Thermodynamic Adsorption Model Research Articles

Ultrasound-assisted Aliquat 336 functionalized natural resin for improved removal of Bisphenol-A and Biochanin-A from aqueous solution

Almond resin (a natural polymer) was incorporated with an amine solvent (Aliquat-336) by wet impregnation method in an ultrasonicator. The surface morphology, functional groups, thermal stability, and surface area were determined. The point of zero-charge on the surface was also found out. The performance of the impregnated resin was analyzed by treating Bisphenol-A (BPA) and Biochanin-A (BA) containing aqueous solutions by varying experimental parameters such as dosage amount, contact time, temperature, initial concentrations of BPA and BA, and solution pH. Pseudo-second-order kinetic model and Freundlich isotherm rendered the best fit for BPA and BA adsorption data. A double layer thermodynamic adsorption model was applied to estimate the adsorption energy and positional entropy of the process.

Contamination in Sodium Dodecyl Sulfate Solutions: Insights from the Measurements of Surface Tension and Surface Rheology

The presence of contamination in sodium dodecyl sulfate (SDS) solutions in the form of dodecanol (LOH) is known to drastically affect the resulting interfacial properties such as surface tension (SFT) and rheology. Dodecanol molecules, which are the product of SDS hydrolysis and are inherently present in SDS solutions, have higher surface activity compared to SDS because they are less soluble in water. A characteristic dip in the SFT isotherm is an indicator of the dodecanol contamination in the sample. The presence of an electrolyte in the solution impacts the surface activity of SDS and its critical micelle concentration, and could yield SFT isotherms that closely match those obtained for pure SDS samples. The interpretation of the isotherms in such cases could thus lead to misinterpretation of the surface purity. In this work, we have examined the SFT isotherms for SDS solutions in both the absence and presence of electrolyte. We have fitted the isotherms to three different thermodynamic adsorption models to estimate the amount of dodecanol present in the sample. We have applied the estimated values for the LOH content in a two-component rheological model to predict the viscoelasticity of such surfactant-laden surfaces. We have compared these results with the experimentally measured interfacial rheological properties. Our findings demonstrate that the presence of impurities can be captured under dynamic expansion and contractions, even for solutions containing background electrolyte.

Role of Adsorbate Coverage on the Oxygen Dissociation Rate on Sr-Doped LaMnO3 Surfaces in the Presence of H2O and CO2

Sr-doped LaMnO3 (LSM) is a promising oxygen reduction reaction electrocatalyst in solid oxide fuel cells and other electrochemical devices. The presence of CO2 and H2O has been reported to promote the oxygen dissociation reaction on LSM surfaces. Here, we investigate the coadsorption mechanism of O2 with H2O or CO2 by combining first-principles calculations of the (0 0 1) surface containing 25–100% Sr with thermodynamic adsorption models. The molecules were found to chemisorb by formation of charged oxygen, hydroxide, and carbonate species, and the adsorption energies were exothermic up to monolayer coverage. Low concentrations of H2O or CO2 do not compete with O2 for adsorption sites under relevant conditions. However, their presence contributes to the total amount of oxygen-containing species. The increased coverage of oxygen species provides a quantitative explanation for the reported enhancement in oxygen dissociation kinetics in the presence of H2O/CO2. This study thereby provides insights into oxygen exchange mechanisms on LSM surfaces.

Adsorption of Nickel and Chromium From Aqueous Solutions Using Copper Oxide Nanoparticles: Adsorption Isotherms, Kinetic Modeling, and Thermodynamic Studies

