Gibbs Energy Of Adsorption Research Articles

Synthesis and Interfacial Activity of Novel Heterogemini Sulfobetaines in Aqueous Solution.

Three new heterogemini sulfobetaines and their chloride salts were synthesised. The interfacial activities of the obtained chlorides in aqueous solution were studied by equilibrium and dynamic surface tension measurements. The critical micelle concentration, surface excess concentration, minimum area per surfactant molecule and standard Gibbs energy of adsorption as well as micelle lifetime and diffusion coefficient were determined. The adsorption properties and micelle lifetime of these compounds significantly depend on the length of alkyl chain. The critical micelle concentration decreases with increasing chain length of the compounds considered. The values of the diffusion coefficient of N-alkyl-N-methyl-N-(3-sulfopropyl)-6-(N-alkyl-N-methylamino)hexylammonium chloride tend to decrease as the concentration is increased.

Remarkable enhancement in hydrogen storage on free-standing Ti3B and BC3 supported Ti3 clusters

Hydrogen storage capacity of Tin−1B (n = 3–7) clusters is studied and compared with that of the pristine Tin (n = 3–7), using density functional theory (DFT) based calculations. Among these clusters, Ti3B shows the most significant enhancement in the storage capacity by adsorbing 12 H2, out of which three are dissociated and the other nine are stored as di-hydrogen via Kubas-interaction. The best storage in Ti3B is owed to a large charge transfer from Ti to B along with the largest distance of Ti empty d-states above the Fermi level, which is a distinct feature of this particular cluster. Furthermore, the effect of substrates on the storage capacity of Ti3B was assessed by calculating the number of adsorbed H2 on Ti3 cluster anchored onto B atoms in the B-doped graphene, BC3, and BN substrates. Similar to free-standing Ti3B, Ti3 anchored onto boron atom in BC3, stores nine di-hydrogen via Kubas interaction, at the same time eliminating the total number of non-useful dissociated hydrogen. Gibbs energy of adsorption as a function of H2 partial pressure, indicated that at 250 K and 300 K the di-hydrogens on Ti3@BC3 adsorb and desorb at ambient pressures. Importantly, Ti3@BC3 avoids the clustering, hence meeting the criteria for efficient and reversible hydrogen storage media.

The structural effect of some 1,3,4-oxadiazoles and 1,2,4,5-tetrazines on their thermodynamic characteristics of adsorption from aqueous organic solutions on phenyl-bonded silica gel

The thermodynamic characteristics of adsorption of substituted 1,3,4-oxadiazoles and 1,2,4,5-tetrazines from aqueous organic solutions on phenyl-bonded silica gel were determined in the Henry region via the method of high-performance liquid chromatography. The influence of the structure of the studied compounds on their thermodynamic characteristics of adsorption from binary aqueous organic solvents of different natures was examined. The correlation dependences of the standard differential molar changes in the Gibbs energy, enthalpy, and entropy of adsorption on the van der Waals surface area and reduced dipole moment of molecules of the examined compounds were found. The main factors in optimization of the separation techniques and adjustment of the adsorption selectivity of phenyl-bonded silica gel were determined under conditions of reversed-phase high-performance liquid chromatography.

Equilibrium, kinetics and thermodynamic studies for separation of malic acid on layered double hydroxide (LDH)

The adsorption equilibria of malic acid onto layered double hydroxide (LDH) was studied. In the experimental context of this study, firstly LDH with a highly crystalline structure was synthesized with the co-precipitation method and characterized. In the adsorption experiment some important effects such as, adsorption equilibrium, influence of quantities of LDH as adsorbent, effect of adsorption temperature, and influence of starting concentration of malic acid were investigated. The removal of malic acid was 96.73% the highest percentage for 1g LDH at 298K. The results obtained from the experiment were used to plot Langmuir, Freundlich, and Temkin adsorption isotherms. It has been found that experimental data about solid–liquid equilibria of malic acid with LDH and isotherm equations were appropriate. The equilibrium data show that the adsorption isotherm is compatible with Langmuir isotherm (R2 is 0.9992 at 298K). Adsorption depended on the starting malic acid concentration at various temperatures (298, 308, 318K), respectively. The temperature dependence of adsorption process is associated with changes in several thermodynamic parameters such as standard Gibbs energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) of adsorption and were calculated. Elovich and other kinetic model equations were applied to the obtained data from the experiment.

