Surface Free Energy Of Adsorption Research Articles

Effect of amino functional groups on the surface properties and Lewis's acid base parameters of UiO-66(NH2) by inverse gas chromatography

Amino-functionalized metal organic frameworks (MOFs) have attracted much attention for various applications such as carbon dioxide capture, water remediation and catalysis. The focus of this study is to determine the surface and Lewis's acid-base properties of UiO-66(NH2) crystals by the inverse gas chromatography (IGC) technique at infinite dilution. The latter was applied to evaluate the dispersive component of the surface energy γsd(T) by using thermal model and several molecular models. The obtained results proved that γsd(T) decreases when the temperature increases. The best results were achieved by using the thermal model that takes into account the effect of the temperature on the surface areas of the organic molecules. We also observed a decrease of the Gibbs surface free energy of adsorption by increasing the temperature of the different organic solvents. The polar interactions of UiO-66(NH2) were obtained by using the methods of Saint-Flour Papirer, Donnet et al., Brendlé-Papirer and the different molecular models. The Lewis's acid base constants KA and KD were further calculated by determining the different variables of adsorption of the probes on the solid surface and the obtained values were 1.07 and 0.45 for KA and KD respectively, with an acid-base ratio (KA/KD) of 2.38. These values showed the high acidic surface of the solid substrate; whereas, the values of the entropic acid base parameters, ωA, ωD and ωA/ωD respectively equal to 1.0×10−3, 3.8×10−4 and 2.73, also highlighted the important acidity of UiO-66-(NH2) surface. These important findings suggest that the surface defects (missing linkers and/or clusters) in UiO-66(NH2) are the main determining factor of the acid-base properties of UiO-66 based structures.

Surface tension of polytetrafluoroethylene and its wetting by aqueous solution of some surfactants and their mixtures

Measurements of the contact angle of aqueous solution of rhamnolipid (RL) mixture with n-octyl-β-d-glucopyranoside (OGP), Triton X-100 (TX-100) or/and sodium dodecylsulfate (SDDS) on polytetrafluoroethylene (PTFE) were made. To this aim there was used a plate whose surface topography was analyzed by means of optical profilometry method. Additionally, plate surface chemistry was studied employing the Fourier transform infrared spectroscopy. The obtained values of contact angle were discussed based on the PTFE surface tension (γSV) as well as the Lifshitz-van der Waals component of the water surface tension (γWLW). The contact angle of aqueous solution of several surfactants and their mixtures on PTFE was also considered on the basis of γSV and γWLW. It occured that by using the values of γSV, γWLW and surface tension of the aqueous solution of surfactants and their mixtures, the contact angle on PTFE can be predicted. It also occured that changes of adhesion tension of aqueous solutions of surfactants as a function of their concentration can be determined by the exponential function of the first or second order. Using such functions Gibbs surface excess concentration of surfactants at the PTFE-water interface, mole fraction of surfactant in the mixed monolayer and fraction of the area occupied by given surfactants in the monolayer were determined. Gibbs surface free energy of adsorption of a given surfactant in the presence of another one and adhesion work of the aqueous solution of surfactants to the PTFE surface were also evaluated.

Surface and volumetric properties of n-octyl-β-d-glucopyranoside and rhamnolipid mixture

The measurements of surface tension, density and viscosity of aqueous solutions of n-octyl-β-d-glucopyranoside (OGP) and rhamnolipid (RL) were performed at constant concentration of OGP or RL. The measured values of the surface tension were compared to those calculated from the Joos equation as well as to the hypothetical one. The obtained results were analyzed with regard to adsorption at the water-air interface and micellization of OGP in the presence of RL and vice versa. On the basis of this analysis, the Gibbs surface excess concentration of the particular surfactants at the water-air interface, the Gibbs surface free energy of adsorption and micellization, the composition of the surface layer, the apparent and partial molar volumes of OGP and RL were determined. The Gibbs surface free energy of adsorption was calculated on the basis of the critical micelle concentration (CMC) and the surface tension values at this concentration as well as by using the Langmuir equation. The composition of the surface layer was compared to that of hypothetical one. In turn, apparent and partial molar volumes were discussed in the light of the volume of surfactant molecules on the basis of the length and angle of the bonds. From the obtained results it was deduced that there is a strong synergism in the reduction of water surface tension by the OGP and RL mixture as well as in the CMC. The adsorption of RL increases in the presence of OGP but OGP decreases in the presence of RL.

Influence of short chain alcohols on adsorption of sodium dodecylsulfate and Triton X-100 mixture at solution–air interface

Measurements of the surface tension of the aqueous solutions of sodium dodecylsulfate (SDDS) and p-(1,1,3,3-tetramethylbutyl)phenoxypoly(ethylene glycol) (Triton X-100 or TX-100) mixture with methanol, ethanol or propanol were carried out in the whole range of alcohol concentration and in the range of the surfactant mixture concentration from 1×10−5 to 5×10−3M. On the basis of the obtained results the surface excess concentration of the surfactant mixture and alcohol was determined and compared to the surface excess concentration of the particular components of the solution. Taking into account the values of the surface excess concentration of the surfactant mixture and alcohol obtained on the basis of the surface tension values of the aqueous solutions of the TX-100 and SDDS mixture with alcohol as well as the surface excess concentration of individual TX-100, SDDS and alcohol from their aqueous solutions, the mutual influence of the surfactant mixture and alcohol on their adsorption at the solution–air interface was considered. Therefore the alcohol activity at the solution–air interface was calculated by using the Sprow and Prausnitz equation. The mutual behavior of TX-100 and SDDS in the presence of alcohol was determined on the basis of Rosen's theory of regular solutions. The influence of the particular components of the water+alcohol solutions of the TX-100 and SDDS mixture was discussed in the light of the Gibbs surface free energy of adsorption of these components at the solution–air interface. This energy was determined by different methods and it appeared that the equation of Gu and Zhu proposed for the surfactant adsorption at the solid–solution interface was also useful for determination of the standard free energy of adsorption of alcohols at the solution–air interface.

