Showing papers on "Langmuir published in 1995"

Description of two-metal biosorption equilibria by Langmuir-type models.

Abstract: A biosorbent prepared from Ascophyllum nodosum seaweed biomass, FCAN2, was examined for its sorption capacity. Equilibrium batch sorption studies were performed using two-matal systems containing either (Cu + Zn), (Cu + Cd), or (Zn + Cd). In the evaluation of the two-metal sorption system performance, simple isotherm curves had to be replaced by three-dimensional sorption isotherm surfaces. In order to describe the isotherm surfaces mathematically, three Langmuir-type models were evaluated. The apparent one-parameter Langmuir constant (b) was used to quantify FCAN2 "affinity" for one metal in the presence of another one. The uptake of Zn decreased drastically when Cu or Cd were present. The uptake of Cd wasmuch more sensitive to the presence of Cu than to that of Zn. The presence of Cd and Zn alter the "affinity" of FCAN2 for Cu the least at high Cu equilibrium concentrations. The mathematical model of the two-metal sorption system enabled quantitative estimation of one-metal (bio)sorption inhibition due to the influence of a second metal. (c) 1995 John Wiley & Sons Inc.

Effect of Inert Supports for Titanium Dioxide Loading on Enhancement of Photodecomposition Rate of Gaseous Propionaldehyde

Abstract: Effects of the use of inert supports for TiO2 loading on photocatalyzed decomposition of propionaldehyde in the gas phase was investigated for mordenite support with various amounts of TiO2 loading and for several kinds of supports such as other zeolites, alumina, silica, and activated carbon. The adsorption constant and the amount of adsorption of propionaldehyde were evaluated for TiO2-loaded supports by obtaining Langmuir adsorption isotherms. By correlating these parameters to the photodecomposition rates of propionaldehyde, the involvement of the support in the photodecomposition reaction is clarified. The photocatalytic activity of TiO2 on mordenite having various amounts of TiO2 loading increases with increase in the amount of loaded TiO2 up to an optimum value (ca. 50 wt %), beyond which a decreasing tendency of the activity appeared. In the region of ascending activity, plenty of adsorbed substrate is available and the activity is controlled by the content of TiO2, while in the region of descending activity, the decrease in the amount of adsorbed substrate due to a decrease in the occupancy of the support by the TiO2 loading is responsible for the activity decrease. The photocatalytic activities are greatly influenced by the kind of inert supports used and show a volcano type dependence on the adsorption constant of the TiO2-loaded supports. In cases where the adsorption constant is low, the decomposition rate is determined by the amount of adsorbed substrate, while if the adsorption constant is very high, plenty of adsorbed substrate is available on the support, but it is not mobile to the loaded TiO2. We conclude that the use of an inert support having a medium adsorption constant is necessary to obtain the highest activity, where a high amount of adsorbed substrate that can be supplied to TiO2 particles is available.

Isotherm analyses for single component and multi-component metal sorption onto lignite

Abstract: The adsorption of the three metal ions, copper, cadmium and zinc in single component and multi-component mixtures in aqueous solutions by lignite is reported. A comparison is made between the single component saturation uptake and the multi-component uptakes. The isotherms indicate a competitive uptake with copper being preferentially absorbed by the lignite in multi-component solutions. The isotherms are plotted to obtain the Langmuir constants, the Freundlich constants and the Redlich–Peterson constants. Lignite is shown to possess an affinity for the metal ions which make its use as an adsorbent a possible alternative to the use of more expensive activated carbons.

Biosorption of heavy metals by Zoogloea ramigera: use of adsorption isotherms and a comparison of biosorption characteristics

Abstract: The biosorption of lead(II), copper(II), nickel(II), and iron(III) ions on Zoogloea ramigera, an activated sludge bacterium, was studied with respect to adsorption pH and temperature in order to determine the optimum conditions for heavy metal removal. Optimum initial pH for the biosorption of lead(II), nickel(II) and copper(II) ions by Z. ramigera was determined as 4.0–4.5 whereas higher biosorptive uptake of iron(III) ions by Z. ramigera was obtained at pH 2.0. Maximum biosorption rates of nickel(II) and copper(II) ions by Z. ramigera where obtained at 25°C, while the initial biosorption rates and the adsorptive capacity of the biomass for lead(II) and iron(III) ions increased with increasing temperatures in the range 25–45°C. The adsorption isotherms were developed for optimum conditions and it was seen that the adsorption equilibrium data fit both Freundlich and Langmuir isotherms within the metal ion concentrations studied (25–200 mg 1−1). The adsorption constants for lead(II) and iron(III) were higher than those for nickel(II) and copper(II) for both Langmuir and Freundlich models.