The research was conducted with an aim to assess the efficiency of copper oxide nanoparticles as an adsorbent to remove Ni and Cr. The effect of pH, adsorbent dosage, contact time, initial concentration of metals (Ni and Cr) on the adsorption rate was evaluated and removal of these elements from aqueous solutions was measured using Atomic Absorption Spectrum System (Conter AA700). Moreover, the kinetic and isotherm besides thermodynamic adsorption models were assessed. The highest Ni and Cr removal rate occurred at an optimal pH of 7, and an initial concentration of 30 mg/L, a time period of 30 minutes, and 1 g/L of copper oxide nanoparticles. In fact, with the increase of adsorbent dosage and contact time, the removal efficiency increased and with initial concentration increase of Ni and Cr ions, the removal efficiency reduced. The correlation coefficient of isotherm models viz. Langmuir, Freundlich, Temkin, Redlich-Peterson, and Koble-Corrigan showed that Ni and Cr adsorption via copper oxide nanoparticles better follows the Langmuir model in relation to other models. The results showed that kinetic adsorption of Ni and Cr via copper oxide nanoparticles follows the second order pseudo model with correlation coefficients above 0.99. In addition, the achieved thermodynamic constants revealed that the adsorption process of metals (i.e., Ni and Cr) via copper oxide nanoparticles was endothermic and spontaneous and the reaction enthalpy values for these metals were 17.727 and 11.862 kJ/mol, respectively. In conclusion, copper oxide nanoparticles can be used as effective and environmentally compatible adsorbents to remove Ni and Cr ions from the aqueous solutions

Synthesis of a polymeric imidazolium-embedded octadecyl ionic liquid-grafted silica sorbent for extraction of flavonoids

In this work, a polymeric imidazolium-embedded octadecyl ionic liquid (poly(1-vinyl-3-octadecylimidazolium naphthalene sulfonate))-grafted silica (poly(C18VIm+NapSO3−)@SiO2) sorbent was prepared and applied as a solid-phase extraction (SPE) sorbent in extraction of flavonoids. The synthesized poly(C18VIm+NapSO3−)@SiO2 sorbent was characterized by X-ray photoelectron spectrogram (XPS) and fourier transform infrared spectroscopy (FT-IR). The thermodynamic and kinetic adsorption models of the prepared poly(C18VIm+NapSO3−)@SiO2 sorbent towards flavonoids were discussed by nonlinear fitting adsorption curve and the results indicated the thermodynamic adsorption model in this work was tended to be Freundlich model rather than Langmuir one and the pseudo-second order model could be used to describe the dynamic adsorption process. In addition, the adsorption amounts indicated the sorbent has satisfactory extraction capabities towards flavonoids. For investigating the influence of independent variables and their interactions on the extraction efficiency, a Box-Behnken design was used for optimizing three greatly influential parameters after performing single-factor experiments. The interaction energies between flavonoids and two ionic liquids were calculated to understand the adsorption mechanism. Under the optimal conditions, a method used for determining flavonoids was developed by combining SPE technique with high performance liquid chromatography (HPLC), and the developed method exhibited low limits of detection (0.25–0.4 μg L-1), good linearities with correlation coefficients (R2) in the range of 0.9951–0.9996 and satisfactory recoveries ranging from 83.6% to 114.1%, which confirmed the proposed method could be successfully used to determine trace flavonoids in real samples.

Effect of solution pH on the adsorption of BLG at the solution/tetradecane interface

Using drop profile analysis tensiometry the adsorption dynamics and the equilibrium equation of state of β-lactoglobulin (BLG) at the water/tetradecane (W/TD) interface are studied at pH 3, 5 and 7. The data are well described by a thermodynamic adsorption model using almost identical model parameters for all three pH values except for the surface activity coefficient. The surface pressure isotherms at the water/air (W/A) surface exhibit much steeper run than interfacial pressure at the W/TD interface for any of the studied cases at pH 3, 5 and 7, and the calculated adsorption isotherm data point at smaller adsorbed amounts for these pH. This seems to be in contrast to the much larger interfacial pressure changes reached at high BLG concentrations at the W/TD interface, which are almost three times higher than those at the W/A surface. The observations can be explained by a strong interaction between BLG and the oil molecules at the interface.The dynamic interfacial tensions can be adequately described by a mixed adsorption model, assuming a diffusional transport of the protein molecules in the aqueous bulk phase and an adsorption mechanism which assumes a change of the adsorption activity parameter in dependence of the interfacial coverage.

