Total carbon analysis for surfactant adsorption

Total carbon analysis can be utilized for the determination of aqueous surfactant solutions at ppm levels. This method was used to generate adsorption isotherms for purified alcohol ethoxylates on polyester fiber where the effect of the degree of ethoxylation was examined. The generality of the method was shown with cationic surfactant adsorption an inorganic substrates.     

Inhibition of nitrobenzene adsorption by water cluster formation at acidic oxygen functional groups on activated carbon

The inhibition effect of nitrobenzene adsorption by water clusters formed at the acidic groups on activated carbon was examined in aqueous and n-hexane solution. The activated carbon was oxidized with nitric acid to introduce CO complexes and then outgassed in helium flow at 1273 K to remove them completely without changing the structural properties of the carbon as a reference adsorbent. The amounts of acidic functional groups were determined by applying Boehm titration. A relative humidity of 95% was used to adsorb water onto the carbon surface. Strong adsorption of water onto the oxidized carbon can be observed by thermogravimetric analysis. The adsorption kinetic rate was estimated to be controlled by diffusion from the kinetic analysis. Significant decline in both capacity and kinetic rate for nitrobenzene adsorption onto the oxidized carbon was also observed in n-hexane solution by preadsorption of water to the carbon surface, whereas it was not detected for the outgassed carbons. These results might reveal that water molecules forming clusters at the CO complexes inhibited the entrance of nitrobenzene into the interparticles of the carbon.     

Joint adsorption of benzene and water on carbon nanotubes

The joint adsorption of water and benzene on nanosized carbon tubes (NCTs) (with a specific surface area of 413 m²/g) synthesized by carbonizing methylene chloride in cylindrical pores of an Al₂O₃ matrix was studied. ¹H NMR spectroscopy with layer-by-layer freezing of the liquid phase was used to characterize the water bound in pores at various contents of benzene and water. Due to its higher energy of interaction with carbon surfaces, benzene was demonstrated to decrease the energy of interaction of water with the surface of the NCT sample from 43 to 15 J/g. It was suggested that, in the presence of benzene, H-bonded water clusters only weakly bound to the surface are formed in the cylindrical cavities of the NCTs.     

The influence of the water content on the adsorption properties of γ-Al2O3

Summary One of the most important parameters which decide the peaks resolution in HPLC with the nonmodified adsorbents, is the amount of water which is present on the adsorbent surface. This article tries to show that the change in the adsorption properties of -Al₂O₃ is dependent on the amount of adsorbed water. These changes are shown with the help of adsorption isotherms, isosteric heats of adsorption and adsorption energy distributions. The data is analysed on the bases of Jovanovic equations. It was also found that a relationship exists between the Brockman activity scale and the adsorption isotherm of water on -Al₂O₃.     

Influence of external electric field on oxygen and carbon monoxide adsorption

The induction of negative charge in a ZnO film causes oxigen adsorption on an oxidized surface apparently in the form of O ₂ ^– . Electroadsorbed oxygen forms CO adsorption centers. On coadsorption from a 2CO+O₂ mixture, equal quantities of CO and O₂ are adsorbed with the formation of CO ₃ ^– complexes decomposing above 400 °C with CO₂ liberation into the gas phase.

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ZnO , -, O ₂ ^– . CO. 2CO+O₂ CO O₂ CO ₃ ^– , 400 °C CO₂ .

     

The adsorption of water isotopomers on carbon adsorbents

Adsorption isotherms were measured by the gas chromatography method over the temperature range 50–80°C, and isosteric heats of adsorption of water isotopomers were calculated in the region of low coverages on two active carbons (Norit and FAS) with similar volumes of micropores (0.38 and 0.37 cm³/g) but different chemical properties of the surface (the surface of active carbon (AC) Norit is hydrophilic and that of AC FAS, hydrophobic). The isotherms on AC Norit were convex and those on AC FAS concave toward the axis of adsorption. At all equilibrium pressures, the adsorption of H₂O and D₂O on AC Norit was much higher than on AC FAS. The isotherms of adsorption of H₂O and D₂O were quite similar on both adsorbents, but the isotherms and heats of adsorption of D₂O were slightly higher than those of H₂O because of small differences in adsorbate-adsorbent and adsorbate-adsorbate interactions and the structure of adsorbate molecules. Original Russian Text ? S.N. Lanin, N.V. Kovaleva, L.A. Litvincheva, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 2, pp. 351–355.     