Absorption of heavy metals from waste streams by peat

Abstract: Adsorption of heavy metal ions (e.g. copper, nickel and lead) onto sphagnum moss peat was investigated. The influence of pH, concentration, temperature, nature of solute, number of solutes simultaneously present, peat dose and reaction time on batch adsorption equilibria and kinetics tests were examined. Batch adsorption of copper and nickel onto peat was pH dependent, the optimum range being 4.0 to 5.0 for copper and 4.0 to 7.0 for nickel. Langmuir and Freundlich isotherms showed a single relationship between initial metal concentration, metal removal, and initial pH. The latter was found to control efficiency of metal removal. The use of peat in removal of lead from aqueous solution was studied in batch experiments. Investigations included the effect of pH and temperature of adsorption. The adsorption equilibria data followed Langmuir and Freundlich models. Efficiency of lead removal depended very little on the reaction temperatures (12 to 37°C) and initial pH values (4.0 to 6.0). The results suggested that the adsorption process is endothermic for lead-peat adsorption. Kinetic data suggested involvement of a chemical rate-limiting step, and a predictive relationship was derived relating metal removal to peat dose. In comparison with other metals, nickel removal is poor, and possible reasons are discussed. Kinetic results also indicated that pore diffusion is not the only rate determining step in peat metal adsorption. A rate equation is described for the study of the kinetics of adsorption of aqueous divalent metal ions onto sphagnum moss peat for a range of conditions. An empirical model was devised for predicting percentage metal ion adsorbed. The model showed a high coefficient of correlation, indicating its reasonableness. The last section describes the results of an examination into the simultaneous adsorption by peat of several metals. Initially copper and nickel from both single- and bi-solute systems were tested. In general, pore diffusion appeared to be the rate-controlling step. The effects of competitive adsorption in batch systems for copper and nickel system was also studied in various ratios of metal concentration. A mathematical model was used successfully and shown to be predictive for various ratio of metal ions concentration in competitive adsorption. The dose effect on the uptake of metals on moss peat was also studied for bi-solute adsorption systems. The best interpretation which could be placed on the data was that the behaviour of nickel was unusual. The results also showed that the kinetics of adsorption were best described by a second-order expression rather than a first-order model. For metal ions which are of different size but are divalent metal ions, we used lead(II) and copper(II) as well as lead(II) and nickel(II) systems. The effects of competitive adsorption in batch systems indicated that copper had a greater effect on lead adsorption than did nickel. However, lead had a greater effect on nickel than copper. A copper, lead and nickel triple-solute system was also tested. The adsorption of any single metal such as copper, lead and nickel was hindered by the presence of the other metals. The competitive effect appears to have affected the three ions in the order nickel > lead > copper with nickel affected most; the adsorption capacity for each solute from the mixed solution was 15.9, 57.4 and 71.5% of that of a single-solute system for copper, lead and nickel, respectively. The kinetic results showed that the heavy metals are adsorbed fairly rapidly, and that there is a relatively good fit between experimental data and the second order model for copper, lead and nickel.

Adsorption of Branched and Cyclic Paraffins in Silicalite. 1. Equilibrium

Abstract: Gravimetric equilibrium isotherms are reported for adsorption of branched and cyclic C[sub 6] paraffins on silicalite. In addition to the isotherms, Henry constants and heats of adsorption are reported for 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane, 2,3-dimethylbutane, methylcyclopentane, and cyclohexane. Adsorption capacities are in the range of 4--7 wt%. All isotherms are of type 1 in Brunauer's classification. Adsorption saturation limits, estimated from the experimental results by Langmuir regression, show a decreasing trend with increasing temperature. Adsorption equilibrium constants follow the trend double-branched < single-branched < cyclic paraffins. Heats of adsorption for the single-branched paraffins increase slightly with loading, but for the double-branched and cyclic paraffins the variation of heat of adsorption with coverage is more pronounced.

