烷基硫酸钠在二氧化钛上的吸附研究

表面活性剂在氧化物表面上的吸附,因其在浮选中的重要作用而被广泛研究。但迄今为上的工作多是关于表面活性离子在电性相反的氧化物表面上,例如阳离子表面活性剂在带负电的氧化物表面上的吸附,而对电性相同的表面活性离子的吸附则很少涉及,虽然许多实际问题中遇到的是后一种情形。本工作研究了烷基硫酸钠在带负电的TiO₂表面上的吸附,根据吸附与电泳的实验结果计算了吸附自由能,并提出了可能的吸附机理。     

Hofmeister effect on the interfacial dynamics of single polymer molecules

The Hofmeister effect on interfacial dynamics has been discovered for single charged polymer molecules (sodium polystyrene sulfonate) adsorbed on a hydrophobic surface from an aqueous solution. The presence of ions in the aqueous solution affects the surface diffusivity, and its amplitudes and the surface friction follow the Hofmeister series-the kosmotropic ions slowed down the surface diffusivity and the chaotropic ions speeded it up. The amplitude of the surface friction exhibits a good correlation with the surface tension increment, indicating the interfacial feature of the Hofmeister effect.     

Adsorption of fluoride ions onto carbonaceous materials

The characteristics of fluoride ion adsorption onto carbonaceous materials were derived as adsorption isotherms at different temperatures and in different pH solutions. The fluoride ion was adsorbed into pores in carbonaceous materials produced from wood; the larger the specific surface area, the more fluoride ions adsorbed. Bone char was the most effective adsorbent. The composition of bone char includes calcium phosphate, calcium carbonate, and so on. This suggests that the phosphate ion in bone char was exchanged with a fluoride ion. Moreover, the mechanism of fluoride ion adsorption onto bone char is clearly chemical in nature because the amount of fluoride ion adsorbed onto bone char increased with increasing temperature and decreasing pH. The amount of fluoride ion adsorbed onto bone char was also shown to depend on the concentration of sodium chloride in solution because of the "salting-out" effect. The adsorption of fluoride ion onto bone char is endothermic. Bone char can be utilized to remove fluoride ions from drinking water.     

Adsorption of monovalent and divalent cations on planar water-silica interfaces studied by optical reflectivity and Monte Carlo simulations

Adsorption on planar silica substrates of various monovalent and divalent cations from aqueous solution is studied by optical reflectivity. The adsorbed amount is extracted by means of a thin slab model. The experimental data are compared with grand canonical Monte Carlo titration simulations at the primitive model level. The surface excess of charge due to adsorbed cations is found to increase with pH and salt concentration as a result of the progressive dissociation of silanol groups. The simulations predict, in agreement with experiments, that the surface excess of charge from divalent ions is much larger than from monovalent ions. Ion-ion correlations explain quantitatively the enhancement of surface ionization by multivalent cations. On the other hand, the combination of experimental and simulation results strongly suggests the existence of a second ionizable site in the acidic region. Variation of the distance of closest approach between the ions and surface sites captures ion specificity of water-silica interfaces in an approximate fashion.     

Adsorption of sodium dodecylsulfate on chrysotile

Adsorption of sodium dodecylsulfate (SDS) onto chrysotile from aqueous solutions was investigated along with varying temperature, ionic strength and surface treatments. Commercial chrysotile fibers were treated by sonication or extensive washings. The ratio of adsorbed SDS per gram of chrysotile is approximately constant with varying chrysotile masses. A steady state is reached after about 2 h of contact between SDS and chrysotile. In general, less surfactant is adsorbed on the sonicated chrysotile than on the extensively washed chrysotile. For the sonicated chrysotile, isotherms presented an adsorption maximum in the region of the surfactant critical micelle concentration, when the experiments were carried out without ionic strength control. The adsorption maximum is due to the presence of magnesium ions in the solution, which can form complexes with dodecylsulfate ions. For the extensively washed chrysotile, the isotherm behavior is similar to that obtained with sonicated chrysotile in the presence of an inert electrolyte. No significant difference in adsorption of SDS on the extensively washed chrysotile was observed when varying temperature or ionic strength. The adsorption of SDS was found to be dependent on the prior surface treatment.     

