Surface Excess Adsorption Research Articles

Adsorption of N 2, CH 4, CO and CO 2 gases in single walled carbon nanotubes: A combined experimental and Monte Carlo molecular simulation study

In this study, the adsorption capacity of single-wall carbon nanotubes (SWCNTs) bundles with regard to the pure CH 4, N 2, CO and CO 2 gases at 298 K and pressure range from 0.01 up to 2.0 MPa has been investigated experimentally and computationally. Experimental work refers to gravimetric surface excess adsorption measurements of each gas studied in this nanomaterial. Commercial samples of pristine SWCNTs, systematically prepared and characterized at first, were used for the evaluation of their adsorption capacity. A Langmuir type equation was adopted to estimate the total adsorption isotherm based on the experimental surface excess adsorption data for each system studied. Computational work refers to Monte Carlo (MC) simulation of each adsorbed gas on a SWCNTs model of the type (9, 9) in the grand canonical (GC) ensemble at the same conditions with experiment using Scienomics’ MAPS platform software simulation packages such as Towhee. The GCMC simulation technique was employed to obtain the uptake wt% of each adsorbed gas by considering a SWCNTs model of arrays with parallel tubes exhibiting open-ended cylindrical structures as in experiment. Both experimental and simulation adsorption data concerning these gases within the examined carbon material are presented and discussed in terms of the adsorbate fluid molecular characteristics and corresponding interactions among adsorbate species and adsorbent material. The adsorption isotherms obtained exhibited type I (Langmuir) behavior, providing enhanced gas–substrate interactions. We found that both the experimental as well as the simulated adsorption uptake of the examined SWCNTs at these conditions with regard to the aforementioned fluids and in comparison with adsorbate H 2 on the same material increase similarly and in the following order: H 2 ≪ N 2 ≈ CH 4 < CO ≪ CO 2. Furthermore, for each adsorbate fluid the calculations exhibit somewhat greater gas uptake with pressure compared to the corresponding experiment. The difference in the absolute uptake values between experiment and simulation has been discussed and ascribed to the following implicit factors: (i) to the employed model calculations, (ii) to the remained carbonaceous impurities in the sample, and (iii) to a proportion of close ended tubes, contained in the experimental sample even after preparation.

High pressure adsorption of hydrogen, nitrogen, carbon dioxide and methane on the metal–organic framework HKUST-1

High pressure adsorption phenomena are discussed for different gases on HKUST-1 (Cu 3(BTC) 2, commercially available product Basolite TM C300). Sorption isotherms for hydrogen, nitrogen, methane and carbon dioxide on HKUST-1 were measured in the temperature range of 273–343 K and at pressures up to 50 MPa. The calculated surface excess adsorption capacities for all four adsorptive are one of the highest reported in the literature for HKUST-1 samples. All surface excess data were further calculated from the experimental data by using the helium buoyancy correction. A detailed description was given. Also a procedure to calculate the absolute amount adsorbed from the surface excess amount by using two different models is shown. Using one model, the density and the volume of the adsorbed phase can be calculated. The density of the adsorbed phase ρ ads corresponds to the liquid density of the adsorptive at its boiling point ρ liq,BP. In case of hydrogen no excess maximum was found up to 50 MPa, so that one model could not be applied. Finally, the isosteric heat of adsorption for each gas was calculated by using the Clausius–Clapeyron equation.

Density functional approach for modeling CO2 pressurized polymer thin films in equilibrium

We have used polymer density functional theory to analyze the equilibrium density profiles and interfacial properties of thin films of polymer in the presence of CO(2). Surface tension, surface excess adsorption of CO(2) on polymer surface, and width of the interface are discussed. We have shown the changes in these properties in the presence of CO(2) and with increasing film thickness and their inverse linear relationship with increasing chain length. One of our important findings is the evidence of segregation of end segments toward the interface. We have introduced a new method of representing this phenomenon by means of Delta profiles that show increase in segregation owing to the presence of CO(2) and with increasing chain length. We also make predictions for the octacosane-CO(2) binary system near the critical point of CO(2). Our results indicate qualitative trends that are comparable to the similar experimental and simulation studies.

Surface tension and adsorption of electrolytes at the aqueous solution-gas interface

The surface tension of aqueous solutions of hydrogen, sodium, and potassium chlorides was measured. The excess adsorption isotherms for electrolyte adsorption at the liquid-gas interface were obtained. The dependence of the surface tension on the solute concentration exhibits an extremal character, with the onset surface-inactivity of electrolytes being observed at concentrations above 0.3 M. The composition of the surface layer was demonstrated to be governed by the energy of solvation, while the extrema in the surface tension and excess adsorption isotherms are associated with the behavior of individual ions in the adsorption layer of the interphase interface.