Quartz Crystal Microbalance and Surface Plasmon Resonance Study of Surfactant Adsorption onto Gold and Chromium Oxide Surfaces

Abstract: The adsorption of two nonionic surfactants on hydrophobic gold and hydrophilic chromium oxide surfaces from aqueous solution has been investigated using a quartz crystal microbalance (QCM) and surface plasmon resonance (SPR). Adsorption isotherms for a nonyl phenol ethoxylate with average ethylene oxide chain length of 9 (N9) on gold and for octaethylene glycol monododecyl ether (C12E8) on both gold and chromium oxide surfaces have been measured by QCM. Isotherms for N9 and C12E8 on the gold surface can be described by Langmuir adsorption, while that of C12E8 on the chromium oxide surface was S-type. Complementary SPR experiments of C12E8 adsorption onto gold suggest that the resonance frequency change of the QCM crystal in solution with adsorbed C12E8 (at saturation coverage) is 80% greater than that predicted by the Sauerbrey equation for air measurements. This implies a 2.08 Hz/ng change for the QCM in contact with aqueous solution. This calibration factor was used to calculate the saturated surface coverage for the surfactants (and hence area per surfactant) at the solid/liquid interface. These data are in good agreement with those reported in the literature for N9 and C12E8 adsorbed onto various hydrophobic and hydrophilic surfaces. © 1995, American Chemical Society. All rights reserved.

Effects of pH and Inorganic Salts on the Adsorption of Phenol from Aqueous Systems on Activated Decolorizing Charcoal

Abstract: An experimental investigation of the effects of pH and three inorganic salts (KCl, KI, and NaCl) on the adsorption isotherms of phenol (from a dilute aqueous solution) on activated charcoal was conducted. Each salt was studied at three different concentrations, i.e., 0.1, 0.001, and 0.005 M. The effect of pH (in the pH range 3 to 11) in the presence of KI, KCl, and NaCl was also investigated. The concentration of phenol in the aqueous systems studied ranged from 10 to 200 ppm. The temperature effect was also studied, and the resulting experimental equilibrium isotherms at 30, 40, and 55°C are well represented by Freundlich, Langmuir, and Redlich—Paterson isotherms. The relevant parameters for these isotherms are presented.

Influence of adsorbate size and adsorbent heterogeneity of IAST

Abstract: The ideal adsorbed solution theory (IAST) can introduce serious errors in the calculation of multicomponent gas adsorption equilibria from the corresponding pure gas adsorption isotherms when the adsorbate sizes and the degree of adsorbent heterogeneity for adsorption of the components differ substantially. The multisite Langmuir and heterogeneous Langmuir models were used to evaluate the extent of these errors. It is shown that large diferences in adsorbate sizes and degrees of heterogeneity of adsorption of the components of a mixture can cause the formation of an adsorption azeotrope that cannot be described by IAST.

Sticking probabilities for co adsorption on pt(111) surfaces revisited

Abstract: The coverage dependence of the sticking probability for carbon monoxide on Pt(111) surfaces was investigated by using the dynamic method originally devised by King and Wells. The CO uptake was studied as a function of CO beam flux, surface-to-doser distance, and surface temperature. The sticking probability on the clean surface was found to be quite high in all cases, about 0.8, and to remain approximately constant at low temperatures up to coverages close to 0.50 monolayers (ML), at which point a c(4x2) ordered layer forms on the surface. This behavior is explained by a model originally proposed by Kisliuk where the molecules adsorb on a highly mobile extrinsic precursor state before migrating to their final chemisorbed state. Above 0.50 ML the sticking probability then drops suddenly, presumably because the chemisorption energy drops as compressed CO layers start to form on the surface. The effect of inhomogeneities in the spatial distribution of the CO beam across the surface was studied by changing the distance between the sample and the doser, which was found to affect the overall shape of the CO uptake curves. Finally, the adsorption kinetics was determined as a function of surface temperature: the uptake was found to changemore » from precursor mediated below 200 K to a more Langmuir type behavior around room temperature. 44 refs., 12 figs., 1 tab.« less