Water density in the electric double layer at the insulator/electrolyte solution interface

I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of "image forces" between the cationic Na(+) and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field approximately 10(9)-10(10) V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.     

The thermodynamic characteristics of adsorption of hydrogen,sodium, and potassium chlorides at the aqueous solution-gas interface

Thermodynamic models of the adsorption of ions at the interphase boundary between a solution of a 1,1-electrolyte and a gas are suggested. The experimental surface tension isotherms and the isotherms of excess adsorption of hydrogen, sodium, and potassium chlorides from aqueous solutions were used to show that the formation of the surface layer followed both the mechanism of coadsorption of the anion and cation and the mechanism of predominant adsorption of one of the ions. The calculated total adsorption isotherms were used to obtain the dependences of the heats and entropies of adsorption on the amount of the ion adsorbed. The results are discussed in terms of the solvation and desolvation of electrolyte ions in bulk solution and at liquid-vapor interfaces.     

十二烷基苯磺酸钠在SiO2表面聚集的分子动力学模拟

采用分子动力学方法研究了阴离子表面活性剂十二烷基苯磺酸钠(SDBS)在无定形SiO2固体表面的吸附. 设置不同的水层厚度, 观察固液界面和气液界面吸附的差异. 模拟发现表面活性剂分子能够在短时间内吸附到SiO2表面, 受碳链和固体表面之间相互作用的影响形成表面活性剂分子层, 并依据吸附量的大小形成不同的聚集结构; 在水层足够厚的情况下, 由于有较多的表面活性剂分子吸附在固体表面,从而形成带有疏水核心的半胶束结构; 计算得到的成对势表明极性头与钠离子或水分子之间的结合或解离与二者之间的能垒有关, 解离能垒远大于结合能垒, 引起更多Na+聚集在极性头周围而只有少数Na+存在于溶液中; 无论气液还是固液界面, 极性头均伸向水相, 与水分子形成不同类型的氢键. 模拟表明, 分子动力学方法可以作为实验的一种补充, 为实验提供必要的微观结构信息.     

Effect of equimolar salt to decyltrimethylammonium decyl sulfate on vesicle formation and surface adsorption

The aqueous solution of mixture of sodium decyl sulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) has been found to form equilibrium multilamellar vesicles (MLV) spontaneously. We measured the surface tension of the aqueous solution of 1:1 mixture of SDeS and DeTAB as a function of temperature T at various molalities m under atmospheric pressure. The surface density, the entropy of adsorption and the entropy of vesicle formation are evaluated and compared with those of the decyltrimethylammonium decyl sulfate (DeTADeS) aqueous solution system to investigate the role of small counterions in the mechanism of equilibrium vesicle formation. The saturated surface density Gamma (H,C ) vs T curve of the SDeS/DeTAB system sits below that of the DeTADeS system. Therefore, sodium and bromide ions are negatively adsorbed and nevertheless, they neutralize the electric charge of the decyl sulfate ion DeS(-) and the decyltrimethylammonium ion DeTA(+) to some extent to weaken the electrostatic attraction between the polar head groups in the adsorbed film. The net surfactant concentration required for vesicle formation was larger in the SDeS/DeTAB system. Hence, the electrostatic attraction between the polar head groups of the surfactant ions which is one of the major driving forces for vesicle formation is weakened by the presence of the counterions Na(+) and Br(-). Small but distinct changes in the surface density and the entropies of MLV formation of the SDeS/DeTAB system from those of the DeTADeS system were also found.     

