Decrease in the solubility product of hydroxyapatite by the adsorption of surface-active ion

The solubility product (Ksp) of hydroxyapatite (HAP) in ionic surfactant solutions decreased with an increase in the adsorbed amount of the surface-active ions (dodecylammonium and dodecyl sulfate ions). In the presence of nonionic surfactant (polyoxyethylene(10) octylphenyl ether), Ksp was almost constant within the limit of experimental error. It was concluded that the decrease in Ksp is due to the decrease in the chemical potential of HAP through the adsorption of the surface-active ion on HAP, and due to the spontaneous change in the constituent ions of the HAP surface (i.e., surface complex formation) by ion-exchange with the surface-active ion.     

Characterisation of organoclays and adsorption of p-nitrophenol: environmental application

Organoclays were synthesised through ion exchange of a single surfactant for sodium ions, and characterised by a range of method including X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The change in surface properties of montmorillonite and organoclays intercalated with the surfactant, tetradecyltrimethylammonium bromide (TDTMA) were determined using XRD through the change in basal spacing and the expansion occurred by the adsorbed p-nitrophenol. The changes of interlayer spacing were observed in TEM. In addition, the surface measurement such as specific surface area and pore volume was measured and calculated using BET method, this suggested the loaded surfactant is highly important to determine the sorption mechanism onto organoclays. The collected results of XPS provided the chemical composition of montmorillonite and organoclays, and the high-resolution XPS spectra offered the chemical states of prepared organoclays with binding energy. Using TGA and FT-IR, the confirmation of intercalated surfactant was investigated. The collected data from various techniques enable an understanding of the changes in structure and surface properties. This study is of importance to provide mechanisms for the adsorption of organic molecules, especially in contaminated environmental sites and polluted waters.     

Ultra-clean Si(111) and Si(001) Surfaces Prepared by Advanced Wet Chemical Cleaning

Wet chemical cleaning of silicon is a critical step, e.g., pre-gate clean, in the semiconductor manufacturing^[1]. For example, pre-gate oxide cleaning demands ultra-clean silicon surface with least surface roughness. It is well known that metallic infinities and roughness cause the lower breakdown voltage in gate dielectric^[2]. It has stringent requirements for ultra-clean and atomically flat silicon surface as the thickness of gate oxide is decreasing. In the present work, we have extended our study on Si(100) surface13] and extensively investigated wet chemical cleaning of Si(111) and Si(100) surfaces in NH₄F-based solutions by using scanning tunneling microscopy (STM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS) and total reflection X-ray fluorescence spectrometry (TXRF). Surface roughness, organic contamination, metallic impurities and surface termination on the silicon surfaces after wet chemical cleaning with various NH₄F-based solutions have been determined and compared with those treated with RCA cleans, HF solutions and other industrially used solutions. Our results indicate that ultra-clean and smooth Si(111) and Si(001) surfaces are obtained by treatment with NH4F-based solutions.     

Surface modification of natural rubber film by polymerisation of methyl methacrylate in water-based system

Polymerisation of methyl methacrylate (MMA) on the surface of natural rubber (NR) film was studied in order to increase the surface hardness, roughness and, hence, to decrease the friction coefficient of rubber. We used the two-step process: (i) swelling of MMA and tert-butyl hydroperoxide, emulsified in an aqueous solution of sodium dodecyl sulphate, onto the NR film surface, and (ii) subsequently immersing the swollen rubber strip into an alkaline aqueous solution of ferrous ion/fructose for redox initiation. The presence of PMMA on the NR surface was examined by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Increasing the concentration of ferrous ion caused an increase in MMA conversion. The surface morphology observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) in tapping mode revealed the aggregation of micronmetre-scale nodules on the modified surface. The surface hardness and roughness increased with increasing PMMA content.     

Reaction of N,N-Dimethyl-N′-(2-hydroxybenzyl)ethylenediamine with Copper(II) in the Presence of Surfactants

The protolytic properties of N,N-dimethyl-N′-(2-hydroxybenzyl) ethylenediamine (HL) and its complexation with copper(II) in the presence of cationic (cetyltrimethylammonium bromide) and nonionic (Triton X-100) surfactants were studied by pH-metry, spectrophotometry, and mathematical simulation of the equilibria. Cetyltrimethylammonium bromide affects the H₂L₂ ⇄ 2HL equilibrium. Along with the protonated monomeric and dimeric species, triprotonated tetrameric species were revealed in surfactant solutions, as in aqueous solutions of isopropyl alcohol. The surfactants affect the complexation of HL with Cu(II). The 1 : 2 complex with the phenolate form in solutions of cetyltrimethylammonium bromide is formed in a more acidic medium (pH ∼5.5) compared to an aqueous solution of isopropyl alcohol (pH ∼11). The apparent stability constants of the complexes increase in the presence of surfactants, especially of cetyltrimethylammonium bromide.__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 3, 2005, pp. 379–382.Original Russian Text Copyright © 2005 by Sal’nikov, Boos, Ryzhkina, Ganieva.     

