a multicomponent Langmuir monolayer. This general equation is then used to derive the equations of state for the monolayer of a single amphiphile considering the two-dimensional (2D) main phase transition. A theory developed recently (J. Phys. Chem. 1996, 100, 15478) is extended to incorporate the important case that the area per one amphiphile molecule within the aggregate differs from that characteristic for the nonaggregated amphiphile. The general equation derived involves four parameters, two of which refer to the state of the gaseous monolayer whereas the other two parameters express the 2D aggregation constant and the difference between the area per one amphiphile molecule within the aggregate and the area per one nonaggregated molecule. The experimental Π−A isotherms for Langmuir monolayers of various amphiphiles, either measured by the authors or referred to elsewhere, agree well with the proposed model for physically reliable values of model parameters.
TL;DR: In this article, the binding capacity of the biosorbent was investigated as a function of the initial pH, initial iron(III)-cyanide complex ion and biosorbents concentration.
TL;DR: In this paper, a mass transfer model was developed to describe the overall biosorption rate of cadmium ions in flat seaweed biomass particles, which was solved numerically yielding the effective diffusion coefficient De about 3.5 × 10-6 cm2/s.
Abstract: Biosorption of the heavy metal ion Cd2+ by protonated nonliving brown alga Sargassum fluitans biomass was accompanied by the release of hydrogen protons from the biomass. The uptake of cadmium and the release of proton matched each other throughout the biosorption process. The end-point titration methodology was used to maintain the constant pH 4.0 for developing the dynamic sorption rate. The sorption isotherm could be well represented by the Langmuir sorption model. A mass transfer model assuming the intraparticle diffusion in a one-dimensional thin plate as a controlling step was developed to describe the overall biosorption rate of cadmium ions in flat seaweed biomass particles. The overall biosorption mathematical model equations were solved numerically yielding the effective diffusion coefficient De about 3.5 × 10-6 cm2/s. This value matches that obtained for the desorption process and is approximately half of that of the molecular diffusion coefficient for cadmium ions in aqueous solution.
TL;DR: In this paper, the adsorption of certain beta-lactam antibiotics such as 7-aminocephalosporanic acid, cephalexin, cefadroxyl and 6-aminopenillanic acid in aqueous solution has been studied using polymeric resins of four different types as well as activated carbon.
15 Dec 1999
TL;DR: It was found that some demulsifiers of high molecular weight alter the asphaltene film on water surface in the same way as the resin fraction, i.e., increasing the compressibility of the film which results in a reduced film rigidity.
Abstract: The influence of chemical additives on asphaltene films on water surface and at oil/water interface is studied by means of the Langmuir technique. It was found that some demulsifiers of high molecular weight alter the asphaltene film on water surface in the same way as the resin fraction, i.e., increasing the compressibility of the film which results in a reduced film rigidity. The films that build up at the oil/water interface in model oil systems, containing naturally occurring surfactants, are studied during compression. In this system chemical additives of high molecular weight totally prevent formation of a rigid film at the interface. Adding resins to the bulk phase together with asphaltenes hamper the adsorption of the heavy fraction.
TL;DR: In this paper, the adsorption of iron(III), lead(II), and cadmium(II) ions onto Schizomeris leibleinii, a green alga, was studied with respect to initial pH, temperature, initial metal ion and biomass concentration.
TL;DR: In this paper, the sorption of Cd, Cu, Pb, and Zn ions by Na-rich bentonite, AI and Zr-pillared Na-Rich bentonite (A1-MX80), the uncalcined hydroxy-intercalated precursors (HA1, HZr-MX 80), and commercial Al-Pared bentonite EXM 534 was investigated.
Abstract: The sorption of Cd, Cu, Pb, and Zn ions by Na-rich bentonite, AI and Zr-pillared Na-rich bentonite (A1-MX80, Zr-MX80), the uncalcined hydroxy-intercalated precursors (HA1, HZr-MX80), and commercial Al-pillared bentonite EXM 534 was investigated. Experiments were conducted in ultrapure water and artificial leachate with varying pH. The experiments were performed over periods to 30 wk. Sorption characteristics were described with one and two-site Langmuir isotherms. The non-exchangeable quantities of heavy metals were determined by fusion of the sorbents after ion exchange with ammonium acetate. The sorption of Cd, Cu, Pb, and Zn by bentonite was dominated by cation exchange. In artificial leachate, the sorption was reduced due to competition with alkali and alkaline-earth cations. The sorption of Cu, Zn, and Pb at pH 4.9 and Cd at pH 6.9 by A1 and Zr-hydroxy-intercalated and pillared MX80 was governed also by cation exchange. In contrast, the sorbed quantities of Zn at pH 6.9 exceeded the cation exchange capacity (CEC) of HA1, HZr, A1, Zr-MX80, and EXM 534 and were partially non- exchangeable. The increase of the sorption of Zn with pH and its independence of the ionic strength of the solution at neutral pH suggest a complexation of Zn ions to surface hydroxyl groups of the intercalated A1 and Zr-polyhydroxo cations and pillars. This complexation is the dominating sorption mechanism. Removal of dissolved Zn from solution with time is attributed to surface precipitation. Al-hydroxy and pillared bentonites are considered potential sorbents of Zn ions from neutral pH aqueous solutions, such as waste waters and leachates.