The Variable Capacitance Model: A Strategy for Treating Contrasting Charge-Neutralizing Capabilities of Counterions at the Mineral/Water Interface

Thermodynamic models predicting ion adsorption at mineral/water interfaces can have limitations from the simplifying assumptions that compact plane thicknesses and capacitance values are constant, and that charge densities of electrolyte counterions of different charge-to-size ratios lie at the same planes of adsorption, or split between different planes. To address these limitations a thermodynamic adsorption modeling framework was developed to account for coexisting compact planes for each type of counterion complexes formed on a single mineral surface. This framework was developed to predict charge development at lepidocrocite (γ-FeOOH) particle surfaces suspended in aqueous solutions of NaCl and NaClO4. The model incorporates properties of Cl(-), ClO4(-), and Na(+) complexes formed at the (001) and (010) faces of this mineral obtained by molecular dynamics (MD) simulations. This concept was incorporated in a thermodynamic adsorption model that predicts an overall variable compact plane capacitance in terms of a linear combination of the capacitances of ion-specific EDL structures scaled for their relative surface loadings. These capacitance values are in turn constrained by compact plane thicknesses of every Cl(-), ClO4(-), and Na(+) complex, based on their MD-derived structures and atomic densities. The model predicts experimental potential-determining (H+, OH-) data for submicrometer-sized synthetic lepidocrocite particles exhibiting both (001) and (010) faces. It also isolates electrostatic contributions from these faces. A computer code solving for this Variable Capacitance Model--VCM--is provided in the Supporting Information section of this article, and can be readily modified to predict molecular-level details of any other mineral/water interface systems using this methodology.

Mineral surface charge development in mixed electrolyte solutions

Effects of competing counterions with different charge-to-size ratios on potential-determining ion (pdi; H+, OH−) adsorption at mineral/water interfaces were resolved in mixtures of aqueous solutions of NaCl and NaClO4 solutions. These effects were monitored on two synthetic goethite (α-FeOOH) particle preparations with distinct charge uptake capacities arising from differences in surface roughness. Charge development at these mineral surfaces was chiefly explored by high precision potentiometric titrations at 25°C. These measurements confirmed that the greater charge-to-size ratio chloride ion not only promoted greater surface charge, but also had pronounced effects in perchlorate-dominated solutions. Cryogenic X-ray photoelectron spectroscopic measurements confirmed that perchlorate retains significant loadings at the goethite surface, even in the presence of chloride. Molecular dynamics simulations of the (110) plane of goethite exposed to these mixed solutions showed that chloride compressed the interfacial region containing electrolyte ions. Perchlorate, on the other hand, is not only present over a thicker region of the interface but also promotes an additional outer-sphere sodium species.These findings were used to develop a thermodynamic adsorption model predicting charge development at these mineral surfaces. The model involves a new formulation accounting for coexisting ion-specific regions each with their distinct compact plane capacitance values. The model can predict charge development in any mixtures of NaCl and NaClO4 contacted with goethite particles of contrasting charge uptake capacities without any additional parameters. This model can also be applied to a broader range of material surfaces.

Adsorption of phenol and chlorophenols onto granular activated carbon and their desorption by supercritical CO2