The oxygen content in supercooled water

Summary The oxygen content in liquid water has been measured in the temperature range between 0°C and –7°C. The measurements have been carried out with an amperometric needle sensor in glass-capillaries with an inner diameter of 1.7 mm. It has been obtained that the oxygen content in water is rapidly increasing as the temperature is lowered below 0°C. At –5°C the concentration of oxygen in water at constant partial pressure of oxygen is by 13% higher than that at +3°C. The increase of oxygen content seems to be related to the unusual temperature dependence of heat capacity, density and isothermal compressibility of supercooled water.Herrn Professor Ulrich Wannagat in alter Verbundenheit zum 70. Geburtstag gewidmet.     

Nitrogen and oxygen mixture adsorption on carbon nanotube bundles from molecular simulation

The adsorption of a nitrogen and oxygen mixture (air) on two types of single-walled carbon nanotube bundles at both sub- and supercritical temperatures is studied using grand canonical Monte Carlo molecular simulation. On an infinite periodic hexagonal bundle without an external surface, adsorption at a subcritical temperature is of type I. With increasing pressure, nitrogen adsorption first increases and then decreases until saturation; oxygen adsorption continues increasing, displacing nitrogen, until saturation. Both nitrogen and oxygen first form annuli inside the nanotubes, then with increased coverage they occupy the nanotube centers, and at the highest coverage some oxygen also adsorbs in the interstitial channels between the nanotubes. The selectivity of nitrogen over oxygen decreases with increasing pressure and reaches a constant near saturation. Adsorption at a supercritical temperature is also of type I, with both nitrogen and oxygen adsorption increasing with increasing pressure, though the selectivity of nitrogen to oxygen first increases slightly and then decreases with increasing pressure. On a small isolated hexagonal bundle with an external surface, adsorption at a subcritical temperature is of type II. With increasing pressure, nitrogen adsorption first increases, then decreases, and finally increases again due to wetting by liquid air, while oxygen adsorption increases continually. Both nitrogen and oxygen adsorb first at the internal annuli and at the grooves, and with increasing pressure, they then adsorb at the ridges and at the nanotube centers; at higher pressures, only oxygen adsorbs in the interstitial channels, and multilayer adsorption and wetting occur on the external surface as the bulk phase approaches saturation. The selectivity, like that of subcritical temperature adsorption on the infinite periodic bundle, decreases with increasing pressure and reaches a constant upon wetting. Adsorption at a supercritical temperature is of type I, with both nitrogen and oxygen adsorption increasing with increasing pressure. The selectivity of nitrogen to oxygen, like that of supercritical temperature adsorption on the infinite periodic bundle, first increases slightly and then decreases with increasing pressure. These results indicate that the adsorption selectivity strongly depends on temperature but only weakly depends on the type of the bundle and that a nitrogen--oxygen mixture (air) might be separated by competitive adsorption on the carbon nanotube bundles.     

Selective adsorption of proteins on single-wall carbon nanotubes by using a protective surfactant

The dispersion of highly hydrophobic carbon materials such as carbon nanotubes in biological media is a challenging issue. Indeed, the nonspecific adsorption of proteins occurs readily when the nanotubes are introduced in biological media; therefore, a methodology to control adsorption is in high demand. To address this issue, we developed a bifunctional linker derived from pyrene that selectively enables or prevents the adsorption of proteins on single-wall carbon nanotubes (SWNTs). We demonstrated that it is possible to decrease or completely suppress the adsorption of proteins on the nanotube sidewall by using proper functionalization (either covalent or noncovalent). By subsequently activating the functional groups on the nanotube derivatives, protein adsorption can be recovered and, therefore, controlled. Our approach is simple, straightforward, and potentially suitable for other biomolecules that contain thio or amino groups available for coupling.     