TL;DR: In this paper, a molecular-thermodynamic model for Gibbs monolayers formed from the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (II+), or oxidized II+ (II2+), at the surfaces of aqueous solutions is presented.
Abstract: We report the development of a molecular-thermodynamic model for Gibbs monolayers formed from the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (II+), or oxidized II+ (II2+), at the surfaces of aqueous solutions. This model provides an account of past experimental measurements (Gallardo, B. S.; Metcalfe, K. L.; Abbott, N. L. Langmuir 1996, 12, 4116−4124) which demonstrated electrochemical oxidation of II+ to II2+ to lead to large and reversible changes in the excess surface concentrations and surface tensions of aqueous solutions of this redox-active surfactant. The results of the model lead us to conclude that II+ assumes a looped conformation at the surfaces of aqueous solutions. This looped conformation lowers the surface tensions of aqueous solutions of II+ to ∼49 mN/m at a limiting surface area of 85 A2/molecule (in 0.1 M Li2SO4). The underlying cause of the reduction in surface tension is not an electrostatic contribution to the surface pressure (as is the case with classic...
TL;DR: In this paper, it was shown that the dissociative adsorption of HNO3(g) on NaCl to form NaNO3s and HCl follows single-site Langmuir adaption behavior and that the amount of strongly adsorbed water on the surfaces of NaCl particles strongly depends on the particle size.
Abstract: We show here that the dissociative adsorption of HNO3(g) on NaCl to form NaNO3(s) and HCl(g) follows single-site Langmuir adsorption behavior. X-ray photoelectron spectroscopy is also used to show that the amount of “strongly adsorbed water” on the surfaces of NaCl particles strongly depends on the particle size. Particles of 1−10 μm diameter show large quantities of adsorbed water that remain on the sample up to temperatures of 200 °C. Particles in the size range of 500 μm diameter have less, but still easily measurable, amounts of strongly adsorbed water. Water desorbs completely from low defect density NaCl(100) surfaces under vacuum at temperatures well below room temperature. We present a model for the recently reported HNO3 pressure dependence of the reactive sticking coefficient of HNO3 on NaCl under steady-state reaction conditions. The origin of the pressure dependence in the model is the competition between site blocking on the surface by the build-up of the NaNO3 reaction product and the water-...
Journal Article•
TL;DR: In this paper, the authors investigated tethered chain systems using Langmuir monolayer of polydimethysiloxane-poly styrene (PDMS-PS) diblock copolymers on organic liquids.
Abstract: This article summarizes our investigations of tethered chain systems using Langmuir monolayer of polydimethysiloxane-poly styrene (PDMS-PS) diblock copolymers on organic liquids. In this system, the PDMS block adsorbs to the air surface while the PS block dangles into the subphase liquid. The air surface can be made either repulsive or attractive for the tethered PS chain segments by choosing a subphase liquid which has a surface tension lower or greater than that of PS, respectively. The segment profile of the PS block is determined by neutron reflection as a function of the surface density, the molecular weights of the PS and PDMS blocks, and the solution conditions. We cover the range of reduced surface density (SIGMA) characteristic of the large body of data in the literature for systems of chains tethered onto solid surfaces from dilute solution in good or theta solvent conditions (SIGMA < 12). We emphasize quantitative comparisons with analytical profile forms and scaling predictions. We find that the strong-stretching limit invoked in analytical SCF and scaling theories is not valid over this Z range. On the other hand, over a large portion of this range (SIGMA < 5) tethered layers are well described by a renormalization group theory addressing weakly interacting or noninteracting chains. Simultaneous with the study of the profile form, the free energy of the chains is examined through the surface tension. A strong increase in the surface pressure is observed with increasing surface density which determines the maximum surface density which can be achieved. This apparently nonequilibrium effect is attributed to steric interactions and limited lateral interpenetration. This effect may explain several outstanding discrepancies regarding the adsorption of end-functionalized chains and diblock copolymers onto solid surfaces.
TL;DR: In this article, the NH4 + adsorption data were fitted to the one-and two-surface Langmuir, Freundlich, and Temkin isotherms, and the results showed that the amount of NH4+ adsorbed increased as pH and initial NH4−concentration increased.