AbstractBACKGROUNDThe adsorption and desorption of phenol, 2‐chlorophenol (2‐CPh), 4‐chlorophenol (4‐CPh) and 2,4‐dichlorophenol (2,4‐DCPh) were carried out using granular activated carbon (GAC) as adsorbent and supercritical CO2 as regenerant. Adsorption studies at three different temperatures were fitted by using two thermodynamic adsorption models, Langmuir and Toth. The GAC regeneration by CO2 at four different pressures and two temperatures was studied and the design basic parameters were found.RESULTSThe Toth model fitted the experimental data better and thermodynamic properties indicated that this adsorption process was spontaneous, feasible and exothermic. Values of standard enthalpy lower than 40 kJ mol‐1 confirmed that adsorption processes were carried out by physical adsorption. It was also observed that the higher the pressure the higher the regeneration efficiency due to the increase in solvent density.CONCLUSIONGAC presented high selectivity for these substituted phenols and the order of adsorption was 2,4‐DCPh > 4‐CPh > 2CPh > phenol. Supercritical technology was able to regenerate the exhausted GAC, achieving yields comparable with those exhibited by traditional technologies but avoiding additional separation processes. The effective diffusivities of phenols followed the order phenol > 2‐CPh≅4‐CPh > 2,4‐DCPh. © 2013 Society of Chemical Industry

X-ray Photoelectron Spectroscopy of Fast-Frozen Hematite Colloids in Aqueous Solutions. 5. Halide Ion (F–, Cl–, Br–, I–) Adsorption

Halide anion (F(-), Cl(-), Br(-), and I(-)) adsorption and its impact on sodium adsorption at the hematite/water interface were studied by cryogenic X-ray photoelectron spectroscopy (XPS). Measurements were carried out on frozen, centrifuged wet hematite pastes that were previously equilibrated in 50 mM electrolytic solutions in the pH 2-11 range. XPS-derived halide ion surface loadings decreased in the order F(-) > I(-) ≈ Cl(-) > Br(-), whereas sodium loadings were in the order Na(F) > Na(I) > Na(Br) > Na(Cl). The greater sodium loadings in NaF and in NaI resulted from larger anion loadings in these systems. Bromide ion had the lowest loading among all halide ions despite having a charge-to-size ratio that is intermediate between those of Cl(-) and I(-). This unexpected result may have arisen from specific properties of the hematite/water interface, such as water structure and electric double layer thickness. Fluoride ion adsorption proceeded via the formation of hydrogen bonds with the surface hydroxo groups (e.g., ≡Fe-OH(2)···F(-) or ≡Fe-OH···F(-)). Surface-bound fluoride ions exert a greater charge-screening effect than the other halide anions, as demonstrated by considerably small zeta potential values. Fe-F bond formation was excluded as a possible interfacial process as the F 1s peak binding energy (684.2 eV) was more comparable to that of NaF (684.6 eV) than FeF(3) (685.4 eV). Overall, these findings motivate further refinements of existing thermodynamic adsorption models for predicting the ionic composition of hematite particle surfaces contacted with sodium halide aqueous solutions.

Analytical representation of micropores for predicting gas adsorption in porous materials

A straightforward method for the prediction of the gas storage capabilities of porous materials has been established. The Topologically Integrated Mathematical Thermodynamic Adsorption Model (TIMTAM) combines analytical surface potential energies with classical physisorption thermodynamics in a computationally inexpensive fashion. Experimental and simulated isotherms from leading sorbent candidates such as metal–organic frameworks (MOFs), zeolitic imidazolate frameworks (ZIFs), carbon nanotubes and activated carbons have been used to verify the model. Furthermore, the effect of pore size and shape upon gas storage characteristics is explored using the TIMTAM routine.

X-ray Photoelectron Spectroscopy of Fast-Frozen Hematite Colloids in Aqueous Solutions. 2. Tracing the Relationship between Surface Charge and Electrolyte Adsorption

Colloidal-sized hematite spheroids exposed to aqueous NaCl solutions were investigated by X-ray photoelectron spectroscopy using the fast-frozen technique. The O1s region provided evidence for (de)protonation reactions of surface (hydr)oxo groups of OH-enriched/O-depleted hematite surfaces. These results were also correlated to changes in sodium (Na 1s) and chloride (Cl 2p) contents with pH. Electrolyte ion surface loadings were successfully predicted using a classic thermodynamic adsorption model normalized for surface site density. These efforts pointed to ion-specific inner-Helmholtz plane capacitances.