Corrosion and passivity of metals in methanol solutions of electrolytes

Electrochemical and corrosion behaviour of metals in alcohols are the subject of numerous investigations because of the application of mentioned solvents in chemical engineering, production of oxide nanoparticles (sol-gel techniques) and application of alcohols as fuels. Despite relatively rich bibliography related to electro-catalytic oxidation of alcohols on metal surface in mixed aqueous–alcohol solutions, the knowledge of the mechanism of reactions on metal/anhydrous alcohol interface is still not sufficient. Anodic oxidation of metal surface in alcohol leads to several electro-catalytic reactions with formation of surface compounds being the product of metal and alcohol oxidation. Identification of these products is very difficult. Therefore, our knowledge of the composition and structure of passive films or corrosion products on metal surface in anhydrous alcohol solvents is poor. Our paper presents the investigations of anodic behaviour of metals (Cu, Zn, Fe, Ni, Al and Ti) and semiconductors (p-Si) in methanol solutions of electrolytes, performed in our laboratory within the last 10 years. On the base of electrochemical measurements (linear sweep voltammetry, electrochemical impedance spectroscopy), spectroscopic investigations (X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy and low-energy electron diffraction) and scanning electron microscopy techniques, the role of metal–alcohol intermediates in the formation of surface and soluble compounds is discussed. The practical application of electrochemical etching of metals as a method of production of micro- and nanoparticles of metals and oxides is also shown.     

Distribution of surfactant ions near the surface of non-aqueous solution gained by angular resolved X-ray photoelectron spectroscopy

Angular resolved X-ray photoelectron spectroscopy (ARXPS) has been applied to obtain the distribution of chemical elements near the surface of non-aqueous solutions containing surfactants. However, such profiles can only yield a quantitative relation between those constituents near the surface regime of sample. With the knowledge of the molar volumes of surfactant and solvent, we have obtained the molar concentration-depth profiles via the molar fraction-depth profiles that were reconstructed by ARXPS with the help of a generic algorithm. The concentration profiles show detailed distributions of the surfactant ions near the surface, which provide a direct insight into the surface picture of the surfactant solution.

Chemical potential of a nonionic surfactant in solution

The chemical potential of a surfactant in solution can be calculated from the Gibbs adsorption equation when the surface excess of the surfactant and the surface tension of the solution as a function of surfactant concentration are known. We have investigated a solution of the nonionic surfactant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the polar solvent 3-hydroxypropionitrile at concentrations below and above the critical micelle concentration (cmc). Neutral impact collision ion scattering spectroscopy was applied for the direct measurement of the surface excess of POPC as a function of concentration. The Gibbs adsorption equation was applied in conjunction with surface tension measurements to evaluate the chemical potential and the activity coefficients of POPC, respectively. We find that the solution shows ideal behavior up to the cmc and that the chemical potential remains constant at concentrations larger than the cmc.     

双功能改性的T型分子筛膜用于有机溶剂脱水

将3-氨丙基三乙氧基硅烷（APTES）引入到T型分子筛膜表面,用以修饰多晶膜合成过程中产生的缺陷。X射线衍射、场发射扫描电子显微镜、X射线光电子能谱和FT-IR等方法的表征结果显示,APTES通过“键合”的形式被成功地修饰到膜表面上。APTES层起到2个作用：一是提高膜的亲水性;二是减少膜层的缺陷。将修饰后的膜应用在348 K、90%的异丙醇水溶液的脱水时,该膜表现出比较高的分离因子和通量。该方法重复性良好,5个修饰后的膜样品的选择性平均增加了大约8倍（从359±23增加到2 934±183）,而渗透通量仅仅从（3.52±0.10） kg·m^-2·h^-1降低到（3.06±0.14） kg·m^-2·h^-1（减少13.07%）。在363 K下,修饰的膜经过100 h的连续测试,膜渗透测得的水含量均可达到99.50%以上,表明修饰后的膜性能较稳定。     