Abstract: Clinoptilolite, a zeolite mineral with a high cation exchange capacity and surface area, has ion‐exchange properties that can be utilized to adsorb NH4 +, protecting it from losses during composting of N‐rich animal manures. Ammonium adsorption by the natural zeolite clinoptilolite was studied to ascertain the effectiveness of the zeolite as an NH4 + adsorbent at pH 4, 5, 6, and 7. The NH4 + adsorption data were fitted to the one‐ and two‐surface Langmuir, Freundlich, and Temkin isotherms. All models described the NH4 +adsorption data successfully (r2≥0.939). The one‐surface Langmuir, Freundlich, and Temkin were converted to pH‐dependent forms. The amount of NH4 + adsorbed increased as pH and initial NH4 +concentration increased. From the one‐surface Langmuir isotherm, the NH4 +adsorption capacity (Xm) of the zeolite increased linearly with pH (r2=0.994), and was estimated to be 9,660 mg N kg‐1 at pH4, 11,220 mg N kg‐1 at pH 5, 12,720 mg N kg‐1 at pH 6, and 13,830 mg N kg‐1 at pH 7. The adsorptio...
TL;DR: In this paper, the amounts of equilibrium adsorption of phenol and 4-chlorophenol from aqueous solutions on nonionic polymeric resins were measured in the 288-318 K temperature range.
Abstract: The amounts of equilibrium adsorption of phenol and 4-chlorophenol from aqueous solutions on nonionic polymeric resins were measured in the 288–318 K temperature range. In general, these polymeric resins have a higher capacity for 4-chlorophenol at low solute concentrations but for phenol at higher solute concentrations. The adsorption data for both phenols were presented in terms of the number of adsorbed monolayers and the fraction of pore volume filled due to poor fit by the widely used Langmuir, Freundlich, and BET equations over the entire concentration range (100–3000 g/m3). Finally, the isosteric enthalpies of adsorption were determined. They decreased with increasing surface coverage.
TL;DR: In this paper, the adsorption kinetics and isotherms for cationic and anionic surfactants on coal surfaces were described and evaluated in terms of surface effects and by reference Laplace-Young equation.
TL;DR: In this paper, the MSL (multisite Langmuir) model for homogeneous surfaces was used to correlate all adsorption isotherms by maintaining thermodynamic consistency on model parameters, and it was shown that for paraffins with more than seven carbons it is necessary to account for the effects of lateral interaction of adsorbed molecules.
Abstract: Adsorption equilibrium isotherms of n-paraffins from methane to decane on 5A zeolites (crystals and pellets) were compiled in a wide range of temperature and pressure. The data were correlated using the MSL (multisite Langmuir) model for homogeneous surfaces. It is shown that it is possible to correlate all adsorption isotherms by maintaining thermodynamic consistency on model parameters. However, for paraffins with more than seven carbons it is necessary to account for the effects of lateral interaction of adsorbed molecules. The heat of adsorption for C1−C10 paraffins linearly increases with the carbon number, ranging from 4.6 kcal/mol for methane up to 23.2 kcal/mol for n-decane.
TL;DR: The sorption of Hg(II) in the presence of sodium thiocyanate solution onto polyurethane (PUR) foam, an excellent sorbent, has been investigated and sorption mechanism has been proposed.
TL;DR: In this paper, the kinetics and mechanism of lead biosorption by powderized Rhizopus oligosporus were studied using shake flask experiment and the optimum biomass concentration and initial solution pH for lead sorption at initial lead concentrations ranging from 50-200 mg/l was obtained at 0.5 g/l and pH5, respectively.
Abstract: The kinetics and mechanism of lead biosorption by powderized Rhizopus oligosporus were studied using shake flask experiment. The optimum biomass concentration and initial solution pH for lead sorption at initial lead concentrations ranging from 50–200 mg/l was obtained at 0.5 g/l and pH5, respectively. In term of the ratio of initial lead concentration to biomass concentration ratio, the highest lead adsorption was obtained at 750 mg/g which gave the maximum lead uptake capacity of 126 mg/g. The experimental data of lead sorption by R.oligosporus fitted well to the Langmuir sorption isotherm model, indicating that the sorption was similar to that for an ion-exchange resin. This means that the sorption is a single layer metal adsorption that occurred as a molecular surface coverage. This assumption was confirmed by the examination of lead sorption using transmission electron microscope and energy dispersive X-ray analysis, which showed that during sorption most of the lead was adsorbed on the surface of cell.
TL;DR: A chromium (III) oxide-hydroxide colloid film has been used to model the passive surface of stainless steel in in situ ATR-IR studies of oxalate ion adsorption from aqueous oxalates solutions over a wide pH range.