Adsorption of Salmon Calcitonin to PLGA Microspheres

Abstract: Purpose. The interaction of salmon calcitonin (sCT) and poly (d,llaetide-co-glycolide) was detected during preparation and evaluation of microspheres. The purpose of this study was to quantitate the extent and nature of the interaction. Methods. Blank microspheres were prepared by an aqueous emulsification solvent extraction technique. Adsorption studies were carried out at six concentrations of sCT and three concentrations of microspheres. Adsorption^isotherms were constructed using the Langmuir and Freundlich treatments. Results. Adsorption at I mg/ml sCT concentration resulted in almost complete depletion of the peplide from the adsorption medium with the time to reach maximum adsorption decreasing with increasing microsphere concentration. At sCT concentrations below 100 ^ig/ml, a true equilibrium occurred in 1 hour or less while at higher concentrations (up to 350 p-g/ml), a transient equilibrium was reached in 1 to 2 hours, followed by further adsorption of the peptide. The adsorption followed the Lang.-nuir isotherm at concentrations below 200 (Jig/mi, indicating formation of a monolayer. Multilayer interaction, described by (he Freundlich isotherm, occurred at higher concentrations and resulted in complete depletion of sCT from the adsorption medium. The affinity constant during monolayer formation was 0.09 and the plateau surface concentration was 5.1 Hg/mg. The multilayer peptide-pcplide adsorption showed a iower affinity (0.025) but higher capacity (24 p.g/mg» than the monolayer peptide-polymer adsorption. Conclusions. The results show that poly (d.l-lactide-co-glycolide) microspheres have a high adsorption capacity for sCT which must be considered in formulating a controlled delivery product of this peplide.

Sulfur Dioxide Sorption Properties and Thermal Stability of Hydrophobic Zeolites

Abstract: Adsorption isotherms of SO{sub 2} in air on hydrophobic dealuminated Y (DAY) zeolite and silicalite at SO{sub 2} partial pressures ranging from 0.5 to 5 kPa were measured by the gravimetric method. The SO{sub 2} sorption isotherms on these two zeolites at different temperatures (25--100 C) can be correlated by the langmuir equation at low SO{sub 2} pressures (< 2 kPa) and by the Freundlich equation in the whole SO{sub 2} pressure range studied. The sorption capacity of SO{sub 2} on silicalite is larger than that of the DAY zeolite. Selective surface adsorption rather than the pore-filling mechanism was observed on adsorption equilibrium in these two zeolites. The SO{sub 2} sorption and desorption kinetic data obtained on these two zeolites show the dominant role of the reaction of SO{sub 2} on the zeolite surface in the SO{sub 2} sorption or desorption process. The simple Langmuir adsorption kinetic model provides a good description of SO{sub 2} sorption and desorption kinetics on these two zeolites at low SO{sub 2} partial pressures. The thermal stability of these two zeolites was studied by comparing the pore texture, crystalline structure, and SO{sub 2} adsorption ability of the fresh samples with those of the thermally treatedmore » samples at 550 or 850 C under various caustic conditions. It was found that these two zeolites are thermally and chemically stable under the studied conditions.« less

Sorption of heavy metals to Phormidium laminosum biomass

Abstract: The capacity to adsorb a number of heavy metals [Fe(II), Cr(III), Cd(II), Pb(II), Zn(II), Cu(II) and Ni(II)] by heat-dried biomass of the non-N 2 -fixing cyanobacterium Phormidium laminosum was examined. Pretreatment of biomass with alkaline (1 M NaOH or Na 2 CO 3 ) washes led to increased metal adsorption, whereas acid treatment was inadequate. Exopolysaccharides present in the mucilaginous layer covering nitrogen-starved cells did not improve the adsorption capacity of the biomass. Biosorption was a very fast and pH-dependent process for most metals investigated. Generally, binding showed a minimum at pH < 3, but increased clearly with pH and reached a maximum at about pH 6-7. In contrast, the amount of metal bound increased with the biomass and the amount of available metal. Constants from Langmuir isotherms were calculated and the order of relative affinities for the studied metals was established according to the sorption intensity. Far from being reduced, the biosorption of the tested metals, with the exception of Ni(II), was slightly enhanced in the presence of high concentrations of Ca 2+ (up to 200 p.p.m.). Finally, desorption attempts with 0.1 M H 2 SO 4 succeeded to different degrees depending on the metal. Alkaline-conditioned biomass of P. laminosum can constitute an interesting and novel biosorbent of heavy metals to depollute wastewaters, even in hard waters containing a high concentration of Ca2 + .