Thermodynamic study on the interaction of imidazolium salts and POE-type nonionic surfactant in the adsorbed film

The composition of the adsorbed film and the excess Gibbs energy of adsorption $$ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $$ were evaluated from thermodynamic analysis of surface tensions for the 1-decyl-3-methylimidazoulium bromide (C10mimBr)–tetraethylene glycol monooctyl ether (C8E4) and 1-decyl-3-methyl-imidazolium tetrafluorobrorate (C10mimBF4)–C8E4 systems, where the counter anion of imidazolium salts is different from each other. The higher miscibility of two components compared to an ideal mixing and thus negative $$ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $$ were observed in the former, which comes from the ion–dipole interaction between imidazolium cation and the oxyethylene group of C8E4. On the other hand, the lower miscibility and thus positive $$ {\widehat{g}}^{\mathrm{H},\mathrm{E}} $$ were observed for the latter. Such differences were attributed to that BF4 − forms two hydrogen bonds and has stronger affinity with the cationic head group of C10mim+ than Br−. This results in that the ion–dipole interaction between C8E4 and C10mim+ cation is diminished in the C10mimBF4–C8E4 system.

New insight into surface tension inverted curvature for liquid-liquid and solid-liquid binary mixtures: The special case of hexamethylenetetramine in water

Surface tension of most binary liquid systems decreases concavely up with increasing solute concentration. In a lesser extent, surface tension curvature is inverted and decreases concavely down. In this report, inverted curvature is explained through a Modified Extended Langmuir (MEL) isotherm that relates solute bulk concentration and surface coverage through a single lyophobic parameter β, and through the Volmer-Margules (VM) model developed by our group that provides activity coefficients from surface tension data. According to the MEL isotherm, inverted curvature is due to the weak adsorption of the solute at low concentrations, making the surface coverage a concave up function of solute bulk concentration. The MEL model was tested with different liquid-liquid binary mixtures and with the liquid-solid system of water+hexamethylenetetramine (HMT), with partial miscibility hindering its description. The VM model fits HMT surface tension data remarkably well, providing similar activity coefficients to those obtained from isopiestic data. The activity coefficient at infinite dilution of HMT in water is smaller than one, ratifying the weak adsorption of HMT due to its affinity to water in bulk solution. The positive Gibbs adsorption energy computed from the VM model confirms the conclusions, providing a new meaning to the inverted curvature.

Standard Gibbs energy of adsorption and surface properties for ionic liquids binary mixtures

A classical thermodynamic model for the first time is used to derive an equation for the standard Gibbs energy of adsorption and surface properties for ionic liquids binary mixtures. Where experimental surface tension of the mixtures is available, the agreement between the calculated and the experimental data is found to be very good. Bulk mole fraction and surface tension of one of the pure component are necessary inputs for this equation. In addition, to find more information about surface structure of binary mixtures, the surface tension of binary mixtures has been studied using extended Langmuir model (EL).

Determination of the Frumkin and Temkin Adsorption Isotherms of Underpotentially Deposited Hydrogen at Pt Group Metal Interfaces Using the Standard Gibbs Energy of Adsorption and Correlation Constants

At Pt(111), Pt(100), Pt, and Rh interfaces, the Frumkin adsorption isotherm of underpotentially deposited hydrogen (UPD H) and related electrode kinetic data are determined using the standard Gibbs energy of adsorption. The Temkin adsorption isotherm of UPD H correlating with the Frumkin adsorption isotherm of UPD H is readily determined using the correlation constants between the Temkin and Frumkin or Langmuir adsorption isotherms. At the Pt(111), Pt(100), Pt, and Rh interfaces, the lateral repulsive interaction between the UPD H species is interpreted using the interaction parameter for the Frumkin adsorption isotherm. The lateral repulsive interaction between the UPD H species at the Pt(111), Pt(100), Pt, and Rh interfaces is significantly different from the lateral attractive interaction between the overpotentially deposited hydrogen (OPD H) species at Pt, Ir, and Pt-Ir alloy interfaces.

The Effect of Ethanol on Nanostructures of Mixed Cationic and Anionic Surfactants

AbstractMicellization of tetradecyl trimethyl ammonium bromide (TTAB) and sodium dodecyl sulfate (SDS) in water–ethanol (ET) micellar solutions, with the weight percent of ET changing within the range 0–30, was studied by means of surface tension and conductivity measurements. Surface tension measurements also provided information about the dependence of the surface excess concentration, the minimum area per surfactant molecule, and the standard Gibbs energy of adsorption on the added weight percent of the organic solvent. Information about the degree of counterion dissociation and phase transition was obtained through conductivity measurements. Cyclic voltammetry (CV) and dynamic light scattering (DLS) was also employed to investigate the mixed micellar behavior of the binary mixtures. It was shown that an excess of cationic surfactant and ET resulted in a phase transition of vesicles and large micelles to mixed micelles. The regular solution theory approximation was used to determine various micellar parameters of ideal systems. The regular solution interaction parameter (β) suggests that the formation of mixed micelles is due to the synergistic interactions in the case of TTAB/SDS systems and becomes affected by the water/ET ratio.