Recovery of Linamarin by Adsorption of Cassava Extract onto Activated Carbon

The unavailability of linamarin and its use in various applications such as determining the cyanide content in cassava flour and chips and measuring glucose in biomedical applications and hydrogen cyanide in the environment using linanmarin/linamarase/SnO2 electrode biosensors have necessitated its recovery from cassava tissues. A 0.2 μm membrane was used at a filtration rate of 1.44 mL/min for the initial isolation of linamarin, followed by extract adsorption onto activated carbon. U-shaped isotherms were observed for the adsorption of bulk cassava jelly-like solid (BJS) extract onto activated carbon. The phenomenon can be described by the selective adsorption of the solvent (B) while the solute (A) is left concentrated, resulting in an initial increase in A until equilibrium is reached and A starts to drop. This process in which the concentration of the solute in the presence of the solvent results from competitive adsorption (solute−solvent) is referred to as surface excess adsorption. Integration of the results from both 1H NMR and IR analyses indicates that the product was linamarin. The decomposition temperature of the purified product was found to be in the range of 138−140 °C, which corresponds to values reported in the literature. The Freundlich empirical adsorption equation was used to simulate surface excess adsorption where values of the volume of solute per mass adsorbed (v) at 25 and 65 °C were found to be 0.434 and 3.950 mL/g, respectively. In comparison, the values calculated using the Freundlich equation fitted the experimental data quite well.

Thermodynamics of adsorption of binary aqueous organic liquid mixtures on a RPLC adsorbent

The surface excess adsorption isotherms of organic solvents commonly used in RPLC with water as co-eluent or organic modifiers (methanol, ethanol, 2-propanol, acetonitrile and tetrahydrofuran) were measured on a porous silica surface derivatized with chlorotrimethylsilane (C 1-silica with 3.92 μ mol C 1 groups per m 2 of SiO 2), using the dynamic minor disturbance method. The 5 μ m diameter particles were packed in a 150 mm × 4.6 mm column. The isotherm data were derived from signals resulting from small perturbations of the equilibrium between the aqueous–organic solutions and the adsorbent surface. The partial molar surface area of the adsorbed components were assumed to be the same as those of the pure components. The difference σ − σ i ∗ between the surface tensions of the adsorbed mixtures and that of the pure liquids was measured as a function of the organic modifier molar fraction. A simple and unique convention for the position of the Gibbs dividing surface was proposed to delimit the Gibbs’s adsorbed phase and the bulk liquid phase. The activity coefficients of the organic modifiers and of water and their thermodynamic equilibrium constants between the two phases were measured. The strong non-ideal behavior of the adsorbed phase is mostly accounted for by the surface heterogeneity. Some regions of the surface (bonded –Si(CH 3) 3 moieties) preferentially adsorb the organic compound while the regions close to unreacted silanols preferentially adsorb water.

A new generalization of the Carnahan-Starling equation of state to additive mixtures of hard spheres

We introduce an expansion of the equation of state for additive hard-sphere mixtures in powers of the total packing fraction with coefficients which depend on a set of weighted densities used in scaled particle theory and fundamental measure theory. We demand that the mixture equation of state recovers the quasiexact Carnahan-Starling [J. Chem. Phys. 51, 635 (1969)] result in the case of a one-component fluid and show from thermodynamic considerations and consistency with an exact scaled particle relation that the first and second orders of the expansion lead unambiguously to the Boublik-Mansoori-Carnahan-Starling-Leland [J. Chem. Phys. 53, 471 (1970); J. Chem. Phys. 54, 1523 (1971)] equation and the extended Carnahan-Starling equation introduced by Santos et al. [Mol. Phys. 96, 1 (1999)]. In the third order of the expansion, our approach allows us to define a new equation of state for hard-sphere mixtures which we find to be more accurate than the former equations when compared to available computer simulation data for binary and ternary mixtures. Using the new mixture equation of state, we calculate expressions for the surface tension and excess adsorption of the one-component fluid at a planar hard wall and compare its predictions to available simulation data.