Accurate correlation, thermochemistry, and structural interpretation of equilibrium adsorption isotherms of water vapor in zeolite 3A by means of a generalized statistical thermodynamic adsorption model

Due to its low energy consumption and ease of operation, the zeolite 3A molecular-sieve pressure-swing adsorption process is currently becoming the method of choice for the production of fuel ethanol worldwide. Accurate correlation of the equilibrium adsorption isotherms of water vapor in zeolite 3A is required for the reliable modeling and simulation of that process. In this paper, we firstly show that popular adsorption isotherm models such as those of Langmuir, Sips, Toth, UNILAN, and Dubinin–Astakhov are uncapable of correlating the available equilibrium adsorption isotherms of water vapor in zeolite 3A. Hill's statistical thermodynamic adsorption model, which was originally expressed in terms of absolute activities and canonical partition functions for sites with a variable number of molecules adsorbed, is rewritten here in terms of the pressure and a set of temperature-dependent adjustable parameters that turn out to correspond to the equilibrium constants of adsorption in those sites. In contrast to other recast versions of Hill's model, our version does neither parameterize nor decouple the canonical partition functions or the configurational integrals, and can be applied to the adsorption of either non-polar or polar molecules. Our generalized model allows not only an easier interpretation of the isotherms fit but also the prediction of thermochemical quantities such as the differential and integral heats of adsorption. From the application of our generalized model, we obtain a very accurate correlation of the available equilibrium adsorption isotherms of water vapor in zeolite 3A in the temperature range from 0 to 100 °C. We also provide thermochemical and structural interpretations of the isotherms fit and made predictions for the isosteric heat of adsorption and the integral heat of immersion that are in excellent agreement with the experimental data.

Charge Localization in Cation−Sulfate Complexes: Implications for Thermodynamic Surface Complexation Models of the Mineral/Water Interface

The applicability of separating charges of oxyanions across inner- and outer-Helmholtz planes according to the charge distribution model was tested by investigating the theoretical charge distribution in 13 metal−sulfate complexes (Be2+, Mg2+, Ca2+, Sr2+, Ba2+, Co2+, Ni2+, Cu2+, Zn2+, Pd2+, Cd2+, Al3+, and Ga3+) using the methods of atoms in molecules and of the electron localization function. Density functional theory gas-phase geometry optimization calculations revealed that unbound oxygens of the sulfate molecules contracted to relatively constant S−O bond lengths of 1.432 ± 0.019 (3 σ) Å irrespective of the bond strength with the metal ions. The populations of the valence basins of the unbound oxygens also remained relatively constant, showing that even the strongest complexation induces very little charge distribution across the sulfate molecule. Maps of the Laplacian of the electron density and of the electron localization function revealed that although charge is relatively localized at the oxygen centers, there is no clear charge separation between the inner- and outer-Helmholtz planes. Thermodynamic adsorption models that avoid subtle distributions of charge across static adsorption planes are suggested to represent a more natural expression of the interface. Models that could instead simulate the changes in the charge-storage capacity of the interface via changes in the capacitance caused by strongly adsorbing molecules are suggested as future alternatives to current-day approaches. It should nonetheless be emphasized that the charge distribution model remains a valuable approach and should have the best applicability at low surface loadings and with molecules with sizes similar or larger to those of the compact layer.

General Relationships of the Adsorption Behavior of Surfactants at the Water/Air Interface

The structure of a surfactant is in direct correlation with the properties of an adsorption layer formed at a liquid interface. By use of thermodynamic adsorption models, such as the Frumkin, reori...