Electrical double layer and adsorption of iodide ions at the Bi | acetonitrile interface

The adsorption of I− ions on the Bi(111) single crystal plane from solutions in acetonitrile has been investigated by impedance measurement method. The ionic charge due to the specific adsorption has been obtained using the mixed electrolyte method applied for both electrode charge and electrode potential as the independent electrical variables. The Gibbs energy of ions adsorption has been calculated using the virial adsorption isotherm. It was found that under comparable conditions the results obtained at constant electrode potential and at constant electrode charge are coincident and the Gibbs energy of I− anion adsorption increases in the sequence of solvents: methanol < ethanol < propylene carbonate < acetonitrile. The electrosorption valency has been calculated and it was found that this parameter increases in the sequence propylene carbonate < ethanol < methanol < acetonitrile.

Temperature effect on the adsorption equilibrium at the silica–polyethylene glycol solution interface

The influence of temperature in the range 15–35°C on polyethylene glycol (PEG) adsorption on the silica (SiO2) surface was examined. For this purpose the following methods were applied: spectrophotometry, viscosimetry and potentiometric titrations. They allow determination of polymer adsorbed amounts, its adsorption layer thickness and surface charge density of the solid with the adsorbed PEG. Moreover, viscosity measurements enabled characteristics of macromolecules conformation in the solution, whereas the adsorption experiments – calculation of the Gibbs energy of polymer adsorption. The obtained results indicate that temperature influences the structure of polymer adsorption layer. The temperature rise causes polymer coils developing which results in: the increase of polymer adsorption, its adsorption Gibbs energy, as well as the increase of linear dimensions of PEG chains in the solution and the formation of thicker adsorption layer of the polymer on the solid surface.

A study of the interaction between a phenothiazine drug promazine hydrochloride with cationic surfactants

A tensiometric study at 303.15K was made to study the binary mixed systems of a phenothiazine drug promazine hydrochloride with six cationic surfactants (decyl-, dodecyl-, tetradecyl-, hexadecyltrimethylammonium bromides, and cetylpyridinium bromide/chloride). Relevant parameters were evaluated by using the Regular Solution Theory and Motomura treatment for binary mixed systems. Clint's model was also used to explain the nonideal behavior of the systems. The synergistic behavior (i.e., non-ideal behavior) for binary mixtures is explained by the deviation of critical micelle concentration (cmc) from ideal critical micelle concentration (cmc*), micellar mole fraction (X1m) from ideal micellar mole fraction (X1ideal), the values of interaction parameter (β) and activity coefficients (fi) (for both mixed micelles and mixed monolayer). The excess free energy (ΔGex) explains the stability of mixed micelles in comparison to micelles of pure drug; the stability decreases with the increase in alkyl chain length of the surfactant. Interfacial parameters, i.e., Gibbs surface excess (Γmax), minimum head group area at air/water interface (Amin), free energy of micellization (ΔGmο), and standard Gibbs energy of adsorption (ΔGadsο) were also evaluated for the systems.

Miscibility of imidazolium and pyridinium ionic liquids including BF4− at the air/water interface

We investigated miscibility of ionic liquids in the adsorbed film by surface tensiometry from the viewpoint of effect of the hydrogen bonding between cation and anion. The ion pair formation accompanied by two hydrogen-bond between cation and anion was indicated in 1-hexyl-3-methylimidazolium tetrafluoroborate (C6MIMBF4) system and also in hexylpyridinium tetrafluoroborate (C6PyBF4) system, the ion pairs of which structure is similar to that of C6MIMBF4 systems was suggested. The phase diagram of adsorption (PDA) of the ionic liquid–ionic liquid mixed system (C6PyBF4–C6MIMBF4) showed an ideal mixing. On the other hand, those of ionic liquid–alcohol mixed systems (C6MIMBF4–1-butanol, C6PyBF4–1-butanol) showed positive deviation in the adsorbed film. Judging from the values of excess Gibbs energy of adsorption of these systems, we concluded that the magnitude of the two hydrogen-bonds of C6PyBF4 and C6MIMBF4 is not significantly different, but the one between C6MIM+ and BF4− is slightly larger than that between C6Py+ and BF4−. The difference should be caused by the magnitude of difference of atomic charge distributions in the molecules owing to nitrogen atom in the ions, especially in the C(2)–H.