Sulfate Adsorption at the Buried Fluorite–Solution Interface Revealed by Vibrational Sum Frequency Generation Spectroscopy

Understanding the structure and energetics of adsorbed ions at buried mineral/solution interfaces has great importance to the geochemical and atmospheric chemistry communities. Vibrational spectroscopy is a powerful tool for the study of mineral/solution interfaces as these techniques can be applied in situ, are sensitive to surface structures, and are generally nondestructive. The use of vibrational sum frequency generation spectroscopy (VSFG), which is inherently interface-specific, is applied here to study the adsorption of sulfate at the buried fluorite (CaF2)/Na2SO4 solution surface at pH 7 and 298 K in the presence of an aqueous background electrolyte, NaCl. The use of VSFG allowed for the resolution of adsorbed sulfate complexes from sulfate molecules which reside in the interfacial electric double layer yet remain fully solvated. The sulfate anion is found to adsorb with a bidentate inner-sphere structure at the fluorite surface with an average surface free energy of adsorption of −31 ± 3 kJ/mol f...

Characterization of the surface properties of nitrogen-enriched carbons by inverse gas chromatography methods

The characterization of the surface properties of carbonaceous materials by inverse gas chromatography (IGC) techniques is described. The cokes investigated were produced by the co-pyrolysis of a coal-tar pitch (CTP) with different amounts of polyacrylonitrile (PAN) as a possible method to synthesize carbonaceous materials enriched in nitrogen. IGC at infinite dilution and LSER (linear solvation energy relationship) techniques were used to determine the physical and chemical surface properties of the cokes. In general, the surface free energy of adsorption is due to both dispersive and specific interactions. The dispersive component of the surface free energy was determined using n-alkane probes. For the specific component, which is primarily due to acid–base interactions, different polar probes were used. The LSER method was applied to improve our understanding of the adsorption process in terms of molecular interactions. We show that, to characterize dispersive interactions using n-alkanes, the LSER and IGC methods are equivalent. On the other hand, with both methods we find that all the samples present acidic and basic characteristics. However, the sensitivity of the LSER method does not allow us to discriminate between the three samples in terms of specific interactions.

Influence of polymorphism on the surface energetics of salmeterol xinafoate crystallized from supercritical fluids.

To characterize the surface thermodynamic properties of two polymorphic forms (I and II) of salmeterol xinafoate (SX) prepared from supercritical fluids and a commercial micronized SX (form 1) sample (MSX). Inverse gas chromatographic analysis was conducted on the SX samples at 30, 40, 50, and 60 degrees C using the following probes at infinite dilution: nonpolar probes (NPs; alkane C5-C9 series); and polar probes (PPs; i.e., dichloromethane, chloroform, acetone, ethyl acetate, diethyl ether, and tetrahydrofuran). Surface thermodynamic parameters of adsorption and Hansen solubility parameters were calculated from the retention times of the probes. The free energies of adsorption (- deltaG(A)) of the three samples obtained at various temperatures follow this order: SX-II > MSX approximately/= SX-I for the NPs; and SX-II > MSX > SX-I for the PPs. For both NPs and PPs, SX-II exhibits a less negative enthalpy of adsorption (deltaH(A)) and a much less negative entropy of adsorption (ASA) than MSX and SX-I, suggesting that the high -AGA of SX-II is contributed by a considerably reduced entropy loss. The dispersive component of surface free energy (gammas(D)) is the highest for MSX but the lowest for SX-II at all temperatures studied, whereas the specific component of surface free energy of adsorption (-deltaG(A)SP) is higher for SX-II than for SX-I. That SX-II displays the highest -deltaG(A) for the NP but the lowest gammasD of all the SX samples may be explained by the additional -AGA change associated with an increased mobility of the probe molecules on the less stable and more disordered SX-II surface. The acid and base parameters, K(A) and K(D) that were derived from deltaH(A)SP reveal significant differences in the relative acid and base properties among the samples. The calculated Hansen solubility parameters (deltaD, deltap, and deltaH) indicate that the surface of SX-II is the most polar and most energetic of all the three samples in terms of specific interactions (mostly hydrogen bonding). The metastable SX-II polymorph possesses a higher surface free energy, higher surface entropy, and a more polar surface than the stable SX-I polymorph.

Analysis of the Adsorption of Alkanes on High Surface Area Cellulose by Inverse Gas Chromatography

Abstract The adsorption characteristics of alkanes on high surface area cellulose were investigated by inverse gas chromatography. The enthalpy and entropy of adsorption of alkanes on the solvent exchanged cellulose were greater than the values on non-porous cellulose. The difference in the heats of adsorption of alkanes between the non-porous and the solvent exchanged cellulose was greater for larger molecules indicating stronger interaction for the higher alkanes in the pore structure. For n-hexane the differences in enthalpy and entropy of adsorption were 17 kJ/mole and 52 J/mole K, respectively. The London component of the surface free energy of adsorption was 116 mN/m for the solvent exchanged cellulose.