Thermodynamically Consistent Adaptation of Scaled Particle Theory to an Arbitrary Hard-Sphere Equation of State

Scaled particle theory (SPT) is adapted to an arbitrary hard-sphere equation of state (EOS) while utilizing an SPT interpolation function that satisfies all the exact conditions of SPT and, as such, is thermodynamically consistent. The new modification of SPT is tailored to predict with high accuracy the reversible work of forming a cavity in a hard-sphere fluid, but it also estimates the surface tension and excess surface adsorption. The application of additional SPT conditions also provides estimates of the first two derivatives of the hard-sphere radial distribution function (RDF) at contact. When various accurate equations of state are used, in particular, the Carnahan−Starling EOS, the resulting work of cavity formation is nearly identical to accurate Monte Carlo simulation data and the predictions of the recent SPT6 [Heying and Corti, J. Phys. Chem. B 2004, 108, 19756]. The estimates of the surface tension and surface adsorption at moderate to high packing fractions deviate somewhat from both previous theoretical techniques and the simulation. Meanwhile, EOS-based predictions of the initial slope of the RDF are very close to simulation estimates. Predictions of the initial curvature, like those of SPT6, deviate from simulation, but not drastically so. The overall accuracy of our version of SPT demonstrates that a thermodynamically consistent modification of SPT provides correct predictions of the work of cavity formation and is, therefore, suitable for use as the ideally repulsive reference state in various solvation theories of liquids.

Preferential solubilization of dodecanol from dodecanol–limonene binary oil mixture in sodium dihexyl sulfosuccinate microemulsions: Effect on optimum salinity and oil solubilization capacity

Solubilization of dodecanol–limonene binary oil mixtures has been studied in saturated Winsor type I and III sodium dihexyl sulfosuccinate microemulsions. The systems showed different oil solubilization behavior below and above dodecanol volume fraction 0.2. Below 0.2 dodecanol volume fraction regular Winsor type microemulsions formed. The oil solubilization was characterized in this concentration range by the optimum salinity and the maximum characteristic length. Dodecanol showed Langmuirian-type surface excess adsorption at the vicinity of the surfactant layer. Variation of the optimum salinity and middle phase characteristic length with increasing dodecanol concentration could be linked to changes in the dodecanol surface excess. These relationships were used to develop new mathematical models for the optimum salinity and characteristic length as a function of oil phase composition. Both models yield excellent agreement with the data. Above dodecanol volume fraction 0.2 regular Winsor type III microemulsions are not formed. Therefore our new models are not applicable in this concentration range.

04/02670 Reduced ductility of in-service 9Cr1Mo piping revealed during welding procedure qualification: Gray, G. M. and Croker, A. B. L. International Journal of PressureVessels and Piping, 2004, 81, (6), 543–555

Frothers are surface active molecules and facilitate to produce more mechanically stable froth by reducing the surface tension at air–water interface. It adsorbs at the air–water interface and serves to reduce the loss of water from the lamellae of bubble. In this investigation weak and powerful frothers, like methyl isobutyl carbinol (MIBC) and polyethylene glycol-600 (PEG) were used for studying the surface tension of frother blends at various concentrations. Gibb's surface excess adsorption and surface area were determined from the rate of change of surface tension with logarithm of concentration. The high surface area per molecule of PEG signifies that little amount is enough to significantly reduce the interfacial tension at the air–water interface. The foam volume and its stability were measured for single frothers and their blend. The foam stability (foaminess) of single MIBC is very less however; it could be improved significantly using a small amount of strong frother (PEG).Flotation studies of coal fines from eastern part of India were carried out with the above two types of frothers and their blend. The performances were compared with reference to recovery of combustibles for clean coal and rejects. It was found that coal concentrate contains high ash with single PEG due to high froth stability that results the entrainment of the gangues, while single MIBC produces high grade concentrate with low recovery. It was observed that the recovery of carbon value increases significantly when a 10% (w/w) of powerful frother was added with MIBC. The recovery of carbon at 90:10 ratio of frother blend is 77.6% at 17% ash. The recovery could be increased to 86% when ash in clean coal increases to 19.7% and loss of combustibles in the tailing could also be reduced to 14%.

The influence of association of alcohol molecules on their adsorption and desorption heats

The paper presents the results of calorimetric measurements and surface excess adsorption isotherms for adsorption process of n-butanol from n-hexane on controlled porosity glasses of different mean pore diameters. The pore diameter was found to have very small effect on the adsorption heat, while it affects the desorption heat recorded by the flow microcalorimeter. Moreover, in the region of very low alcohol concentration in solution, the heat of adsorption exhibits sharp maximum for both narrow and wide pore diameters. This rather puzzling result is attributed to the effect of molecular association of alcohol molecules in the solution.