基于静电喷射法活性多孔磁性炭球的制备及其对亚甲基蓝的吸附

在利用静电喷射一步法获得壳聚糖(CS)磁性微球(Fe₃O4/CS)的基础上,对Fe₃O4/CS进行高温炭化和碱活化处理获得活性磁性多孔炭球(A-Fe₃O4/C),并对A-Fe₃O4/C吸附水中亚甲基蓝(MB)分子的性能进行了研究。在利用扫描电子显微镜、红外吸收光谱仪、比表面分析仪对制备微球的形貌和结构进行分析的基础上,深入研究溶液pH、吸附时间、温度以及活化剂种类等因素对A-Fe₃O4/C吸附性能的影响。研究结果表明,A-Fe₃O4/C对MB的吸附量随着pH值的增加而增大,且经KOH活化后的A-Fe₃O4/C对MB表现出较优的吸附性能。A-Fe₃O4/C对MB的吸附过程符合伪二级动力学方程和Langmuir等温线模型,理论最大吸附容量可达300.6 mg·g^-1。此外,A-Fe₃O4/C表现出良好的重复利用性能,6次循环后对MB的去除率没有明显下降。     

基于静电喷射法活性多孔磁性炭球的制备及其对亚甲基蓝的吸附

在利用静电喷射一步法获得壳聚糖(CS)磁性微球(Fe₃O₄/CS)的基础上,对Fe₃O₄/CS进行高温炭化和碱活化处理获得活性磁性多孔炭球(A-Fe₃O₄/C),并对A-Fe₃O₄/C吸附水中亚甲基蓝(MB)分子的性能进行了研究。在利用扫描电子显微镜、红外吸收光谱仪、比表面分析仪对制备微球的形貌和结构进行分析的基础上,深入研究溶液pH、吸附时间、温度以及活化剂种类等因素对A-Fe₃O₄/C吸附性能的影响。研究结果表明,A-Fe₃O₄/C对MB的吸附量随着pH值的增加而增大,且经KOH活化后的A-Fe₃O₄/C对MB表现出较优的吸附性能。A-Fe₃O₄/C对MB的吸附过程符合伪二级动力学方程和Langmuir等温线模型,理论最大吸附容量可达300.6 mg·g^-1。此外,A-Fe₃O₄/C表现出良好的重复利用性能,6次循环后对MB的去除率没有明显下降。     

Modeling water adsorption in carbon micropores: study of water in carbon molecular sieves

Measurements of water adsorption equilibrium in a carbon molecular sieve are undertaken in order to gain insight into the nature of water adsorption in carbon micropores. The measurements are taken at low concentrations to emphasize the role of oxygen-containing functional groups in the adsorption of water. Comparisons are made with previously published water adsorption data at higher concentrations to provide a data set spanning a wide range of loading. The assembled data set provides an opportunity for comparison of various theories for prediction of water adsorption in carbon micropores. Shortcomings of current theories are outlined, and an analytical theory that is free of these deficiencies is proposed in this investigation. With the consideration of micropore volume and pore size distribution, the experimental data and proposed isotherm model are consistent with previous studies of Takeda carbon molecular sieves. Also investigated is the uptake kinetics of water, which is characterized by a Fickian diffusion mechanism. The Maxwell-Stefan formulation is applied to characterize the dependence of the diffusional mobility upon loading.     

Influence of carbon dioxide on the position of oxygen adsorption equilibrium on silver

Due to interaction with carbon dioxide, when some adsorbed oxygen atoms on silver surfaces are converted into carbonate groups, the binding energy diminishes and the volatility of adsorbed oxygen rises.

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, , .

     

Simulated water adsorption in chemically heterogeneous carbon nanotubes

Grand canonical Monte Carlo simulations are used to study the adsorption of water in single-walled (10:10), (12:12), and (20:20) carbon nanotubes at 298 K. Water is represented by the extended simple point charge model and the carbon atoms as Lennard-Jones spheres. The nanotubes are decorated with different amounts of oxygenated sites, represented as carbonyl groups. In the absence of carbonyl groups the simulated isotherms are characterized by negligible amounts of water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption-desorption hysteresis loops. In the presence of a few carbonyl groups the simulated adsorption isotherms are characterized by pore filling at lower pressures and by narrower adsorption-desorption hysteresis loops compared to the results obtained in the absence of carbonyl groups. Our results show that the distribution of the carbonyl groups has a strong effect on the adsorption isotherms. For carbonyl groups localized in a narrow section the adsorption of water may be gradual because a cluster of adsorbed water forms at low pressures and grows as the pressure increases. For carbonyl groups distributed along the nanotube the adsorption isotherm is of type V.     