The influence of complexing agents on the effectiveness of electrochemical masking with anionic surfactants in anodic stripping voltammetry

The influence of sodium dodecyl sulphate, sodium dodecyl sulphonate and sodium stearinate on the anodic stripping peaks of Tl(I), Pb(II), Cd(II), Cu(II) and In(III) was investigated. The supporting electrolytes were 0.5M sodium sulphate solution, 0.2M citrate solution (pH 3.7, 4.6 and 7.3), 0.5M tartrate solution (pH 4.4) and 0.1M solution of EDTA (pH 4.4). The composition of complex compounds forming in a solution under experimental conditions was defined. The conditions of ion reduction of metals on hanging mercury electrode during the electrolytical deposition were investigated. The investigation included an analysis of voltammetric curves of the metal ions. The obtained results suggest that "electrochemical masking" is much stronger in electrolytes containing a complexing agent than in the sodium sulphate solution. The influence of the complexing agent may not be explained in terms of the interaction between the form of the complex and the charge of the adsorbed surfactant particles; rather the complexing process is connected with indirect inhibition, i.e., by decreasing the rate of charge transfer reaction.     

Aggregation and dispersion of small hydrophobic particles in aqueous electrolyte solutions

The effect of salts on the solvent-induced interactions between hydrophobic particles dispersed in explicit aqueous solution is investigated as a function of the salt's ionic charge density by molecular dynamics simulations. We demonstrate that aggregates of the hydrophobic particles can be formed or dissolved in response to changes in the charge density of the ions. Ions with high charge density increase the propensity of the hydrophobic particles to aggregate. This corresponds to stronger hydrophobic interactions and a decrease in the solubility (salting-out) of the hydrophobic particles. Ions with low charge density can either increase or decrease the propensity for aggregation depending on whether the concentration of the salt is low or high, respectively. At low concentrations of low charge density ions, the aggregate forms a "micelle-like" structure in which the ions are preferentially adsorbed at the surface of the aggregate. These "micelle-like" structures can be soluble in water so that the electrolyte can both increase the solubility and increase aggregation at the same time. We also find, that at the concentration of the hydrophobic particles studied (approximately 0.75 m), the aggregation process resembles a first-order transition in finite systems.     

Structure of electrolyte solutions sorbed in carbon nanospaces, studied by the replica RISM theory

The replica RISM theory is used to investigate the structure of electrolyte solutions confined in carbonized polyvinylidene chloride (PVDC) nanoporous material, compared to bulk electrolyte solution. Comparisons are made between the models of electrolyte solution sorbed in the carbonized PVDC material and a single carbon nanosphere in bulk electrolyte solution. Particular attention is paid to the chemical potential balance between the species of the sorbed electrolyte solution and the bulk solution in contact with the nanoporous material. As a result of the strong hydrophobicity of the carbonized PVDC material in the absence of activating chemical groups, the densities of water and ions sorbed in the material are remarkably low compared to those in the ambient bulk solution. The interaction between water molecules and cations becomes strong in nanospaces. It turns out that, in carbon nanopores, a cation adsorbed at the carbon surface is fully surrounded by the hydration shell of water molecules which separates the cation and the surface. Distinctively, an anion is adsorbed in direct contact with the carbon surface, which squeezes a part of its hydration shell out. The tendency increases toward smaller cations, which are characterized as "positive hydration" ions. In the bulk, cations are not hydrated so strongly and behave similarly to anions. The results suggest that the specific capacitance of an electric double-layer supercapacitor with nanoporous electrodes is intimately related to the solvation structure of electrolyte solution sorbed in nanopores, which is affected by the microscopic structure of the nanoporous electrode.     

Characterization of the adsorption state of carbonate ions at the Au(111) electrode surface using in situ IRAS

The spectro-electrochemical behavior of carbonate and bicarbonate ions at the Au(111) electrode surface was studied using the infrared reflection absorption spectroscopy (IRAS). An absorption band caused by the adsorbed carbonate ions was observed in the wavenumber region of 1425–1511 cm⁻¹ both in Na₂CO₃ and NaHCO₃ solutions. It was concluded that the adsorbed carbonate ions co-ordinate with the electrode surface in the unidentate state with their symmetry axis normal to the substrate. This orientation is retained in the whole potential region where carbonate ions adsorb on the electrode surface in contrast to the behavior of the carbonate ions adsorbed on the Pt(111) electrode surface.     