Adsorption of 1-heptanol on bismuth single-crystal plane electrodes

Cyclic voltammetry, impedance and chronocoulometry have been employed for the quantitative study of 1-heptanol (1-HepOH) adsorption on the bismuth single-crystal plane|aqueous Na2SO4 solution interface. The adsorption isotherms, Gibbs energies of adsorption, $$ \Delta G_{\rm A}^ {\circ} $$ , the limiting surface excess, Γmax, and other adsorption parameters have been determined. The adsorption of 1-HepOH on Bi single-crystal planes is mainly physical and is limited by the rate of diffusion of organic molecules to the electrode surface. Comparison of the adsorption data for 1-HepOH with other alcohols shows that the adsorption characteristics depend on the structure of the hydrocarbon chain. The adsorption activity of adsorbates at the bismuth|solution interface increases in the sequence 1-propanol<1-butanol<1-pentanol<1-hexanol<1-heptanol as the adsorption activity at the air|solution interface increases. For all the compounds studied, the adsorption activity increases in the sequence of planes as $$ (111) < (001) < (01\overline 1 ) $$ .

Effects of surface nonuniformity and molecular association on mechanism of butanol adsorption from solution

The paper presents the results of calorimetric measurements and surface excess adsorption isotherms for n-butanol adsorption from n-hexane on a series of controlled porosity glasses characterized by different mean pore diameters. It is demonstrated that, in the region of very low alcohol concentration in solution, the heat of adsorption exhibits sharp maximum, independently of the pore diameter of adsorbent. This rather puzzling result is explained by the heterogeneity of the surface and the effects of molecular association of alcohol molecules in the solution. A simple theoretical model that supports our predictions is presented.

Comparative Study on Physical Adsorption of Vapor and Supercritical H 2 and Ch 4 on Swnh and Acf

Adsorption isotherms of H 2 and CH 4 on activated carbon fibers (ACF) and single-walled carbon nanohorns (SWNH) were measured at vapor and supercritical conditions. H 2 and CH 4 are adsorbed sufficiently on micropores of ACF and SWNH at the vapor conditions and their adsorption isotherms were described by the Dubinin-Radushkevich equation. This shows clearly that even adsorption of H 2 and CH 4 vapors can be described by micropore filling mechanism. However, the adsorption isotherms of supercritical H 2 and CH 4 sensitively depend on the measuring temperature; the higher the measuring temperature, the smaller the amount of adsorption. Although H 2 adsorption isotherm of SWNH at 77 K is of type I and the maximum surface excess adsorption is 0.7 wt.% at 5 MPa, the adsorption isotherm was of Henry type at 300 K and the adsorption amount is less than 0.1 wt.% at 5 MPa.

Theory of Size Dependent Deliquescence of Nanoparticles: Relation to Heterogeneous Nucleation and Comparison with Experiments

In this paper, we develop a thermodynamic theory for the deliquescence behavior of soluble crystals in an atmosphere of solvent vapor. In this endeavor, we have focused on studying possible free energy barriers that could impede deliquescence. Our aim was to construct a theory general enough to treat both macroscopic and nanosized crystals. Toward this end, as a first attempt, we focused on a theory capable of describing the qualitative features of the results of recent experimental measurements, especially in the nanometer range where interfacial effects are bound to play a role. However, we have also opted for simplicity, and with this in mind, the surface thermodynamics that we have used are of the simplest type, ignoring crystal shape, rigorously defined dividing surfaces, curvature dependence of surface tension, and the presence of surface excess (adsorption). We do however include the effects of “disjoining pressure”. Nevertheless, we are able to describe several of the observed features and to calc...

A new determination method of absolute adsorption isotherm of supercritical gases under high pressure with a special relevance to density-functional theory study

A new determination method of an absolute adsorbed amount nab from the surface excess mass nex for high-pressure adsorption isotherms of a supercritical gas was proposed. The effectiveness of new method was examined by using the density-functional theory (DFT). The DFT study showed that this analysis can provide reasonable results; both of the absolute adsorbed amount determined from the proposed method and the DFT agreed within 5% at 90 MPa and only 1% below 5 MPa. Furthermore, we applied this new method to the experimental surface excess isotherm in the literature, which has a maximum. The analyzed absolute adsorption isotherm from the surface excess adsorption isotherm having a maximum were of IUPAC type I or type II. This method gave the thickness of the interfacial layer of the adsorbed phase.