Soil pore surface properties in managed grasslands

Properties of pore surfaces control adsorption and transport of water and chemicals in soils. Parameters are needed to recognize and monitor changes in pore surfaces caused by differences in soil management. Data on gas adsorption in soils can be compressed into parameters characterizing (a) area available to a particular adsorbate, and (b) surface roughness or irregularity. Our objectives were to see (a) whether models of adsorption on fractal surfaces are applicable to water vapor adsorption in soils in the capillary condensation range, and (b) whether differences in long-term management of grasslands are reflected by soil pore surface properties. Water vapor adsorption was measured in Gray Forest soil (Udic Argiboroll, Orthic Greyezem, clay loam) samples taken at four plots, where a long-term experiment on grassing arable land had been carried out for 12 years. The experiment had 2×2 design. Factors were ‘harvest–no-harvest’ and ‘fertilizer–no-fertilizer’. The hay was cut after over-seeding in harvested treatments every year. Ammonium nitrate, superphosphate, and potassium chloride were applied annually after the snowmelt to get the total amount of nutrients of 60 kg ha −1. The monolayer adsorption capacity was estimated from the Brunauer–Emmett–Teller model. A fractal Frenkel–Halsey–Hill model of adsorption on a fractal surface, and a thermodynamic adsorption model were applied in the range of relative pressures from 0.7 to 0.98 and provided good fit of data. Values of the surface fractal dimension D s were in the range from 2.75 to 2.85. Removal of carbohydrates resulted in increase of D s. Differences in management practices did not affect values of D s in the scale range studied, whereas the monolayer capacity was affected. Both fertilization and harvesting resulted in an increase of the monolayer capacity, with the largest increase observed in soil that was fertilized but not harvested.

Thermodynamic and Micromechanical Approaches to the Adhesion between Polyethylene Terephthalate and Silicon Oxide

The adhesion between different types of polyethylene terephthalate (PET) substrates coated with thin silicon oxide (SiO x ) layers is examined using two alternative approaches. The surface of the polymer was hydrolyzed or silylated prior to the deposition of the oxide layer, to be compared with untreated PET. The first approach is the thermodynamic adsorption model from which are defined the dispersive and polar components of the polymer surface energy, obtained from wetting measurements. The second approach is the micromechanical analysis of the interface stress transfer which provides the interface shear strength from the measurement of the density of coating cracks vs. applied tensile strain. The hydrolysis treatment slightly hydrophobizes the PET surface; however, it does not significantly modify the interface shear strength compared with the untreated material. By contrast, the silane treatment improves the polar component of the PET, which is related, to a first approximation, to the measured 30% increase of the interface shear strength compared to the untreated material.

A Critical Comparison of Adsorption Models for Soluble Surfactants

The adsorption isotherm of a soluble anionic surfactant was measured and discussed within the framework of established thermodynamical models. The adsorbed amount derived by these models was compared with the results obtained by second harmonic generation, SHG. SHG can be used as a highly surface specific probe which allows the determination of orientation and number density. Since no thermodynamic quantities are involved in the interpretation of SHG measurements, the data can be used to assess the validity and underlying assumptions of thermodynamic adsorption models. The SHG experiments reveal a good agreement with the Frumkin model. No indication of a subsurface layer can be found.

Adsorption Study of 47 Elements on Alumina and Bentonite Using a Multitracer Technique

Uranyl nitrate, UO2(NO3)2, was irradiated with a 25 MeV/nucleon 40Ar ion beam, and the target material removed by means of solvent extraction. A radioactive multitracer solution containing 47 elements and 83 nuclides free from carriers was thereby prepared. The multitracer solution was used in an adsorption study of 47 elements on alumina and bentonite. The distribution coefficients (Kd) of the 47 elements were simultaneously determined and correlated with the electron binding energy (Iz), and explained by the thermodynamic model for adsorption of James and Healy (1972).

High-pressure Methane Adsorption on Natural and Synthetic Zeolites

The adsorption isotherms of methane on synthetic (5A and 13X) and natural (Erionite) zeolites at different temperatures have been obtained through the use of a high-pressure volumetric adsorption apparatus over the pressure range 0–5 MPa. The isotherms have been analyzed on the basis of a statistical thermodynamic adsorption model, variation in the temperature allowing calculation of the isosteric heat of adsorption. The results show that these zeolites are highly efficient for methane storage at moderately low pressure (0.5–1 MPa).