Physicochemical Studies on the Micellization of Cationic, Anionic, and Nonionic Surfactants in Water–Polar Organic Solvent Mixtures

The effect of cosolvent (ethane-1,2-diol and dimethyl sulfoxide) on the self-assembly of three surfactants, N,N,N-trimethyl-1-dodecanaminium bromide (DTAB), sodium [dodecanoyl(methyl)amino]acetate (SDDS), and polyoxyethylene (20) sorbitan monolaurate (Tween-20) in aqueous solution have been investigated by conductometric, tensiometric, and viscometric techniques at 298 K. The main focus was on the effect of solvent on critical micelle concentration (cmc), free energy contribution to micellization (ΔGm0), tail transfer Gibbs free energy (ΔGtrans0), Gibbs adsorption energy (ΔGads0), and some micellar interfacial parameters, for example, Gibbs surface excess (Γmax), minimum area per surfactant molecule (Amin), surface pressure (Πcmc), and pC20(= −log(C20), where C20 is the surfactant molar concentration required to reduce the surface tension of mixed solvent by 20 mN m–1). With increasing concentration of cosolvent in the binary mixture, the cohesive force decreases, and surfactant molecules are more soluble...

Synthesis and Investigation of Surface Active Properties of Counterion Coupled Gemini Surfactants

AbstractThree counterion coupled gemini (cocogem) surfactants in the series 1,6‐bis(N,N‐alkyldimethylammonium) adipate, referred as n‐6‐n (n = 12, 14, 16), were synthesized, purified and characterized by 1H NMR and 13C NMR. Their physicochemical properties were investigated by electrical conductivity and surface tension measurements. The degree of ionization, critical micelle concentration (CMC), surface excess at the air/solution interface (Γmax), minimum area per surfactant molecule at the air/solution interface (Amin), surface tension at the CMC (γCMC), and pC20 (negative log of the surfactant molar concentration, required to reduce the surface tension of water by 20 mN m−1) were calculated. Increase in tail length of the surfactants increases the efficiency of surfactants to decrease the surface tension of water. Thermodynamic parameters, viz. molar free energy at the maximum adsorption attained at CMC (Gmin), standard Gibb's energy of micellization (), and standard Gibbs energy of adsorption (), were also calculated. The and values show that the monomers were preferred to be adsorbed at the air/water interface and then in the micellar formation in the bulk. Additionally, fluorescence measurements were used to find the aggregation number. Other relevant surface properties (Krafft point, emulsion stability, foaming ability, micellar stability and dye solubilization ability) were also evaluated. These results suggest that with respect to emulsion formation, micellar stability and dye solubilization, the cocogem with a 16‐carbon chain gives better results, producing 89 % more stable foams and shows better aggregational behavior.

Sorption of certain isatins on various sorbents under RP-HPLC conditions

The results from chromatographic analysis of biologically active isatin derivatives on hyper-crosslinked polystyrene (HCLPS) and silica gel modified by octadecyl groups (SilC18) are presented. The constants of distribution of sorbates between a mobile phase and the investigated sorbents (Kx) and the changes in the standard differential molar Gibbs energies of adsorption \((\Delta _a \bar G^\circ )\) are calculated, along with the chromatographic retention-physicochemical property of sorbate dependences. It is found that the equations describing these dependences have high forecasting ability with respect to the values of retention factors of the investigated sorbates.

Ion Distributions at the Water/1,2-Dichloroethane Interface: Potential of Mean Force Approach to Analyzing X-ray Reflectivity and Interfacial Tension Measurements

We present X-ray reflectivity and interfacial tension measurements of the electrified liquid/liquid interface between two immiscible electrolyte solutions for the purpose of understanding the dependence of interfacial ion distributions on the applied electric potential difference across the interface. The aqueous phase contains alkali-metal chlorides, including LiCl, NaCl, RbCl, or CsCl, and the organic phase is a 1,2-dichloroethane solution of bis(triphenylphosphor anylidene) ammonium tetrakis(pentafluorophenyl)borate (BTPPATPFB). Selected data for a subset of electric potential differences are analyzed to determine the potentials of mean force for Li(+), Rb(+), Cs(+), BTPPA(+), and TPFB(-). These potentials of mean force are then used to analyze both X-ray reflectivity and interfacial tension data measured over a wide range of electric potential differences. Comparison of X-ray reflectivity data for strongly hydrated alkali-metal ions (Li(+) and Na(+)), for which ion pairing to TPFB(-) ions across the interface is not expected, to data for weakly hydrated alkali-metal ions (Rb(+) and Cs(+)) indicates that the Gibbs energy of adsorption due to ion pairing at the interface must be small (<1 k(B)T per ion pair) for both the CsCl and RbCl samples. This paper demonstrates the applicability of the Poisson-Boltzmann potential of mean force approach to the analysis of X-ray reflectivity measurements that probe the nanoscale ion distribution and the consequences of these underlying distributions for thermodynamic studies, such as interfacial tension measurements, that yield quantities related to the integrated ion distribution.