Adsorption of critical and supercritical fluids

We develop a crossover theory for critical adsorption of pure fluids in a semi-infinite system. In our previous publication [Phys. Lett. A 251, 212 (1999)] we applied the theory to the analysis of experimental data for adsorption of liquid SF6 on the critical isochore only. In this article we extend the theory on the noncritical isochores and present a comparison of the theoretical predictions for the surface excess (Gibbs) adsorption with experimental data for CO2/silica and SF6/graphite systems. Good representation of experimental data is achieved in the range of temperatures from the saturated temperature up to 1.15 Tc and densities 0.5ρc⩽ρ⩽1.5ρc. The optimization of the model to the excess isotherms in both systems indicates that they have surface critical behavior in the universality class of normal transition. However, in this case model does not reproduce the excess adsorption data for SF6/graphite system at temperatures τ=T/Tc−1⩽0.02 at ρ=ρc. Analysis of the excess adsorption data along the critical isochore in SF6/graphite system indicates that the surface field h1 vanishes linearly with τ as T→Tc, which corresponds to the ordinary transition.

98/00084 Sulphur distribution in Illinois No. 6 coal subjected to different oxidation pre-treatments

Frothers are surface active molecules and facilitate to produce more mechanically stable froth by reducing the surface tension at air–water interface. It adsorbs at the air–water interface and serves to reduce the loss of water from the lamellae of bubble. In this investigation weak and powerful frothers, like methyl isobutyl carbinol (MIBC) and polyethylene glycol-600 (PEG) were used for studying the surface tension of frother blends at various concentrations. Gibb's surface excess adsorption and surface area were determined from the rate of change of surface tension with logarithm of concentration. The high surface area per molecule of PEG signifies that little amount is enough to significantly reduce the interfacial tension at the air–water interface. The foam volume and its stability were measured for single frothers and their blend. The foam stability (foaminess) of single MIBC is very less however; it could be improved significantly using a small amount of strong frother (PEG).Flotation studies of coal fines from eastern part of India were carried out with the above two types of frothers and their blend. The performances were compared with reference to recovery of combustibles for clean coal and rejects. It was found that coal concentrate contains high ash with single PEG due to high froth stability that results the entrainment of the gangues, while single MIBC produces high grade concentrate with low recovery. It was observed that the recovery of carbon value increases significantly when a 10% (w/w) of powerful frother was added with MIBC. The recovery of carbon at 90:10 ratio of frother blend is 77.6% at 17% ash. The recovery could be increased to 86% when ash in clean coal increases to 19.7% and loss of combustibles in the tailing could also be reduced to 14%.

Impact of molecular structure on the performance of methyl ester ethoxylates

AbstractMethyl ester ethoxylates are a new class of ethylene oxide (EO)‐derived surfactants. Little is known about the impact of structural variations on their performance properties. The effects of carbon chain length, EO content, the degree of unsaturation of the methyl ester feedstock, and feedstock purity were examined for their impact on both physical properties and surfactant performance properties. Physical properties examined included surface properties (surface tension, critical micelle concentration, surface excess adsorption), melting point, water solubility, viscosity, foam stability, color, clarity, and odor. The impact of molecular structure on performance was examined for various applications, including laundry detergents, dishwashing detergents, and hard‐surface cleaners.

98/00083 Structural changes induced by thermal treatment of deashed coals

Frothers are surface active molecules and facilitate to produce more mechanically stable froth by reducing the surface tension at air–water interface. It adsorbs at the air–water interface and serves to reduce the loss of water from the lamellae of bubble. In this investigation weak and powerful frothers, like methyl isobutyl carbinol (MIBC) and polyethylene glycol-600 (PEG) were used for studying the surface tension of frother blends at various concentrations. Gibb's surface excess adsorption and surface area were determined from the rate of change of surface tension with logarithm of concentration. The high surface area per molecule of PEG signifies that little amount is enough to significantly reduce the interfacial tension at the air–water interface. The foam volume and its stability were measured for single frothers and their blend. The foam stability (foaminess) of single MIBC is very less however; it could be improved significantly using a small amount of strong frother (PEG).Flotation studies of coal fines from eastern part of India were carried out with the above two types of frothers and their blend. The performances were compared with reference to recovery of combustibles for clean coal and rejects. It was found that coal concentrate contains high ash with single PEG due to high froth stability that results the entrainment of the gangues, while single MIBC produces high grade concentrate with low recovery. It was observed that the recovery of carbon value increases significantly when a 10% (w/w) of powerful frother was added with MIBC. The recovery of carbon at 90:10 ratio of frother blend is 77.6% at 17% ash. The recovery could be increased to 86% when ash in clean coal increases to 19.7% and loss of combustibles in the tailing could also be reduced to 14%.