1H NMR relaxation of water: a probe for surfactant adsorption on kaolin

In this study, (1)H NMR is used to investigate properties of sodium dodecyl sulfate (SDS), tetradecyl trimethyl ammonium bromide (TTAB), and dodecyl trimethyl ammonium bromide (DTAB) adsorbed on kaolin by NMR T(1) and T(2) measurements of the water proton resonance. The results show that adsorbed surfactants form a barrier between sample water and the paramagnetic species present on the clay surface, thus significantly increasing the proton T(1) values of water. This effect is attributed to the amount of adsorbed surfactants and the arrangement of the surfactant aggregates. The total surface area covered by the cationic (DTAB and TTAB) and anionic (SDS) surfactants could be estimated from the water T(1) data and found to correspond to the fractions of negatively and positively charged surface area, respectively. For selected samples, the amount of paramagnetic species on the clay surface was reduced by treatment with hydrofluoric (HF) acid. For these samples, T(1) and T(2) measurements were taken in the temperature range 278-338 K, revealing detailed information on molecular mobility and nuclear exchange for the sample water that is related to surfactant behavior both on the surface and in the aqueous phase.     

Surface methylation of aerosil and its influence on the adsorption of water

Reversible adsorption isotherms at different temperatures have been used to study the system of water adsorbed on Aerosil and on Aerosil whose surface has been partially methylated with trimethylchlorosilane.The change in the shape of the isotherm upon surface methylation from type II to type III, according to Brunauer's classification, renders difficult the calculation of the capacity of the monolayer; however, in this case it can be obtained by Kaganer's method.The variation in the mobility of the monolayer on surface methylation can be shown by comparing the experimental and theoretical integral entropies, while the molecules adsorbed in the multilayer region always have a high degree of freedom.     

Regular microstructures in gel–surfactant complexes: Influence of water content and comparison with the surfactant structure in water

Interaction of slightly crosslinked hydrogels of poly(diallyldimethylammonium chloride) (PDADMACI) and of copolymer DADMACI/acrylamide (AAm) with sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfate (SDBS) results in significant shrinking of the gels due to the formation of polymer-surfactant complexes. Jump-wise transitions in the collapsed state were observed for the networks with the content of cationic groups 100 and 75 mol %. The structure of complexes was studied by means of X-ray scattering method. The scattering curves for collapsed gels, where most chloride anions were replaced by anions of SDS, show a set of well-pronounced narrow diffraction maxima. Fully charged “wet” complexes studied at the equilibrium swelling conditions exhibit high degree of ordering, which diminishes upon drying with the simultaneous transition from hexagonal to lamellar type of ordering. In contrast to this, for DADMACl/AAm copolymer gels (75 mol % of DADMACl monomers in the initial polymerization mixture) the ordering is less pronounced in the “wet” state and becomes more perfect upon drying. The SDS aqueous solutions of the same concentration in the absence of gel do not show such high degree of ordering, while the system of SDS/neutral AAm gel exhibits lamellar ordering typical for low-temperature phases of SDS solutions. © 1996 John Wiley & Sons, Inc.     

Effects of ionic surfactant adsorption on single-walled carbon nanotube thin film devices in aqueous solutions

Field-effect transistors were fabricated using high-density single-walled carbon nanotube (SWNT) thin films directly grown on suitable substrates. Such approach eliminated the variations of device behaviors in individual SWNT devices by utilizing a large number of SWNTs in each device. We have found that the behaviors of such devices are closely related to the surface charge densities around SWNTs in aqueous solutions. Adsorption of ionic surfactants on the surface could significantly modulate the device characteristics, which could be detected by measuring the conductance of the devices. The devices could be tuned to be sensitive to either anionic or cationic surfactants by tailoring the surface properties of SiO(2) substrates around SWNTs. This effect could be potentially used to design chemical and biological sensors.     

Anionic surfactant adsorption on to asphalt-covered clays

Asphalt adsorption from from water-saturated tolene on Na⁻ kaolinite, Ca²⁻ kaolinite, Na⁻ illite and Ca²⁻ illite clays was investigated. It was found that the kaolinite surface adsorbed more asphalt than illite for both the Na⁻ -and the Ca²⁻ exchanged forms. Adsorption from aqueous solutions of sodium dodecylbenzenesulphonate (SDBS) and sodium dodecyl sulphate (SDS) on various asphalt-covered clays was also studied. The shape of the isotherms depended on the asphalt-clay substrate and showed a much lower adsorption of SDBS beyond the CMC. Desorption of asphalt from various clays with SDBS and SDS surfactants was measured spectrophotometrically. The percentage weight of asphalt desorbed with SDBS was twofold higher than that desorbed with SDS surfactant.