Effect and mixing of counter anions at the surface of aqueous solution of imidazolium-based ionic liquids

The purpose of this study was to find the primary factor determining the mixing of the counter anions of 1-alkyl-3-methylimidazolium-based ionic liquid (IL, CnmimX) at the air/water interface. First, the properties of the adsorbed films of the C10mimBr–C10mimBF4 mixtures were estimated by using the thermodynamic analysis of their surface tension data. The mole fraction of BF4− was lower in the adsorbed films than in the ideal state and the excess Gibbs energy of adsorption was negative, which was in marked contrast to those of the C6mimBr–C6mimBF4 mixtures. Meanwhile, the possibility of forming side-by-side ion pair of BF4− and imidazolium ring at the adsorbed films, as we found in the C6mimBr–C6mimBF4 system, was greatly reduced in the present case. These changes were mainly attributed to the reduction in the hydrogen-bonding interaction between BF4− and C10mim+, as the carbon number in the hydrophobic part of Cnmim+ was increased from 6 to 10. In addition, it was found that the values of excess Gibbs energy of adsorption were less negative in the C10mimBr–C10mimBF4 system than in the dodecyltrimethylammonium (C12TA)Br–C12TABF4 system, where the long-range Columbic interaction solely exists between the counter anions and surfactant cations. Thus, we concluded that the short-range hydrogen-bonding interaction played an essential role in the interfacial activity of ILs.

Interaction between Zwitterionic Surfactants and Amphiphilic Drug: A Tensiometric Study

Abstract The physicochemical properties, viz, critical micelle concentration (cmc), surface excess concentration (Γ max), minimum area per head group (A min) of zwitterionic surfactants (designated as n(−)-2-m(+); n = 8, 10, 12 and m = 12, 14, 16) and their mixtures with amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) were determined by using surface tension measurements. The cmc and ideal cmc (cmcid) values along with interaction parameters, β m and β σ (calculated using Rubingh's and Rosen's models), suggest attractive interactions among the components. The Krafft temperature measurements also indicate strong attractive interactions. Γ max (or A min) increases (or decreases) with the addition of gemini surfactant; the values being closer to that of the drug. These values and micellar mole fraction (X1 m-calculated from Rubingh's model and X 1 Moto-calculated from Motomura's model) indicate larger contribution of gemini surfactants in mixed micelles and smaller contribution at air/solution interface (as mole fraction values at interface, X 1 σ , are slightly smaller than X 1 m). The standard Gibbs energy of micellization (Δ G micº) and adsorption (Δ G adº) as well as excess energy of mixing (Δ G ex m) are all negative. All these results suggest higher stability of the mixed systems. UV absorbance results also suggest that the mixed micelles are stable for several days.

Microcalorimetric study of the adsorption of native and mono-PEGylated bovine serum albumin on anion-exchangers

The adsorption of native bovine serum albumin (BSA) and 12kDa-PEG-BSA on 12 different commercially available strong and weak anion-exchange resins is studied at 25°C and pH 7. The resins differ in their base matrix material, their functional groups and the type of polymer modification. A combination of equilibrium measurements and microcalorimetric experiments is used to determine the specific enthalpy of adsorption of the proteins. From these data, the entropic contributions to the specific Gibbs energy of adsorption are determined. The results strongly differ for different resins. They also depend on the loadings. The adsorption of BSA on strong (Q) anion-exchangers is exothermic and enthalpy-driven. The adsorption of BSA on weak (DEAE) anion-exchangers is endothermic and entropy-driven. The adsorption of PEG-BSA on strong (Q) anion-exchangers is exothermic or endothermic, depending on the resin, while the adsorption of PEG-BSA on weak (DEAE) anion-exchangers is exothermic for all studied resins. The present study provides a large body of new experimental data that contribute to the understanding of the nature of protein adsorption on ion exchange resins and the influence of the resin properties and polymer modification of the proteins on this process.