Adlayers of dimannoside thiols on gold: surface chemical analysis

Carbohydrate films on gold based on dimannoside thiols (DMT) were prepared, and a complementary surface chemical analysis was performed in detail by X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), near-edge X-ray absorption fine structure (NEXAFS), FT-IR, and contact angle measurements in order to verify formation of ω-carbohydrate-functionalized alkylthiol films. XPS (C 1s, O 1s, and S 2p) reveals information on carbohydrate specific alkoxy (C-O) and acetal moieties (O-C-O) as well as thiolate species attached to gold. Angle-resolved synchrotron XPS was used for chemical speciation at ultimate surface sensitivity. Angle-resolved XPS analysis suggests the presence of an excess top layer composed of unbound sulfur components combined with alkyl moieties. Further support for DMT attachment on Au is given by ToF-SIMS and FT-IR analysis. Carbon and oxygen K-edge NEXAFS spectra were interpreted by applying the building block model supported by comparison to data of 1-undecanethiol, poly(vinyl alcohol), and polyoxymethylene. No linear dichroism effect was observed in the angle-resolved C K-edge NEXAFS.     

Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz-water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion-surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film-water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.     

电化学还原预处理对BiVO_4薄膜电极光电化学氧化水性能的提高

在酸性水溶液中(pH=2.0),采用电化学还原(ER)方法对BiVO4薄膜电极进行预处理,并探讨了其对薄膜电极光电化学氧化水性能的影响.结果表明,这种预处理可显著提高电极的光电化学氧化水的性能,且具有良好的光电化学稳定性.利用扫描电子显微镜、X射线衍射、拉曼光谱、光电子能谱、紫外-可见漫反射光谱、荧光光谱、电化学阻抗谱及Mott-Schottky等方法对ER处理前后的电极进行了表征.结果表明,ER预处理使电极粗糙度增大,表面积增大约1.4倍;电极材料的晶型无明显变化,但V—O对称伸缩振动略有红移;表面Bi,V和O结合能变小,Bi3+部分被还原,Bi/V原子比增大;ER处理导致电极平带电位负移,光生载流子在薄膜电极/溶液界面转移速率加快,表面复合速率降低.这些变化和表面积增加是BiVO4电极光电化学性能提高的主要原因.     

ATR-FTIR Investigation of Hydrogen-terminated Si(111) Surface in Various NH4F-Based Solutions

Wet chemical cleaning of silicon is a critical step in the semiconductor manufacturing. Particles, contaminants, metallic impurities, roughness and native oxide on silicon surface after wet chemical cleaning deteriorate the reliability of transistor performance in integrated circuits^[1]. Wet chemical etching of Si(111) and Si(100) in fluoride and alkaline solutions has been extensively studied in the past few years by using scanning tunneling microscopy (STM) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR)^[2-11]. In the present work, we extend our study to Si(111) surface after treating with NH₄F/HCl mixtures. STM, X-ray photo spectroscopy (XPS), and ATR-FTIR are used to determine surface roughness, contamination and bond information on Si(111) surface after wet chemical cleaning with various NH₄F/HCl mixtures. The results are discussed in details by comparison to those treated with RCA and HF solutions, indicating that ultra-clean and flat Si(111) surface is obtained by treatment with NH₄F/HCl mixture.     

Evidence of the synergetic role of charged species and atomic oxygen in the molecular etching of PTFE surfaces for hydrophobic surface synthesis

The transformation of a poly(tetrafluoroethylene) (PTFE) hydrophobic surface into a superhydrophobic one using a low pressure RF plasma is explored using optical emission spectrometry (OES), X-ray photoelectron spectroscopy (XPS), water contact angle (WCA) measurements, mass measurements, and atomic force microscopy (AFM). It is shown that the increase in contact angle is due to an increase of roughness provoked by a chemical etching of the surface. We propose a molecular mechanism for etching that requires the simultaneous presence of atomic oxygen and negatively charged species (electrons) at the PTFE surface.     

Characterization of tungsten surfaces by simultaneous work function and secondary electron emission measurements.

The changes of the work function (Phi) and the secondary electron emission (SEE) of oxygen covered polycrystalline tungsten occurring after ion sputtering and heat treatments have been investigated. The chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS), and the electron emission properties by work function spectroscopy (WFS). We observed in what manner the chemical changes of the surface are reflected in the work function and SEE. The simultaneous change of Phi and SEE in the case of oxygen covered tungsten have been pointed out and a direct relationship between them can be supposed.     