Adsorption-desorption of 2,4,6-trinitrotoluene and hexahydro-1,3,5-trinitro-1,3,5-triazine in soils

Abstract: This study studied the adsorption-desorption behavior of TNT (2, 4, 6-trinitrotoluene) and RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) in a bentonite/sand reference material (Swy-1 montmorillonite clay mixed with acid-washed sand) and two selected soils (Norwood and Kolin). Release of TNT,RDX, and other compounds from a contaminated soil obtained from the Louisiana Army Ammunition Plant (AAP) site was also investigated. The kinetics of TNT and RDX retention were measured using batch methods for a range of input concentrations. For RDX, the adsorption isotherms were distinctly linear. The TNT adsorption isotherm for bentonite/sand mixture appeared linear and was described equally well using linear, Freundlich, Langmuir, and a modified Langmuir model. For the Norwood and Kolin soils, TNT adsorption isotherms exhibited distinct nonlinearity and the Freundlich model provided the best fit. As indicated by the K{sub d} values, TNT exhibited stronger retention or affinity to all soils and the bentonite/sand mixture than for RDX. The RDX retention data indicated little time-dependent behavior. The TNT retention data indicated a continued decrease in TNT concentration with time in the Norwood and Kolin soils. This was possibly caused by the formation and subsequent adsorption of transformation products because transformation products, such as amino nitro toluene compounds, were identified during batchmore » experiments. For the bentonite/sand mixture, TNT retention was rapid initially and reached apparent equilibrium within 1 day. Unlike Kolin and Norwood soils, there was no hysteretic behavior of TNT adsorption-desorption by the bentonite/sand mixture and a mass balance suggested fully reversible retention mechanisms. 15 refs., 13 figs., 2 tabs.« less

Cadmium biosorption by Streptomyces pimprina waste biomass

Abstract: Biosorption of cadmium from solution was studied using a hamycin-producing Streptomyces pimprina waste biomass. Mycelial pretreatments with 80% ethanol increased the uptake of cadmium threefold. The rate of uptake of the metal was maximum in the first 10 min and the equilibration of the system was achieved after 60 min. At pH 2.0 there was no adsorption of cadmium; however, as the pH of the solution increased, a rise in the adsorption could be noticed, which peaked at pH 5.0. The uptake of cadmium was found to increase linearly as a function of cadmium concentration up to 500 mg/l. The data could be fitted to Freundlich and Langmuir models for absorption processes. A 0.1 M EDTA solution could desorb cadmium loaded on S. pimprina biomass with the highest efficiency.

Is Langmuir Circulation Driven by Surface Waves or Surface Cooling

Abstract: The ratio of the buoyancy force driving thermal convection to the surface wave vortex-force driving Langmuir circulation in the Craik–Leibovich mechanism involves the Hoenikker number Ho. The critical value Hoc, at which wave forcing and thermal convection contribute equally to the circulation, is found to increase with decreasing Langmuir number La and approaches 3 in the small La limit. For a typical wind speed and surface cooling, Ho is of order O(10−2) to O(10−1). Thus, wave forcing dominates over thermal convection in driving Langmuir circulation. Stratification induced by strong surface heating suppresses the circulation generated by wave forcing and could completely inhibit the CL instability. In the physically plausible range of −0.1 < Ho < 0, however, this does not happen for small La and the dynamical effect of heating is very small. For a given heat flux, the temperature difference between the regions of surface divergence and convergence in Langmuir circulation depends on Ho, Pr, and ...

Comparative Study of Langmuir Monolayers of Immunoglobulin G Formed at the Air-Water Interface and Covalently Immobilized on Solid Supports

Abstract: Langmuir films of IgG formed at the air-water interface and covalently immobilized on solid supports were studied by means of fluorometry and ellipsometry. Dependencies of monolayer molecular density and thickness on surface pressure were determined. The data obtained make possible a model of the film molecular organization and its dependence on the surface pressure. The films are of monomolecular layer character within the entire range of achievable pressures on the air-water interface as well as on the solid supports. The molecular orientation changes with the pressure. In the monolayer on the air-water interface the molecules are positioned with their Fab-Fab-Fc ploane parallel to the surface at pressures below 20 mN/m ; when compressed up to 35 mN/m, they turn by 90° to reach perpendicular position with respect to the surface. Within the range 20 mN/m < π < 35 mN/m the angle of molecular inclination increases monotonically from 0° to 90° with pressure. The pattern of the orientation-pressure behavior for transferred monolayers is almost the same showing that the film molecular structure does not change upon deposition on to the solid activated substrate.