Adsorption at the air/water interface in dodecylammonium chloride/sodium dodecyl sulfate mixtures

The composition and properties of the adsorption films of dodecylammonium chloride/sodium dodecyl sulfate at the air/water interface depend on interactions between the film molecules and equilibria in the bulk phase (monomer-micelle and/or monomerprecipitate equilibria).The negative value of surface molecular interaction parameter ^mon calculated using the regular solution theory indicates strong attractive interactions between adsorbed molecules. Electrostatic interactions between oppositely charged ionic head groups enhance the adsorption of surfactants and decrease the minimum molar area of surfactant molecules at the air/water interface. The addition of an oppositely charged surfactant enhances packing at the air/water interface and transition from a liquid expanded to a liquid condensed state. Surface potential measurements reveal positive values for the mixtures investigated, implying the cationic surfactant ions are closer to the surface than the anionic ones.     

Adsorption behavior of partially collapsed polyacrylate coils on mica surfaces: A reciprocal space approach

In this article, we investigate tapping mode atomic force microscopy images of intermediate states along the coil to globule transition of sodium polyacrylate coils containing Ca²⁺ as specifically binding ions. The structural correlations within single adsorbed molecules are established using power spectral density (PSD) curves. The PSD curves of several single molecules are averaged to give the so called 2D form factor so as to obtain information of higher statistical merit. A proper interpretation of the 2D form factor and comparison with form factor analysis of the very same sample solution available through small angle neutron scattering provides an alternative quantification of changes in conformation which a single polyacrylate molecule undergoes as it moves from 3D solution to 2D surface and is inevitably distorted in shape because of sample history. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1553–1561, 2010     

An in situ FTIR-ATR study of polyacrylate adsorbed onto hematite at high pH and high ionic strength

FTIR-ATR was used to examine in situ the interaction of polyacrylate and hematite at pH 13. Static light scattering and mobility measurements were used to assess solution polyacrylate dimensions and hematite surface charge, respectively. Polyacrylate adsorption occurred only with the addition of electrolyte (e.g., NaCl), and it was found that excess cations, up to approximately 1 M, facilitated adsorption, above which the effect was found to plateau. At pH 13 and at low ionic strength, adsorption of polyacrylate onto hematite is facilitated by cations in solution shielding both the negative acrylate functionality of the polymer and the negative hematite surface. The shielding of the hematite surface continues to increase with increasing salt concentration up to a measured 3 M. Similarly, the shielding of the polymer increased with electrolyte concentration up to approximately 1 M salt, beyond which no further increase in shielding was observed. At this concentration the polymer assumes a finite minimum size in solution that ultimately limits the amount adsorbed. The dimension of the polymer in solution was found to be independent of monovalent cation type. Thus, at high pH and high ionic strength adsorption is determined by the degree of hematite surface charge reduction. The cation-hematite surface interaction was found to be specific, with lithium leading to greater polyacrylate adsorption than sodium, which was followed by cesium. The stronger affinity of lithium for the hematite surface over sodium and cesium is indicative of the inverse lyotropic adsorption series and has been rationalized in the past by the "structure-making-structure-breaking" model. These results provide a useful insight into the likely adsorption mechanism for polyacrylate flocculants at high pH and ionic strength onto residues in the Bayer processing of bauxite.     