Conversion of isopropyl alcohol to acetone in fullerite cavities

Fullerite with cavities containing dichlorobenzene (DCB) and isopropyl alcohol (IPA) molecules was prepared by the addition of IPA to a solution of fullerene C₆₀ in DCB. On heating in vacuo fullerite evolves IPA, and the temperature increase to 200—350 °C results in the evolution of acetone. No products of DCB conversion were observed. Possible products of the interaction of 60 with two IPA molecules were calculated by the quantum chemical method. New data on the fullerite structure were obtained by transmission electron microscopy X-ray powder diffractometry, mass spectrometry, IR spectroscopy, and other methods. One of the possible mechanisms of the reaction IPA → acetone was considered.     

Influence of sodium sulfate or sodium sulfite on the solubilization of benzylalcohol in cationic micellar solutions

The enthalpy of benzylalcohol (BzOH) solution has been determined as a function of alcohol concentration in aqueous trimethyltetradecylammonium bromide (TTAB) solutions in the presence of sodium sulfite or sodium sulfate up to high salt concentration. The electrolytes studied do not seem to induce TTAB sphere-torod transition at least up to 0.6 mol/kg of salt. Comparison with the enthalpic behavior of BzOH in sodium dodecylsulfate solutions and with that of 1-pentanol in both cationic and anionic micellar solutions suggests that the solubilization of BzOH in TTAB solutions is specifically favored by intramolecular interactions between alcohol molecules within the cationic micelles. The replacement of the bromide counterions by the sulfite or sulfate ions has been studied using potentiometry with an ionselective electrode in the case of trimethylhexadecylammonium bromide (CTAB). No difference could be detected between the effects of either divalent anions on the rate of change of the bromide ion-condensation with the salt/surfactant concentration ratioR. The degree of counter-ion condensation on micellar surface depends not only on theR values, but also on the total surfactant concentration.     

Behaviour of methyl red under fast atom bombardment conditions

The influence of the pH, the nature of the matrix and the presence of a surfactant on the positive- and negative-ion abundances in the molecular mass region in the fast atom bombardment (FAB) mass spectra of methyl red was investigated. A small but significant pH effect was observed which was attributed to the non- or at the most low surface-active character of the intact methyl red molecule. As expected, the more basic the solution, the less protonated molecules with respect to M⁺˙ are observed and in the negative-ion mode less [M + H]^? and more [M – H]^? ions with respect to M^?˙ were found. In contrast to neutral solutions, both acidic and basic solutions give a long-lasting stable response of all methyl red ions. For dyes with a moderately negative redox potential such as methyl red, beam-induced redox reactions seem to play a role in the ionization process, the neutral medium offering the best conditions for reduction processes. The ion intensities in the molecular mass region depend on the nature of the matrix. Protonation of the molecule has been found to be more effective in glycerol than in 3-nitrobenzyl alcohol; the former also appears to offer the best conditions for reduction processes. Anionic and cationic surfactants effectively suppress the contribution of ions from glycerol in both positive- and negative-ion spectra and generally promote the formation of analyte ions at the surface. The most important effect of the surfactant in a neutral medium seems to be the promotion of a regular transport of ions and molecules to the surface, which permits the creation of stable ion currents, instead of an unstable ion beam if the surfactant is absent. Moreover, when the surfactant is present an increase of the sample ion abundances is observed. Redox reactions involving molecules and molecular ions and also molecules and preformed ions in the solution, brought to the surface by micelles, have been proposed to give some contribution for the small but significant enhanced abundance of [M + nH]⁺ (n > 1) ions with respect to [M + H]⁺ ions, in the presence of a surfactant. The results have been rationalized in terms of the surface phenomena while the important role of surfactants for obtaining better FAB mass spectra is emphasized.     

Composite poly(vinyl alcohol)–poly(sulfone) membranes crosslinked by trimesoyl chloride: Characterization and dehydration of ethylene glycol–water mixtures

Composite membranes prepared from poly(vinyl alcohol) and poly(sulfone) were crosslinked with trimesoyl chloride (TMC) solutions. The degree of crosslinking, crystallinity, surface roughness and hydrophobicity of the crosslinked PVA–PSf membranes were determined from attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM) and contact angle measurements, respectively. Results showed a consistent trend of changes in the physicochemical properties: the degree of crosslinking, crystallinity, surface roughness, hydrophobicity and swelling degree all decrease with increasing crosslinking agent (TMC) concentration and reaction time. The crosslinked membrane performance was assessed with pervaporation dehydration of ethylene glycol solutions at a range of concentrations (30–90 wt% EG) in the feed mixtures. The total flux of permeation was found to decrease, while the selectivity to increase, with increasing TMC concentration and reaction time. The decrease in flux was most prominent at low EG concentrations in the feed mixtures. In addition, the temperature effect on the pervaporation dehydration was investigated in relation to solution–diffusion mechanisms.