Über die Chemie der Oberfläche des Titandioxids. III. Reaktionen der basischen Hydroxylgruppen auf der Oberfläche

Adsorption of various acids on anatase of high surface area was studied. Phosphoric, arsenic, sulphuric and acetic acid are specifically adsorbed; hydrochloric and perchloric acid are not adsorbed. Phosphate ions are bound on the TiO₂ surface also from NaH₂PO₄ and Na₂HPO₄ solutions; sodium ions are adsorbed at the same time. OH^? ions on the surface are replaced by anions such as H₂PO in these reactions. The bonding of adsorbed phosphate ions is not purely ionic. Infrared spectra show that adsorbed acetic acid is bound as acetate. NO₂ reacts with the basic OH^? ions undergoing disproportionation; OH^? ions are replaced by NO ions. Phophoric acid adsorption corresponded always to half the total OH population on five different TiO₂ samples. The TiO₂ surface is not completely covered by OH groups. The maximum coverage is ca. 7.5 μMol OH/m².     

Effect of the Head Group of Surfactant on the Miscibility of Sodium Chloride and Surfactant in an Adsorbed Film and Micelle

The thermodynamic treatment of a surfactant mixture was applied to the mixture of sodium chloride, NaCl, with octyl methyl sulfoxide (OMS) and that with decyldimethylphosphine oxide (DePO). The surface tension of aqueous solutions of the mixtures was measured as a function of the total concentration and the composition of the mixtures at 298.15 K. The total surface densities of the mixtures and the composition of the adsorbed films and micelles were evaluated by applying thermodynamic equations to the expeimental results. It was found that the adsorbed film and micelle are almost composed of the surfactant and there is slight attractive interaction between the ions of NaCl and the head groups of OMS and DePO molecules in the adsorbed films and micelles. A difference in the miscibility of NaCl and surfactant was observed between the OMS and DePO systems and attributed to the difference in the hydration of the head group between OMS and DePO molecules. The comparison of these results with those of the mixtures of NaCl with tetraethylene glycol monooctyl ether (C(8)E(4)) and dodecylammonium chloride (DAC) indicated that the small difference in the miscibility in an adsorbed film and micelle among these nonionic surfactant systems arises from the difference in hydration and structure of the head groups and the large one between the nonionic surfactant and DAC systems results from electrostatic interactions between dodecylammonium and sodium ions. Copyright 2001 Academic Press.     

Mapping CTTS dynamics of Na- in tetrahydrofurane with ultrafast multichannel pump-probe spectroscopy

Using multichannel femtosecond spectroscopy we have followed Na- charge transfer to solvent (CTTS) dynamics in THF solution. Absorption of the primary photoproducts in the visible, resolved here for the first time, consists of an asymmetric triplet centered at 595 nm, which we assign to a metastable incompletely solvated neutral atomic sodium species. Decay of this feature within approximately 1 ps to a broad and structureless solvated neutral is accompanied by broadening and loss of spectral detail. Kinetic analysis shows that both the spectral structure and the decay of this band are independent of the excitation photon frequency in the range 400-800 nm. With different pump-probe polarizations the anisotropy in transient transmission has been charted and its variation with excitation wavelength surveyed. The anisotropies are assigned to the reactant bleach, indicating that due to solvent-induced symmetry breaking, the CTTS absorption band of Na- is made up of discreet orthogonally polarized sub bands. None of the anisotropy in transient absorption could be associated with the photoproduct triplet band even at the earliest measurable time delays. Along with the documented differences in the spatial distribution of ejected electrons across the tested excitation wavelength range, these results lead us to conclude that photoejection is extremely rapid, and that loss of correlations between the departing electron and its neutral core is faster than our time resolution of approximately 60 fs.     

Viscometric study of the coil-globule transition of poly(N-isopropylacrylamide) in solutions of surfactant

The coil-globule transition of poly(N-isopropylacrylamide) (systematic name: poly-[1-(isopropylaminocarbonyl)ethylene]) has been viscometrically investigated in low-concentration aqueous sodium dodecyl sulfate solution. In this environment, even if the macromolecular coils collapse as the temperature increases above the lower critical solution temperature of the polymer, 34°C, the polymer does not precipitate. It seems that the hydrophobically collapsed macromolecular coils do not aggregate, but remain in solution with the aid of surface charges supplied by surfactant ions adsorbed through hydrophobic interactions.